LP38851 www.ti.com SNVS492C - JUNE 2007 - REVISED APRIL 2013 LP38851 800 mA Fast-Response High-Accuracy Adjustable LDO Linear Regulator with Enable and Soft-Start Check for Samples: LP38851 FEATURES DESCRIPTION * * The LP38851-ADJ is a high current, fast response regulator which can maintain output voltage regulation with extremely low input to output voltage drop. Fabricated on a CMOS process, the device operates from two input voltages: VBIAS provides voltage to drive the gate of the N-MOS power transistor, while VIN is the input voltage which supplies power to the load. The use of an external bias rail allows the part to operate from ultra low VIN voltages. Unlike bipolar regulators, the CMOS architecture consumes extremely low quiescent current at any output load current. The use of an NMOS power transistor results in wide bandwidth, yet minimum external capacitance is required to maintain loop stability. 1 2 * * * * * * Adjustable VOUT Range of 0.80V to 1.8V Wide VBIAS Supply Operating Range of 3.0V to 5.5V Stable with 10F Ceramic Capacitors Dropout Voltage of 115 mV (Typical) at 800 mA Load Current Precision VADJ across All Line and Load Conditions: - 1.5% VADJ for TJ = 25C - 2.0% VADJ for 0C TJ +125C - 3.0% VADJ for -40C TJ +125C Over-Temperature and Over-Current Protection Available in 8-Lead SO PowerPad, 7-Lead SFM and 7-Lead PFM Packages -40C to +125C Operating Junction Temperature Range APPLICATIONS * * * * ASIC Power Supplies in: - Desktops, Notebooks, and Graphics Cards, Servers - Gaming Set Top Boxes, Printers and Copiers Server Core and I/O Supplies DSP and FPGA Power Supplies SMPS Post-Regulator The fast transient response of this device makes it suitable for use in powering DSP, Microcontroller Core voltages and Switch Mode Power Supply post regulators. The part is available in PSOP 8-pin, SFM 7-pin, and TO-263 7-pin packages. * Dropout Voltage: 115 mV (typical) at 800 mA load current * Low Ground Pin Current: 10 mA (typical) at 800 mA load current * Soft-Start: Programmable Soft-Start time * Precision ADJ Voltage: 1.5% for TJ = 25C, and 2.0% for 0C TJ +125C, across all line and load conditions 1 2 Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet. All trademarks are the property of their respective owners. PRODUCTION DATA information is current as of publication date. Products conform to specifications per the terms of the Texas Instruments standard warranty. Production processing does not necessarily include testing of all parameters. Copyright (c) 2007-2013, Texas Instruments Incorporated LP38851 SNVS492C - JUNE 2007 - REVISED APRIL 2013 www.ti.com TYPICAL APPLICATION CIRCUIT LP38851-ADJ VIN IN VBIAS VOUT OUT CIN 10 PF Ceramic CFF R1 BIAS CBIAS 1 PF VEN SS COUT 10 PF Ceramic ADJ EN R2 GND CSS GND GND Connection Diagram 1 2 3 4 5 6 7 TAB IS GND LP38851S-ADJ SS EN IN GND ADJ OUT BIAS 7 IN BIAS 3 6 EN GND 4 5 SS Figure 3. 8-Lead SO PowerPad - Top View See DDA Package TAB IS GND LP38851T-ADJ 1 2 3 4 5 6 7 8 N/C DAP Connect to GND Figure 1. 7-Lead PFM - Top View See KTW0007B Package SS EN IN GND ADJ OUT BIAS ADJ 1 OUT 2 Figure 2. 7-Lead SFM - Top View See NDZ0007B Package PIN DESCRIPTIONS 2 SFM Pin # PFM Pin # SO PowerPad Pin # Pin Symbol 1 1 5 SS Soft-Start capacitor connection. Used to control the rise time of VOUT at turn-on. 2 2 6 EN Device Enable, High = On, Low = Off. 3 3 7 IN The unregulated voltage input 4 4 4 GND Ground 5 5 1 ADJ The feedback connection to set the output voltage 6 6 2 OUT The regulated output voltage 7 7 3 BIAS The supply for the internal control and reference circuitry. - - 8 N/C No internal connection TAB TAB - TAB The SFM and PFM TAB is a thermal and electrical connection that is physically attached to the backside of the die, and used as a thermal heat-sink connection. See APPLICATION INFORMATION for details. Pin Description Submit Documentation Feedback Copyright (c) 2007-2013, Texas Instruments Incorporated Product Folder Links: LP38851 LP38851 www.ti.com SNVS492C - JUNE 2007 - REVISED APRIL 2013 PIN DESCRIPTIONS (continued) SFM Pin # PFM Pin # SO PowerPad Pin # Pin Symbol - - DAP DAP Pin Description The SO PowerPad DAP is a thermal connection only that is physically attached to the backside of the die, and used as a thermal heat-sink connection. See APPLICATION INFORMATION for details. These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam during storage or handling to prevent electrostatic damage to the MOS gates. ABSOLUTE MAXIMUM RATINGS (1) -65C to +150C Storage Temperature Range Lead Temperature Soldering, 5 seconds ESD Rating Power Dissipation Human Body Model 260C (2) (3) 2 kV Internally Limited VIN Supply Voltage (Survival) -0.3V to +6.0V VBIAS Supply Voltage (Survival) -0.3V to +6.0V VSS SoftStart Voltage (Survival) -0.3V to +6.0V VOUT Voltage (Survival) -0.3V to +6.0V IOUT Current (Survival) Internally Limited Junction Temperature -40C to +150C (1) (2) (3) Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is intended to be functional, but does not ensure specific