RP504x Series
600 mA PWM/VFM Step-Down DC/DC Converter with Synchronous Rectifier
NO.EA-259-170620
1
OUTLINE
The RP504x is a low supply current CMOS-based PWM/VFM step-down DC/DC converter with sync hronous
rectifier featuring 600 mA*1 output current. Internally, a single converter consists of an oscillator, a reference
voltage unit, an error amplifier, a switching control circuit, a mode control circuit (RP504xxx1A/D), a soft-start
circuit, a Latch-type protection circuit, an under voltage lockout (UVLO) circuit a.nd switching transistors.
The RP504x is employing synchronous rectification for improving the efficiency of rectification by replacing
diodes with built-in switching transistors. Using synchronous rectification not only increases circuit performance
but also allows a de sign to reduce parts count.
Power controlling method can be selected from forced PWM control type or PWM/VFM auto switching control
type by inputting a signal to the MODE pin. In low out put current, forced PWM control switches at fixed frequency
rate in order to reduce noise. Likewise, in low output current, PWM/VFM auto switching control automatically
switches from PWM mode to VFM mode in order to achieve high efficiency.
Output voltage i s internally fixed t ype which allow s output voltages t hat range from 0.8 V to 3.3 V in 0.1 V step.
The output voltage accuracy is as high as ±1. 5% or ±18 mV.
Protection circuits included in the RP504x are overcurrent protection circuit and latch type protection circuit.
Overcurrent protection circuit supervises the inductor peak current in each switching cycle, and if the current
exceeds the LX current limi t (ILXLIM), it turns off P-channel Tr . Latch ty pe protectio n circui t latch es the built-in driver
to the OFF state and stops t he operation of the step-d own DC/DC conv erter if the overcurrent status cont inues or
VOUT continues being the half of the sett ing voltage for equal or longer than p rotection delay tim e (tprot). To cancel
the latch type protection circuit, select the standby mode or the active mode with the CE pin, or drop the power
supply voltage below the UVLO detector threshold.
The RP504x is offered in 6-pin DFN(PLP)1216-6 F, 6-pin DFN1616-6B and 5-pin SOT-23-5 packages which
achieve the smallest possible footprint solution on boards where area is limited.
*1 This is an ap pr oximate value. The output cur rent is depen dent on conditions and extern al components.
RP504x
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FEATURES
• Supply Current ...................................................... Typ. 25 µA in VFM mode without any load
• Standby Current .................................................... Max. 5 µA
• Input Voltage Range ............................................. 2.3 V to 5.5 V (VOUT ≥ 1.0 V)
• Output Voltage Range ........................................... 0.8 V to 3.3 V in 0.1 V step
• Output V oltage Accuracy ....................................... ±1.5% (VOUT ≥ 1.2 V), ±18 mV (VOUT < 1.2 V)
• Temperature-Drift Coefficient of O utput Voltage ... Typ. ±40 ppm/°C
• Oscillator Frequency ............................................. Typ. 2.25 MHz
• Oscillator Maximum Duty Cycle ............................ Min. 100%
• Built-in Driver O N Resistance ............................... Typ. Pch. 0.34 Ω, Nch. 0.43 Ω (VIN = 3.6 V)
• UVLO Detector Threshold ..................................... Typ. 2.0 V
• Soft Start T ime ...................................................... Typ. 0.15 ms
• LX Current Limit ..................................................... Typ. 900 mA
• Latch-type Protection Circu it ................................. Typ. 1.5 ms
• Auto-discharge Function ....................................... Only for RP504xxxxD
• Power Controlling M ethod ..................................... forced PWM cont rol or PWM/VFM auto switching control
• MODE Pin*1 ........................................................... “H”: forced PWM control,
“L”: PWM/VFM auto switching control
• Package*1 .............................................................. DFN1616-6B, DFN(PLP)1216-6F, SOT-23-5
*1 DFN(PLP)1216-6F, DFN16 16-6B: forced PWM control by pulling MODE pin “H” or PW M/VFM auto switc hing control by
pulling MODE pin “L”
SOT-23-5: forced PWM control for RP504xxxxC and PWM/VFM auto switching control for RP504xxxxB
APPLICATIONS
• Power source for battery-powered equi pment.