performance limits. For specifications and conditions, see the Electrical Characteristics. The human body model is a 100 pF capacitor discharged through a 1.5k resistor into each pin. Test method is per JESD22-A114. Device power dissipation must be de-rated based on device power dissipation (PD), ambient temperature (TA), and package junction to ambient thermal resistance (JA). Additional heat-sinking may be required to ensure that the device junction temperature (TJ) does not exceed the maximum operating rating. See APPLICATION INFORMATION for details. OPERATING RATINGS (1) VIN Supply Voltage (VOUT + VDO) to VBIAS 0.8V VOUT 1.2V VBIAS Supply Voltage 1.2V < VOUT 1.8V VEN Voltage 0 mA to 800 mA Junction Temperature Range (2) 4.5V to 5.5V 0.0V to VBIAS IOUT (1) 3.0V to 5.5V (2) -40C to +125C Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is intended to be functional, but does not ensure specific performance limits. For specifications and conditions, see the Electrical Characteristics. Device power dissipation must be de-rated based on device power dissipation (PD), ambient temperature (TA), and package junction to ambient thermal resistance (JA). Additional heat-sinking may be required to ensure that the device junction temperature (TJ) does not exceed the maximum operating rating. See APPLICATION INFORMATION for details. Submit Documentation Feedback Copyright (c) 2007-2013, Texas Instruments Incorporated Product Folder Links: LP38851 3 LP38851 SNVS492C - JUNE 2007 - REVISED APRIL 2013 www.ti.com ELECTRICAL CHARACTERISTICS Unless otherwise specified: VOUT = 0.80V, VIN = VOUT(NOM) + 1V, VBIAS = 3.0V, VEN = VBIAS, IOUT = 10 mA, CIN = COUT = 10 F, CBIAS = 1 F, CSS = open. Limits in standard type are for TJ = 25C only; limits in boldface type apply over the junction temperature (TJ) range of -40C to +125C. Minimum and Maximum limits are specified through test, design, or statistical correlation. Typical values represent the most likely parametric norm at TJ = 25C, and are provided for reference purposes only. Symbol VADJ VOUT VOUT/VIN VOUT/VBIAS VOUT/IOUT VDO IGND(IN) Parameter Conditions VADJ Accuracy VOUT Range VOUT(NOM)+1V VIN VBIAS 4.5V 3.0V VBIAS 5.5V, 10 mA IOUT 800 mA (1) VOUT(NOM)+1V VIN VBIAS 4.5V 3.0V VBIAS 5.5V, 10 mA IOUT 800 mA, 0C TJ +125C (1) Min Typ Max 492.5 485.0 500. 507.5 515.0 mV 490.0 510.0 0.80 1.20 4.5V VBIAS 5.5V 0.80 1.80 V Line Regulation, VIN (2) VOUT(NOM)+1V VIN VBIAS - 0.04 - %/V Line Regulation, VBIAS (2) 3.0V VBIAS 5.5V - 0.10 - %/V 10 mA IOUT 800 mA - 0.2 - %/A mV Output Voltage Load Regulation Dropout Voltage (3) (4) Quiescent Current Drawn from VIN Supply IOUT = 800 mA - 115 150 200 VOUT = 0.80V VBIAS = 3.0V 10 mA IOUT 800 mA - 7.0 8.5 9.0 mA 1 100 300 A Quiescent Current Drawn from VBIAS Supply 3.0 3.8 4.5 mA 100 170 200 A 2.20 2.00 2.45 2.70 2.90 V 60 50 150 300 350 mV - 2.3 - A 11.0 14.0 17.0 k - 700 - s - 10 mA IOUT 800 mA - VEN 0.5V UVLO Under-Voltage Lock-Out Threshold VBIAS rising until device is functional UVLO(HYS) Under-Voltage Lock-Out Hysteresis VBIAS falling from UVLO threshold until device is non-functional Output Short-Circuit Current VIN = VOUT(NOM) + 1V, VBIAS = 3.0V, VOUT = 0.0V ISC 500. 3.0V VBIAS 5.5V VEN 0.5V IGND(BIAS) Units Soft-Start rSS Soft-Start internal resistance tSS Soft-Start time tSS = CSS x rSS x 5 CSS = 10 nF Enable VEN = VBIAS IEN ENABLE pin Current 0.01 - VEN = 0.0V, VBIAS = 5.5V -24 -21 -35 -43 -50 1.00 0.90 1.25 1.50 1.55 V 50 30 100 150 200 mV VEN(ON) Enable Voltage Threshold VEN rising until Output = ON VEN(HYS) Enable Voltage Hysteresis VEN falling from VEN(ON) until Output = OFF tOFF Turn-OFF Delay Time RLOAD x COUT << tOFF - 20 - tON Turn-ON Delay Time RLOAD x COUT << tON - 15 - A s AC Parameters (1) (2) (3) (4) 4 VIN cannot exceed either VBIAS or 4.5V, whichever value is lower. Output voltage line regulation is defined as the change in output voltage from nominal value resulting from a change in input voltage. Output voltage load regulation is defined as the change in output voltage from nominal value as the load current increases from no load to full load. Dropout voltage is defined as the input to output voltage differential (VIN - VOUT) where the input voltage is low enough to cause the output voltage to drop 2% from the nominal value. Submit Documentation Feedback Copyright (c) 2007-2013, Texas Instruments Incorporated Product Folder Links: LP38851 LP38851 www.ti.com SNVS492C - JUNE 2007 - REVISED APRIL 2013 ELECTRICAL CHARACTERISTICS (continued) Unless otherwise specified: VOUT = 0.80V, VIN = VOUT(NOM) + 1V, VBIAS = 3.0V, VEN = VBIAS, IOUT = 10 mA, CIN = COUT = 10 F, CBIAS = 1 F, CSS = open. Limits in standard type are for TJ = 25C only; limits in boldface type apply over the junction temperature (TJ) range of -40C to +125C. Minimum and Maximum limits are specified through test, design, or statistical correlation. Typical values represent the most likely parametric norm at TJ = 25C, and are provided for reference purposes only. Symbol PSRR (VIN) PSRR (VBIAS) Parameter Min Typ Max VIN = VOUT(NOM) + 1V, f = 120 Hz - 72 - VIN = VOUT(NOM) + 1V, f = 1 kHz - 61 - VBIAS = VOUT(NOM) + 3V, f = 120 Hz - 54 - VBIAS = VOUT(NOM) + 3V, f = 1 kHz - 53 - f = 120 Hz - 1 - BW = 10 Hz - 100 kHz - 150 - BW = 300 Hz - 300 kHz - 90 - Thermal Shutdown Junction Temperature - 160 - Thermal Shutdown Hysteresis - 10 - SFM - 60 - PFM - 60 - SO PowerPad - 168 - SFM - 3 - PFM - 3 - SO PowerPad - 11 - Ripple Rejection for VIN Input Voltage Ripple Rejection for VBIAS Voltage Output Noise Density en Output Noise Voltage Conditions Units dB V/Hz VRMS Thermal Parameters TSD TSD(HYS) J-A J-C (5) (6) Thermal Resistance, Junction to Ambient (5) Thermal Resistance, Junction to Case (5) (6) C C/W Device power dissipation must be de-rated based on device power dissipation (PD), ambient temperature (TA), and package junction to ambient thermal resistance (JA). Additional heat-sinking may be required to ensure that the device junction temperature (TJ) does not exceed the maximum operating rating. See APPLICATION INFORMATION for details. For SFM and PFM: J-C refers to the BOTTOM surface of the package, under the epoxy body, as the 'CASE'. For SO PowerPad: J-C refers to the DAP (aka: Exposed Pad) on BOTTOM surface of the package as the 'CASE'. Submit Documentation Feedback Copyright (c) 2007-2013, Texas Instruments Incorporated Product Folder Links: LP38851 5 LP38851 SNVS492C - JUNE 2007 - REVISED APRIL 2013 www.ti.com TYPICAL PERFORMANCE CHARACTERISTICS Refer to the TYPICAL APPLICATION CIRCUIT. Unless otherwise specified: TJ = 25C, R1 = 1.40 k, R2 = 1.00 k, CFF= 180 pF, VIN = VOUT(NOM) + 1V, VBIAS = 3.0V, IOUT = 10 mA, CIN = 10 F Ceramic, COUT = 10 F Ceramic, CBIAS = 1 F Ceramic, , CSS = Open. 6 VBIAS Ground Pin Current (IGND(BIAS)) vs VBIAS VBIAS Ground Pin Current (IGND(BIAS)) vs Temperature Figure 4. Figure . VIN Ground Pin Current vs Temperature Load Regulation vs Temperature Figure 5. Figure 6. Dropout Voltage (VDO) vs Temperature Output Current Limit (ISC) vs Temperature Figure 7. Figure 8. Submit Documentation Feedback Copyright (c) 2007-2013, Texas Instruments Incorporated Product Folder Links: LP38851 LP38851 www.ti.com SNVS492C - JUNE 2007 - REVISED APRIL 2013 TYPICAL PERFORMANCE CHARACTERISTICS (continued) Refer to the TYPICAL APPLICATION CIRCUIT. Unless otherwise specified: TJ = 25C, R1 = 1.40 k, R2 = 1.00 k, CFF= 180 pF, VIN = VOUT(NOM) + 1V, VBIAS = 3.0V, IOUT = 10 mA, CIN = 10 F Ceramic, COUT = 10 F Ceramic, CBIAS = 1 F Ceramic, , CSS = Open. VOUT vs Temperature VOUT vs VIN Figure 9. Figure 10. UVLO Thresholds vs Temperature Soft-Start rSS Variation vs Temperature Figure 11. Figure 12. VOUT vs CSS, 10 nF to 47 nF Enable Thresholds (VEN) vs Temperature Figure 13. Figure 14. Submit Documentation Feedback Copyright (c) 2007-2013, Texas Instruments Incorporated Product Folder Links: LP38851 7 LP38851 SNVS492C - JUNE 2007 - REVISED APRIL 2013 www.ti.com TYPICAL PERFORMANCE CHARACTERISTICS (continued) Refer to the TYPICAL APPLICATION CIRCUIT. Unless otherwise specified: TJ = 25C, R1 = 1.40 k, R2 = 1.00 k, CFF= 180 pF, VIN = VOUT(NOM) + 1V, VBIAS = 3.0V, IOUT = 10 mA, CIN = 10 F Ceramic, COUT = 10 F Ceramic, CBIAS = 1 F Ceramic, , CSS = Open. 8 Enable Pull-Down Current (IEN) vs Temperature Enable Pull-Up Resistor (rEN) vs Temperature Figure 15. Figure 16. VIN Line Transient Response VIN Line Transient Response Figure 17. Figure 18. VBIAS Line Transient Response VBIAS Line Transient Response Figure 19. Figure 20. Submit Documentation Feedback Copyright (c) 2007-2013, Texas Instruments Incorporated Product Folder Links: LP38851 LP38851 www.ti.com SNVS492C - JUNE 2007 - REVISED APRIL 2013 TYPICAL PERFORMANCE CHARACTERISTICS (continued) Refer to the TYPICAL APPLICATION CIRCUIT. Unless otherwise specified: TJ = 25C, R1 = 1.40 k, R2 = 1.00 k, CFF= 180 pF, VIN = VOUT(NOM) + 1V, VBIAS = 3.0V, IOUT = 10 mA, CIN = 10 F Ceramic, COUT = 10 F Ceramic, CBIAS = 1 F Ceramic, , CSS = Open. Load Transient Response, COUT = 10 F Ceramic Load Transient Response, COUT = 10 F Ceramic Figure 21. Figure 22. Load Transient Response, COUT = 47 F Ceramic Load Transient Response, COUT = 47 F Ceramic Figure 23. Figure 24. Load Transient Response, COUT = 68 F Tantalum Load Transient Response, COUT = 68 F Tantalum Figure 25. Figure 26. Submit Documentation Feedback Copyright (c) 2007-2013, Texas Instruments Incorporated Product Folder Links: LP38851 9 LP38851 SNVS492C - JUNE 2007 - REVISED APRIL 2013 www.ti.com TYPICAL PERFORMANCE CHARACTERISTICS (continued) Refer to the TYPICAL APPLICATION CIRCUIT. Unless otherwise specified: TJ = 25C, R1 = 1.40 k, R2 = 1.00 k, CFF= 180 pF, VIN = VOUT(NOM) + 1V, VBIAS = 3.0V, IOUT = 10 mA, CIN = 10 F Ceramic, COUT = 10 F Ceramic, CBIAS = 1 F Ceramic, , CSS = Open. VBIAS PSRR VIN PSRR Figure 27. Figure 28. Output Noise Figure 29. 