• Power source for hand-held communication equipment, cameras, VCRs, camcorders.
• Power source for HDD, portable equipm ent.
RP504x
NO.EA-259-170620
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SELECTI ON GUIDE
The set output voltage, the package type, the MODE control pin function and the auto-discharge*1 function
are user-selectable o pt i ons.
Product Name
Package
Quantity per Reel
Pb Free
Halogen Free
RP504Kxx1$-E2
DFN(PLP)1216-6F
5,000 pcs
Yes
Yes
RP504Lxx1$-TR
DFN1616-6B
5,000 pcs
Yes
Yes
RP504Nxx1$-TR-FE
SOT-23-5
3,000 pcs
Yes
Yes
xx: Specify the set output v ol t age (V SET) within the range of 0.8 V (08) to 3.3 V(33) in 0.1 V st eps.
Refer to the section of PACKAGE INFORMATION for detailed information.
$: Specify the package type, the MODE control pi n function and the auto-discharge function.
$ Package
MODE Control Pin Function
Auto-discharge
Function
MODE Pin
Power Controlling Method
A DFN1616-6B Yes “H”: forced PWM
“L”: PWM/VFM aut o switching control No
DFN(PLP)1216-6F
B SOT-23-5 No PWM/VFM auto switching control No
C
SOT-23-5
No
forced PWM control
No
D DFN1616-6B Yes “H”: forced PWM control
“L”: PWM/VFM aut o switching control Yes
DFN(PLP)1216-6F
*1 Auto-dischar ge function quickly lo wers the output voltage t o 0 V, when the chip enable signal is s witched from the
active mode to the standby mode, by releasing the electrical charge accumulated in the ex ternal capacitor.
*2 0.05 V step is also available as a c ustom code.
RP504x
NO.EA-259-170620
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BLOCK DIAGRA MS
RP504xxxxA Block Diagram
RP504xxxxB Block Di agram
SWITCHING
CONTROL
CURRENT
PROTECTION
SOFT
START
VREF
Lx
V
OUT
V
IN
CE
GND
OSCILLATOR
PWM
CURRENT
FEEDBACK
RAMP
COMPENSATION
UVLO
MODE
CHIP
ENABLE
SWITCHING
CONTROL
CURRENT
PROTECTION
SOFT
START
VREF
Lx
V
OUT
V
IN
CE
GND
OSCILLATOR
PWM
CURRENT
FEEDBACK
RAMP
COMPENSATION
UVLO
MODE
CHIP
ENABLE
RP504x
NO.EA-259-170620
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RP504xxxxC Blo ck Di agram
RP504xxxxD Block Di agram
SWITCHING
CONTROL
CURRENT
PROTECTION
SOFT
START
VREF
Lx
V
OUT
V
IN
CE
GND
OSCILLATOR
PWM
CURRENT
FEEDBACK
RAMP
COMPENSATION
UVLO
MODE
CHIP
ENABLE
SWITCHING
CONTROL
CURRENT
PROTECTION
SOFT
START
VREF
L
X
V
OUT
V
IN
CE
GND
OSCILLATOR
PWM
CURRENT
FEEDBACK
RAMP
COMPENSATION
UVLO
MODE
CHIP
ENABLE
RP504x
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PIN DESCRIPTION
3
4
2
5
1
6
6
5
4
1
2
3
∗
1
3
5
4
2
DFN(PLP)1216-6F Pin Configurations DFN1616-6B Pin Configurations SOT-23-5 Pin Configurations
RP504Kxx1A, RP504Kxx1D: DFN(PLP)1 216-6F Pin Description
Pin No.
Symbol
Description
1
VIN
Input Pin
2 MODE
Mode Control Pin
(“H”: forced PWM control, “L”: PWM/VFM auto switching
control)
3
CE
Chip Enable Pin (Active-high)
4
VOUT
Output Pin
5
GND
Ground Pin
6
LX
LX Switching Pin
RP504Lxx1A, RP 504L xx1D: DFN1616-6B Pin Description
Pin No.
Symbol
Description
1
CE
Chip Enable Pin (Active-high)
2 MODE
Mode Control Pin
(“H”: forced PWM control, “L”: PWM/VFM auto switching
control)
3
VIN
Input Pin
4
LX
LX Switching Pin
5
GND
Ground Pin
6
VOUT
Output Pin
∗ The tab on the bottom of the package enhances thermal performance and is electrically connected to GND (substrate
level). It is recommended that the tab be connected to the ground plane on the board. If not, the tab can be left open.
RP504Nxx1B, RP504Nxx1C: SOT-23-5 Pin Description
Pin No.
Symbol
Description
1
VOUT
Output Pin
2
GND
Ground Pin
3
LX
LX Switching Pin
4
VIN
Input Pin
5
CE
Chip Enable Pin (Active-high)
RP504x
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ABSOLUTE MAXIMUM RATINGS
Absolute Maximum Ratings (GND = 0 V)
Symbol
Item
Rating
Unit
V
IN
V
IN
Input Voltage
−0.3 to 6.5
V
V
LX
L
X
Pin Voltage
−0.3 to V
IN
+0.3
V
V
CE
CE Pin Input Voltage
−0.3 to 6.5
V
V
MODE
Mode Control P i n Voltage
−0.3 to 6.5
V
V
OUT
V
OUT
Pin Voltage
−0.3 to 6.5
V
ILX
LX Pin Output Current
900
mA
PD Power Dissipation
(Standard Land Pattern)*1
DFN(PLP)1216-6F
385
mW
DFN1616-6B
640
SOT-23-5
420
Tj
Junction Temperature Range
−40 to 125
°C
Tstg
Storage Temperature Range
−55 to 125
°C
*1 Refer to POWER DISSIPATION for detailed information.
ABSOLUTE MAXIMUM RATINGS
Electronic and mechanical stress
momentarily exceeded absolute maximum ratings may cause the permanent
damages and may degrade the life time and safety for both device and system using the device in the field. The
functional o peration at or over these absol ute maximum rat ings is not ass ured.
RECOMMENDED OPERATING CONDITIONS
Recommended Operating Conditions
Symbol
Item
Rating
Unit
VIN Operating Inp ut V ol tage
2.3 to 5.5 (V
OUT
≥ 1.0)
V
2.3 to 4.5 (V
OUT
< 1.0)
V
Ta
Operating Temperature Ra nge
−40 to 85
°C
RECOMMENDED OPERATING CONDITIONS
All of electronic equipment should be designed that the mounted semiconductor devices operate within the
recommended operating conditions. The semiconductor devices cannot operate normally over the recommended
operating conditions, even if when they are used over such conditions by momentary electronic noise or surge. And
the semiconductor devices may receive serious damage when they continue to operate over the recommended
operating conditions.
RP504x
NO.EA-259-170620
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ELECTRICAL CHARACTERISTICS
RP504xxx1A, RP504xxx1D Electrical Characteristics (Ta = 25°C)
Symbol
Item
Conditions
Min.
Typ.
Max.