10 Submit Documentation Feedback Copyright (c) 2007-2013, Texas Instruments Incorporated Product Folder Links: LP38851 LP38851 www.ti.com SNVS492C - JUNE 2007 - REVISED APRIL 2013 BLOCK DIAGRAM OUT IN LP38851-ADJ BIAS Under-Voltage Lock-Out Thermal Shut Down rEN ADJ EN Enable 1.2V rSS SS VREF ILIMIT GND 0.5V Submit Documentation Feedback Copyright (c) 2007-2013, Texas Instruments Incorporated Product Folder Links: LP38851 11 LP38851 SNVS492C - JUNE 2007 - REVISED APRIL 2013 www.ti.com APPLICATION INFORMATION EXTERNAL CAPACITORS To assure regulator stability, input and output capacitors are required as shown in TYPICAL APPLICATION CIRCUIT. Output Capacitor A minimum output capacitance of 10 F, ceramic, is required for stability. The amount of output capacitance can be increased without limit. The output capacitor must be located less than 1 cm from the output pin of the IC and returned to the device ground pin with a clean analog ground. Only high quality ceramic types such as X5R or X7R should be used, as the Z5U and Y5F types do not provide sufficient capacitance over temperature. Tantalum capacitors will also provide stable operation across the entire operating temperature range. However, the effects of ESR may provide variations in the output voltage during fast load transients. Using the minimum recommended 10 F ceramic capacitor at the output will allow unlimited capacitance, Tantalum and/or Aluminum, to be added in parallel. Input Capacitor The input capacitor must be at least 10 F, but can be increased without limit. It's purpose is to provide a low source impedance for the regulator input. A ceramic capacitor, X5R or X7R, is recommended. Tantalum capacitors may also be used at the input pin. There is no specific ESR limitation on the input capacitor (the lower, the better). Aluminum electrolytic capacitors can be used, but are not recommended as their ESR increases very quickly at cold temperatures. They are not recommended for any application where the ambient temperature falls below 0C. Bias Capacitor The capacitor on the bias pin must be at least 1 F, and can be any good quality capacitor (ceramic is recommended). Feed Forward Capacitor, CFF (Refer to TYPICAL APPLICATION CIRCUIT) When using a ceramic capacitor for COUT, the typical ESR value will be too small to provide any meaningful positive phase compensation, FZ, to offset the internal negative phase shifts in the gain loop. FZ = 1 / (2 x x COUT x ESR) (1) A capacitor placed across the gain resistor R1 will provide additional phase margin to improve load transient response of the device. This capacitor, CFF, in parallel with R1, will form a zero in the loop response given by the formula: FZ = 1 / (2 x x CFF x R1) (2) For optimum load transient response select CFF so the zero frequency, FZ, falls between 500 kHz and 750 kHz. CFF = 1 / (2 x x R1 x FZ) (3) The phase lead provided by CFF diminishes as the DC gain approaches unity, or VOUT approaches VADJ. This is because CFF also forms a pole with a frequency of: FP = 1 / (2 x x CFF x (R1 || R2) ) (4) It's important to note that at higher output voltages, where R1 is much larger than R2, the pole and zero are far apart in frequency. At lower output voltages the frequency of the pole and the zero mover closer together. The phase lead provided from CFF diminishes quickly as the output voltage is reduced, and has no effect when VOUT = VADJ. For this reason, relying on this compensation technique alone is adequate only for higher output voltages. For the LP38851, the practical minimum VOUT is 0.8V when a ceramic capacitor is used for COUT. 12 Submit Documentation Feedback Copyright (c) 2007-2013, Texas Instruments Incorporated Product Folder Links: LP38851 LP38851 www.ti.com SNVS492C - JUNE 2007 - REVISED APRIL 2013 Figure 30. FZERO and FPOLE vs Gain SETTING THE OUTPUT VOLTAGE (Refer to TYPICAL APPLICATION CIRCUIT) The output voltage is set using the external resistive divider R1 and R2. The output voltage is given by the formula: R1 ** VOUT = VADJ x 1 + (c) (c) R2 (5) The resistors used for R1 and R2 should be high quality, tight tolerance, and with matching temperature coefficients. It is important to remember that, although the value of VADJ is specified, the use of low quality resistors for R1 and R2 can easily produce a VOUT value that is unacceptable. It is recommended that the values selected for R1 and R2 are such that the parallel value is less than 10 k. This is to prevent internal parasitic capacitances on the ADJ pin from interfering with the FZ pole set by R1 and CFF. ( (R1 x R2) / (R1 + R2) ) 10 k (6) Table 1 lists some suggested, best fit, standard 1% resistor values for R1 and R2, and a standard 10% capacitor values for CFF, for a range of VOUT values. Other values of R1, R2, and CFF are available that will give similar results. Table 1. VOUT R1 R2 CFF FZ 0.8V 1.07 k 1.78 k 220 pF 676 kHz 0.9V 1.50 k 1.87 k 180 pF 589 kHz 1.00V 1.00 k 1.00 k 270 pF 589 kHz 1.1V 1.65 k 1.37 k 150 pF 643 kHz 1.2V 1.40 k 1.00 k 180 pF 631 kHz 1.3V 1.15 k 715 220 pF 629 kHz 1.4V 1.07 k 590 220 pF 676 kHz 1.5V 2.00 k 1.00 k 120pF 663 kHz 1.6V 1.65 k 750 150 pF 643 kHz 1.7V 2.55 k 1.07 k 100 pF 624 kHz 1.8V 2.94 k 1.13 k 82 pF 660 kHz