Unit
VOUT Output Voltage VIN = VCE = 3.6 V
or VSET +1 V
V
OUT
≥ 1.2 V
x0.985
x1.015
V
VOUT < 1.2 V
−0.018
+0.018
∆VOUT/∆Ta
Output Voltage Temperature
Coefficient
−40°C ≤ Ta ≤ 85°C ±40 ppm/°C
fosc
Oscillator Frequency
VIN = VCE = 3.6 V or VSET +1 V
1.95
2.25
2.55
MHz
IDD1 Supply Current 1
V
IN
= V
CE
= 5.5 V, V
OUT
= V
SET
×
0.8
400 800 µA
IDD2 Supply Current 2 VIN = VCE = VOUT
= 5.5 V
V
MODE
= 0 V
25
40
µA
VMODE = 5.5 V
400
800
Istandby
Standby Current
VIN = 5.5 V, VCE = 0 V
0
5
µA
I
CEH
CE "H" Input Voltage
V
IN
= V
CE
= 5.5 V
−1
0
1
µA
I
CEL
CE "L" Input Voltage
V
IN
= 5.5 V, V
CE
= 0 V
−1
0
1
µA
IMODEH
Mode "H" Input Cur rent
VIN = VMODE = 5.5 V
−1
0
1
µA
IMODEL
Mode "L" Input Cur rent
VIN = 5.5 V, VMODE = 0 V
−1
0
1
µA
I
VOUTH
V
OUT
"H" Input Current *1
V
IN
= V
OUT
= 5.5 V, V
CE
= 0 V
−1
0
1
µA
IVOUTL
V
OUT
"L" Input Current
VIN = 5.5 V, VCE = VOUT = 0 V
−1
0
1
µA
ILXLEAKH
L
X
Leakage Current "H"
VIN = VLX = 5.5 V, VCE = 0 V
−1
0
5
µA
I
LXLEAKL
L
X
Leakage Current "L"
V
IN
= 5.5 V, V
CE
= V
LX
= 0 V
−5
0
1
µA
VCEH
CE "H" Input Voltage
VIN = 5.5 V
1.0
V
VCEL
CE "L" Input Voltage
VIN = 2.3 V
0.4
V
V
MODEH
Mode ”H” Input Vol tage
V
IN
= 5.5 V
1.0
V
V
MODEL
Mode ”L” Input Voltage
V
IN
= 2.3 V
0.4
V
RLOW
Nch On Resistance*2
VIN = 3.6 V, VCE = 0 V
30
Ω
RONP
On Resistance of Pch Tr.
VIN = 3.6 V, ILX = −100 mA
0.34
Ω
R
ONN
On Resistance of Nch Tr.
V
IN
= 3.6 V, I
LX
= −100 mA
0.43
Ω
Maxduty
Oscill at or M a xi m um Duty
Cycle
100 %
tstart
Soft-start Time
VIN = VCE = 3.6 V or VSET +1 V
150
310
µs
I
LXLIM
Lx Current Limit
V
IN
= V
CE
= 3.6 V or V
SET
+1 V
700
900
mA
tprot
Protection Delay Time
VIN = VCE = 3.6 V or VSET +1 V
0.5
1.5
5
ms
VUVLO1
UVLO Detector Threshold
VIN = VCE
1.9
2.0
2.1
V
V
UVLO2
UVLO Released Voltage
V
IN
= V
CE
2.0
2.1
2.2
V
All test items listed under ELECTRICAL CHARACTERISTICS are done under the pulse load condition (Tj ≈ Ta = 25°C) except
Output Voltage Temperature Coefficient.
Test circuit is "OPEN LOOP" and AGND = PGND = 0 V unless ot herwise specified.
*1 Only for RP504xxx1A/B/C with no auto-discharge
*2 Only for RP504xxx1D with auto-discharge
RP504x
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RP504xxxxB, RP504xxxxC Electrical Characteristics (Ta = 25°C)
Symbol
Item
Conditions
Min.
Typ.
Max.