Submit Documentation Feedback Copyright (c) 2007-2013, Texas Instruments Incorporated Product Folder Links: LP38851 13 LP38851 SNVS492C - JUNE 2007 - REVISED APRIL 2013 www.ti.com Please refer to Application Note AN-1378 (SNVA112) for additional information on how resistor tolerances affect the calculated VOUT value. INPUT VOLTAGE The input voltage (VIN) is the high current external voltage rail that will be regulated down to a lower voltage, which is applied to the load. The input voltage must be at least VOUT + VDO, and no higher than whatever value is used for VBIAS. For applications where VBIAS is higher than 4.5V, VIN must be no greater than 4.5V, otherwise output voltage accuracy may be affected. BIAS VOLTAGE The bias voltage (VBIAS) is a low current external voltage rail required to bias the control circuitry and provide gate drive for the N-FET pass transistor. When VOUT is set to 1.20V, or less, VBIAS may be anywhere in the operating range of 3.0V to 5.5V. If VOUT is set higher than 1.20V , VBIAS must be between 4.5V and 5.5V to ensure proper operation of the device. UNDER VOLTAGE LOCKOUT The bias voltage is monitored by a circuit which prevents the device from functioning when the bias voltage is below the Under-Voltage Lock-Out (UVLO) threshold of approximately 2.45V. As the bias voltage rises above the UVLO threshold the device control circuitry becomes active. There is approximately 150 mV of hysteresis built into the UVLO threshold to provide noise immunity. When the bias voltage is between the UVLO threshold and the Minimum Operating Rating value of 3.0V the device will be functional, but the operating parameters will not be within the specified limits. SUPPLY SEQUENCING There is no requirement for the order that VIN or VBIAS are applied or removed. One practical limitation is that the Soft-Start circuit starts charging CSS when both VBIAS rises above the UVLO threshold and the Enable pin is above the VEN(ON) threshold. If the application of VIN is delayed beyond this point the benefits of Soft-Start will be compromised. In any case, the output voltage cannot be specified until both VIN and VBIAS are within the range of specified operating values. If used in a dual-supply system where the regulator output load is returned to a negative supply, the output pin must be diode clamped to ground. A Schottky diode is recommended for this diode clamp. REVERSE VOLTAGE A reverse voltage condition will exist when the voltage at the output pin is higher than the voltage at the input pin. Typically this will happen when VIN is abruptly taken low and COUT continues to hold a sufficient charge such that the input to output voltage becomes reversed. The NMOS pass element, by design, contains no body diode. This means that, as long as the gate of the pass element is not driven, there will not be any reverse current flow through the pass element during a reverse voltage event. The gate of the pass element is not driven when VBIAS is below the UVLO threshold, or when the Enable pin is held low. When VBIAS is above the UVLO threshold, and the Enable pin is above the VEN(ON) threshold, the control circuitry is active and will attempt to regulate the output voltage. Since the input voltage is less than the output voltage the control circuit will drive the gate of the pass element to the full VBIAS potential when the output voltage begins to fall. In this condition, reverse current will flow from the output pin to the input pin , limited only by the RDS(ON) of the pass element and the output to input voltage differential. Discharging an output capacitor up 1000 F in this manner will not damage the device as the current will rapidly decay. However, continuous reverse current should be avoided. 14 Submit Documentation Feedback Copyright (c) 2007-2013, Texas Instruments Incorporated Product Folder Links: LP38851 LP38851 www.ti.com SNVS492C - JUNE 2007 - REVISED APRIL 2013 SOFT-START The LP38851 incorporates a Soft-Start function that reduces the start-up current surge into the output capacitor (COUT) by allowing VOUT to rise slowly to the final value. This is accomplished by controlling VREF at the SS pin. The soft-start timing capacitor (CSS) is internally held to ground until both VBIAS rises above the Under-Voltage Lock-Out threshold (ULVO) and the Enable pin is higher than the VEN(ON) threshold. VREF will rise at an RC rate defined by the internal resistance of the SS pin (rSS), and the external capacitor connected to the SS pin. This allows the output voltage to rise in a controlled manner until steady-state regulation is achieved. Typically, five time constants are recommended to assure that the output voltage is sufficiently close to the final steady-state value. During the soft-start time the output current can rise to the built-in current limit. Soft-Start Time = CSS x rSS x 5 (7) Since the VOUT rise will be exponential, not linear, the in-rush current will peak during the first time constant (), and VOUT will require four additional time constants (4) to reach the final value (5) . After achieving normal operation, should either VBIAS fall below the ULVO threshold, or the Enable pin fall below the VEN(OFF) threshold, the device output will be disabled and the Soft-Start capacitor (CSS) discharge circuit will become active. The CSS discharge circuit will remain active until VBIAS falls to 500 mV (typical). When VBIAS falls below 500 mV (typical), the CSS discharge circuit will cease to function due to a lack of sufficient biasing to the control circuitry. Since VREF appears on the SS pin, any leakage through CSS will cause VREF to fall, and thus affect VOUT. A leakage of 50 nA (about 10 M) through CSS will cause VOUT to be approximately 0.1% lower than nominal, while a leakage of 500 nA (about 1 M) will cause VOUT to be approximately 1% lower than nominal. Typical ceramic capacitors will have a factor of 10X difference in leakage between 25C and 85C, so the maximum ambient temperature must be included in the capacitor selection process. Typical CSS values will be in the range of 1 nF to 100 nF, providing typical Soft-Start times in the range of 70 s to 7 ms (5). Values less than 1 nF can be used, but the Soft-Start effect will be minimal. Values larger than 100 nF will provide soft-start, but may not be fully discharged if VBIAS falls from the UVLVO threshold to less than 500 mV in less than 100 s. Figure 31 shows the relationship between the COUT value and a typical CSS value. Figure 31. Typical CSS vs COUT Values The CSS capacitor must be connected to a clean ground path back to the device ground pin. No components, other than CSS, should be connected to the SS pin, as there could be adverse effects to VOUT. If the Soft-Start function is not needed the SS pin should be left open, although some minimal capacitance value is always recommended. Submit Documentation Feedback Copyright (c) 2007-2013, Texas Instruments Incorporated Product Folder Links: LP38851 15 LP38851 SNVS492C - JUNE 2007 - REVISED APRIL 2013 www.ti.com ENABLE OPERATION The Enable pin (EN) provides a mechanism to enable, or disable, the regulator output stage. The Enable pin has an internal pull-up, through a typical 160 k resistor, to VBIAS. If the Enable pin is actively driven, pulling the Enable pin above the VEN threshold of 1.25V (typical) will turn the regulator output on, while pulling the Enable pin below the VEN threshold will turn the regulator output off. There is approximately 100 mV of hysteresis built into the Enable threshold provide noise immunity. If the Enable function is not needed this pin should be left open, or connected directly to VBIAS. If the Enable pin is left open, stray capacitance on this pin must be minimized, otherwise the output turn-on will be delayed while the stray capacitance is charged through the internal resistance (rEN). POWER DISSIPATION AND HEAT-SINKING Additional copper area for heat-sinking may be required depending on the maximum device dissipation (PD) and the maximum anticipated ambient temperature (TA) for the device. Under all possible conditions, the junction temperature must be within the range specified under operating conditions. The total power dissipation of the device is the sum of three different points of dissipation in the device. The first part is the power that is dissipated in the NMOS pass element, and can be determined with the formula: PD(PASS) = (VIN - VOUT) x IOUT (8) The second part is the power that is dissipated in the bias and control circuitry, and can be determined with the formula: PD(BIAS) = VBIAS x IGND(BIAS) where * IGND(BIAS) is the portion of the operating ground current of the device that is related to VBIAS (9) The third part is the power that is dissipated in portions of the output stage circuitry, and can be determined with the formula: PD(IN) = VIN x IGND(IN) where * IGND(IN) is the portion of the operating ground current of the device that is related to VIN (10) The total power dissipation is then: PD = PD(PASS) + PD(BIAS) + PD(IN) (11) The maximum allowable junction temperature rise (TJ) depends on the maximum anticipated ambient temperature (TA) for the application, and the maximum allowable operating junction temperature (TJ(MAX)) . 'J = TJ(MAX) - TA(MAX) (12) The maximum allowable value for junction to ambient Thermal Resistance, JA, can be calculated using the formula: TJA d 'TJ PD (13) Heat-Sinking The SFM Package The SFM package has a JA rating of 60C/W and a JC rating of 3C/W. These ratings are for the package only, no additional heat-sinking, and with no airflow. If the needed JA, as calculated above, is greater than or equal to 60C/W then no additional heat-sinking is required since the package can safely dissipate the heat and not exceed the operating TJ(MAX). If the needed JA is less than 60C/W then additional heat-sinking is needed. The thermal resistance of a SFM package can be reduced by attaching it to a heat sink or a copper plane on a PC board. If a copper plane is to be used, the values of JA will be same