Unit
VOUT Output Voltage VIN = VCE = 3.6 V
or VSET +1 V
V
OUT
≥ 1.2 V
x0.985
x1.015
V
VOUT < 1.2 V
−0.018
+0.018
∆VOUT/∆Ta
Output Voltage Temperature
Coefficient
−40°C ≤ Ta ≤ 85°C ±40 ppm/°C
fosc
Oscillator Frequency
VIN = VCE = 3.6 V or VSET +1 V
1.95
2.25
2.55
MHz
IDD1 Supply Current 1
V
IN
= V
CE
= 5.5 V,
VOUT = VSET × 0.8
400 800 µA
IDD2 Supply Current 2 VIN = VCE = VOUT
= 5.5 V
RP504xxx1B
25
40
µA
RP504xxx1C
400
800
Istandby
Standby Current
VIN = 5.5 V, VCE = 0 V
0
5
µA
I
CEH
CE "H" Input Voltage
V
IN
= V
CE
= 5.5 V
−1
0
1
µA
I
CEL
CE "L" Input Voltage
V
IN
= 5.5 V, V
CE
= 0 V
−1
0
1
µA
IVOUTH
V
OUT
"H" Input Current
VIN = VOUT = 5.5 V, VCE = 0 V
−1
0
1
µA
IVOUTL
V
OUT
"L" Input Current
VIN = 5.5 V, VCE = VOUT = 0 V
−1
0
1
µA
I
LXLEAKH
L
X
Leakage Current "H"
V
IN
= V
LX
= 5.5 V, V
CE
= 0 V
−1
0
5
µA
ILXLEAKL
L
X
Leakage Current "L"
VIN = 5.5 V, VCE = VLX = 0 V
−5
0
1
µA
VCEH
CE "H" Input Voltage
VIN = 5.5 V
1.0
V
V
CEL
CE "L" Input Voltage
V
IN
=2.3 V
0.4
V
RONP
On Resistance of Pch Tr.
VIN =3.6 V, ILX = −100 mA
0.34
Ω
RONN
On Resistance of Nch Tr.
VIN =3.6 V, ILX = −100 mA
0.43
Ω
Maxduty
Oscillator Maximum Duty
Cycle
100 %
tstart
Soft-start Time
V
IN
= V
CE
= 3.6 V or V
SET
+1 V
150
310
µs
ILXLIM
L
X
Current Limit
VIN = VCE = 3.6 V or VSET +1 V
700
900
mA
tprot
Protection Delay Time
VIN = VCE = 3.6 V or VSET +1 V
0.5
1.5
5
ms
V
UVLO1
UVLO Detector Threshold
V
IN
= V
CE
1.9
2.0
2.1
V
VUVLO2
UVLO Released Voltage
VIN = VCE
2.0
2.1
2.2
V
All test items listed under ELECTRICAL CHARACTERISTICS are done under the pulse load condition (Tj ≈ Ta = 25°C) except
Output Voltage Temperature Coefficient.
Test circuit is "OPEN LOOP" and AGND = PGND = 0 V unless ot herwise specified.
RP504x
NO.EA-259-170620
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OPERATI NG DESCRIPTIONS
OPERATION OF STEP-DOWN CONVERTER AND OUTPUT CURENT
The step-down DC/DC converter charges energy in the inductor when LX Tr. turns “ON”, and discharges the
energy from the inductor when LX Tr. turns “OFF” and operates with less energy loss, so that a lower output
voltage (VOUT) than the input voltage (VIN) can be obtained. The operation of the step-down DC/DC converter is
explained in the foll owing figures.
Pch Tr
L
Nch Tr
VIN
i1
VOUT
CL
i2
GND
T＝1/fosc
ton
toff
topen
ILmin
ILmax
IL
i1
i2
Figure 1. Basic Circuit
Figure 2. Inductor Current (IL) flowing through Inductor
Step1. P-channel Tr. turns “ON” and IL (i1 ) flows, L is charged with energy. At this moment, i1 increases from
the minimum inductor current (ILmin), which is 0 A, and reaches the maximum inductor current (ILmax)
in proportion to the on-t ime perio d (ton) of P-channel Tr.
Step2. When P-channel Tr. turns “OFF”, L tries to maintain IL at ILmax, so L turns N-channel Tr. “ON” and IL
(i2) flows into L.
Step3. i2 decreases gradually and reaches ILmin after the open-time period (topen) of N-channel Tr., and then
N-channel Tr. turns “OFF”. This is called dis cont i nuous current mode.
As the output current (IOUT) increases, the off-time period (tof f) of P-channel T r . runs out before IL reaches
ILmin. The next cycle starts, and P-channel Tr. turns “ON” and N-channel Tr. turns “OFF”, which means
IL starts incre asing from ILmin. This is called continuous current mode.
In the case of PWM mode, VOUT is maintained by cont rolli ng ton. During t he P W M mode, the os cillator f req uen cy
(fosc) is constantl y maintained.