as shown in next section for PFM package. The heat-sink to be used in the application should have a heat-sink to ambient thermal resistance, HA: HA JA - (CH + JC) 16 Submit Documentation Feedback Copyright (c) 2007-2013, Texas Instruments Incorporated Product Folder Links: LP38851 LP38851 www.ti.com SNVS492C - JUNE 2007 - REVISED APRIL 2013 T H d T J - (T C + T J ) A A H C where * * JA is the required total thermal resistance from the junction to the ambient air, CH is the thermal resistance from the case to the surface of the heart-sink JC is the thermal resistance from the junction to the surface of the case (14) For this equation, JC is about 3C/W for a SFM package. The value for CH depends on method of attachment, insulator, etc. CH varies between 1.5C/W to 2.5C/W. Consult the heat-sink manufacturer datasheet for details and recommendations. Heat-Sinking The PFM Package The PFM package has a JA rating of 60C/W, and a JC rating of 3C/W. These ratings are for the package only, no additional heat-sinking, and with no airflow. The PFM package uses the copper plane on the PCB as a heat-sink. The tab of this package is soldered to the copper plane for heat sinking. Figure 32 shows a curve for the JA of PFM package for different copper area sizes, using a typical PCB with 1 ounce copper and no solder mask over the copper area for heat-sinking. Figure 32. JA vs Copper (1 Ounce) Area for the PFM package Figure 32 shows that increasing the copper area beyond 1 square inch produces very little improvement. The minimum value for JA for the PFM package mounted to a PCB is 32C/W. Figure 33. Maximum Power Dissipation vs Ambient Temperature for the PFM Package Figure 33 shows the maximum allowable power dissipation for PFM packages for different ambient temperatures, assuming JA is 35C/W and the maximum junction temperature is 125C. Submit Documentation Feedback Copyright (c) 2007-2013, Texas Instruments Incorporated Product Folder Links: LP38851 17 LP38851 SNVS492C - JUNE 2007 - REVISED APRIL 2013 www.ti.com Heat-Sinking The SO PowerPad Package The LP38851MR package has a JA rating of 168C/W, and a JC rating of 11C/W. The JA rating of 168C/W includes the device DAP soldered to an area of 0.008 square inches (0.09 in x 0.09 in) of 1 ounce copper, with no airflow. Figure 34. JA vs Copper (1 Ounce) Area for the SO PowerPad Package Increasing the copper area soldered to the DAP to 1 square inch of 1 ounce copper, using a dog-bone type layout, will improve the JA rating to 98C/W. Figure 34 shows that increasing the copper area beyond 1 square inch produces very little improvement. Figure 35. Maximum Power Dissipation vs Ambient Temperature for the SO PowerPad Package Figure 35 shows the maximum allowable power dissipation for the SO PowerPad package for a range of ambient temperatures, assuming JA is 98C/W and the maximum junction temperature is 125C. 18 Submit Documentation Feedback Copyright (c) 2007-2013, Texas Instruments Incorporated Product Folder Links: LP38851 LP38851 www.ti.com SNVS492C - JUNE 2007 - REVISED APRIL 2013 REVISION HISTORY Changes from Revision B (April 2013) to Revision C * Page Changed layout of National Data Sheet to TI format .......................................................................................................... 18 Submit Documentation Feedback Copyright (c) 2007-2013, Texas Instruments Incorporated Product Folder Links: LP38851 19 PACKAGE OPTION ADDENDUM www.ti.com 10-Dec-2020 PACKAGING INFORMATION Orderable Device Status (1) Package Type Package Pins Package Drawing Qty Eco Plan (2) Lead finish/ Ball material MSL Peak Temp Op Temp (C) Device Marking (3) (4/5) (6) LP38851MR-ADJ/NOPB ACTIVE SO PowerPAD DDA 8 95 RoHS & Green SN Level-3-260C-168 HR -40 to 125 L38851 MRADJ LP38851MRX-ADJ/NOPB ACTIVE SO PowerPAD DDA 8 2500 RoHS & Green SN Level-3-260C-168 HR -40 to 125 L38851 MRADJ LP38851S-ADJ/NOPB ACTIVE DDPAK/ TO-263 KTW 7 45 RoHS-Exempt & Green SN Level-3-245C-168 HR -40 to 125 LP38851S -ADJ LP38851SX-ADJ/NOPB ACTIVE DDPAK/ TO-263 KTW 7 500 RoHS-Exempt & Green SN Level-3-245C-168 HR -40 to 125 LP38851S -ADJ LP38851T-ADJ/NOPB ACTIVE TO-220 NDZ 7 45 RoHS & Green SN Level-1-NA-UNLIM -40 to 125 LP38851T -ADJ (1) The marketing status values are defined as follows: ACTIVE: Product device recommended for new designs. LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect. NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design. PREVIEW: Device has been announced but is not in production. Samples may or may not be available. OBSOLETE: TI has discontinued the production of the device. (2) RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may reference these types of products as "Pb-Free". RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption. Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of <=1000ppm threshold. Antimony trioxide based flame retardants must also meet the <=1000ppm threshold requirement. (3) MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature. (4) There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device. (5) Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation of the previous line and the two combined represent the entire Device Marking for that device. (6) Lead finish/Ball material - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead finish/Ball material values may wrap to two lines if the finish value exceeds the maximum column width. Addendum-Page 1 Samples PACKAGE OPTION ADDENDUM www.ti.com 10-Dec-2020 Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals. TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release. In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis. Addendum-Page 2 PACKAGE MATERIALS INFORMATION www.ti.com 23-Sep-2013 TAPE AND REEL INFORMATION *All dimensions are nominal Device Package Package Pins Type Drawing SPQ Reel Reel A0 Diameter Width (mm) (mm) W1 (mm) B0 (mm) K0 (mm) P1 (mm) W Pin1 (mm) Quadrant LP38851MRX-ADJ/NOPB SO Power PAD DDA 8 2500 330.0 12.4 6.5 5.4 2.0 8.0 12.0 Q1 LP38851SX-ADJ/NOPB DDPAK/ TO-263 KTW 7 500 330.0 24.4 10.75 14.85 5.0 16.0 24.0 Q2 Pack Materials-Page 1 PACKAGE MATERIALS INFORMATION www.ti.com 23-Sep-2013 *All dimensions are nominal Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm) LP38851MRX-ADJ/NOPB SO PowerPAD DDA 8 2500 367.0 367.0 35.0 LP38851SX-ADJ/NOPB DDPAK/TO-263 KTW 7 500 367.0 367.0 45.0 Pack Materials-Page 2 MECHANICAL DATA KTW0007B TS7B (Rev E) BOTTOM SIDE OF PACKAGE www.ti.com PACKAGE OUTLINE DDA0008A PowerPAD TM SOIC - 1.7 mm max height SCALE 2.400 PLASTIC SMALL OUTLINE C 6.2 TYP 5.8 SEATING PLANE PIN 1 ID AREA A 0.1 C 6X 1.27 8 1 2X 3.81 5.0 4.8 NOTE 3 4 5 B 8X 4.0 3.8 NOTE 4 0.51 0.31 0.25 1.7 MAX C A B 0.25 TYP 0.10 SEE DETAIL A 5 4 EXPOSED THERMAL PAD 0.25 GAGE PLANE 2.34 2.24 8 1 0 -8 0.15 0.00 1.27 0.40 DETAIL A 2.34 2.24 TYPICAL 4218825/A 05/2016 PowerPAD is a trademark of Texas Instruments. NOTES: 1. All linear dimensions are in millimeters. Any dimensions in parenthesis are for reference only. Dimensioning and tolerancing per ASME Y14.5M. 2. This drawing is subject to change without notice. 3. This dimension does not include mold flash, protrusions, or gate burrs. Mold flash, protrusions, or gate burrs shall not exceed 0.15 mm per side. 4. This dimension does not include interlead flash. Interlead flash shall not exceed 0.25 mm per side. 5. Reference JEDEC registration MS-012. www.ti.com EXAMPLE BOARD LAYOUT DDA0008A PowerPAD TM SOIC - 1.7 mm max height PLASTIC SMALL OUTLINE (2.95) NOTE 9 SOLDER MASK DEFINED PAD (2.34) SOLDER MASK OPENING 8X (1.55) SEE DETAILS 1 8 8X (0.6) SYMM (1.3) TYP (2.34) SOLDER MASK OPENING (4.9) NOTE 9 6X (1.27) 5 4 (R0.05) TYP METAL COVERED BY SOLDER MASK SYMM ( 0.2) TYP VIA (1.3) TYP (5.4) LAND PATTERN EXAMPLE SCALE:10X 0.07 MIN ALL AROUND 0.07 MAX ALL AROUND SOLDER MASK OPENING METAL SOLDER MASK OPENING METAL UNDER SOLDER MASK SOLDER MASK DEFINED NON SOLDER MASK DEFINED SOLDER MASK DETAILS 4218825/A 05/2016 NOTES: (continued) 6. Publication IPC-7351 may have alternate designs. 7. Solder mask tolerances between and around signal pads can vary based on board fabrication site. 8. This package is designed to be soldered to a thermal pad on the board. For more information, see Texas Instruments literature numbers SLMA002 (www.ti.com/lit/slma002) and SLMA004 (www.ti.com/lit/slma004). 9. Size of metal pad may vary due to creepage requirement. 10. Vias are optional depending on application, refer to device data sheet. If any vias are implemented, refer to their locations shown on this view. It is recommended that vias under paste be filled, plugged or tented. www.ti.com EXAMPLE STENCIL DESIGN DDA0008A PowerPAD TM SOIC - 1.7 mm max height PLASTIC SMALL OUTLINE (2.34) BASED ON 0.125 THICK STENCIL 8X (1.55) (R0.05) TYP 1 8 8X (0.6) (2.34) BASED ON 0.125 THICK STENCIL SYMM 6X (1.27) 5 4 METAL COVERED BY SOLDER MASK SYMM (5.4) SEE TABLE FOR DIFFERENT OPENINGS FOR OTHER STENCIL THICKNESSES SOLDER PASTE EXAMPLE EXPOSED PAD 100% PRINTED SOLDER COVERAGE BY AREA SCALE:10X STENCIL THICKNESS SOLDER STENCIL OPENING 0.1 0.125 0.150 0.175 2.62 X 2.62 2.34 X 2.34 (SHOWN) 2.14 X 2.14 1.98 X 1.98 4218825/A 05/2016 NOTES: (continued) 11. Laser cutting apertures with trapezoidal walls and rounded corners may offer better paste release. IPC-7525 may have alternate design recommendations. 12. Board assembly site may have different recommendations for stencil design. www.ti.com MECHANICAL DATA NDZ0007B TA07B (Rev E) www.ti.com IMPORTANT NOTICE AND DISCLAIMER TI PROVIDES TECHNICAL AND RELIABILITY DATA (INCLUDING DATASHEETS), DESIGN RESOURCES (INCLUDING REFERENCE DESIGNS), APPLICATION OR OTHER DESIGN ADVICE, WEB TOOLS, SAFETY INFORMATION, AND OTHER RESOURCES "AS IS" AND WITH ALL FAULTS, AND DISCLAIMS ALL WARRANTIES, EXPRESS AND IMPLIED, INCLUDING WITHOUT LIMITATION ANY IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT OF THIRD PARTY INTELLECTUAL PROPERTY RIGHTS. These resources are intended for skilled developers designing with TI products. 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