As shown in Figure 2, when the step-down DC/DC operation is constant, ILmin and ILmax during ton of P-channel
Tr. would be the same as ILmin and ILmax during toff of the P-chan nel Tr .
The current differential between ILmax and ILmin is descri bed as ∆I.
∆I = ILmax − ILMIN = VOUT × topen / L = (VIN − VOUT) × ton / L ....................................... Equation 1
However,
T = 1 / fosc = ton + toff
Duty (%) = ton / T × 100 = ton × fosc × 100
topen ≤ toff
In Equation 1, “VOUT × topen / L” shows the amount of current change in “OFF” state. Also, “(VIN − VOUT) × ton /
L” shows the amount of current change at “ON” state.
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DISCONTINUOUS MODE AND CONTINUOUS MODE
As illustrated in Figure 3, when IOUT i s relatively small, topen < toff. I n this case, t he energy charged into L during
ton will be completel y discharged durin g toff, as a result , I LMIN = 0. This is called discontinuous m ode.
When IOUT is gradually increased, eventually topen = toff and when IOUT is increa sed further, eventually I LMIN > 0.
This is called continuous mode.
ILMAX
ILMIN
ton
toff
T = 1 / fosc
topen
IL
t
ILMAX
ILMIN
ton
toff
T = 1 / fosc
IL
ICONST
t
Figure 3. Discontinuous Mode
Figure 4. Continuous Mode
In the continuous mode, the solution of Equati on 1 i s described as tonc.
tonc = T × VOUT / VIN ............................................................................................................... Equation 2
When ton < tonc, it indic ates discontinuous mode, and when ton = tonc, i t indicates continuous mode.
RP504x
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TIMING CHA RT
1. Soft-start Time
Starting-up with CE Pin
The IC starts to operat e when the CE pin voltage (VCE) exceeds the threshold voltage. The threshold voltage
is preset between CE “H” input voltage (VCEH) and CE “L” input voltage (VCEL).
After the start-up of the IC, soft-start circuit starts to operate. Then, after a certain period of time, the
reference voltage (VREF) in the IC gradually increase s up to the specified value.
V
CEH
Soft-start Time
IC Internal Referenc e Voltage
V
CEL
Threshold Level
Lx Voltage
(V
CE
)
(V
REF
)
Soft-start Circuit
operation starts.
(V
LX
)
Depending on Power Supply,
Load Current, External Components
(V
OUT
)
Output Voltage
CE Pin Input Voltage
IC operates with PWM mode
during Soft-start time.
Soft-start time starts when soft-start circuit is activated, and ends when the reference voltage reaches the
specified voltage.
Soft start time is not always equal to the turn-on speed of the step -down DC/DC convert er . Please note that the
turn-on speed could be affected by the power sup ply capacit y, the output current, the induct ance valu e and t he
COUT value.
Starting-up with Power Supply
After the power-on, when VIN exceed s the UVL O rele ased volt age (VUVLO2), the IC starts to operat e. Then, soft-
start circuit starts to operate and after a certain period of time, VREF gradually increases up to the specified
value. Soft-start time starts when soft-start circuit is activated, and ends when VREF reaches the specified voltage.
Output Voltage
(V
OUT
)
Input Voltage
(V
IN
)
V
UVLO2
IC Internal Reference Voltage
(V
REF
)
V
UVLO1
Lx Voltage
(V
LX
)
V
SET
V
SET
Depending on Power Supply, Load Current,
External Components
Soft-start Time
IC operates with PWM mode during Soft-st a rt time .
Please note that the t urn-on speed of VOUT could be affected by the power supply capacity, the output current,
the inductance value, the COUT value and the turn-on speed of VIN determined by CIN.
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2. Under Voltage Lockout (UVLO) Circuit
If VIN becomes lower than VSET, the step-down DC/DC converter stops the switching operation and ON duty
becomes 100%, and then VOUT gradually drops according to VIN.
If the VIN becomes lower than the UVLO detector threshold (VUVLO1), the UVLO circuit starts to operate, VREF
stops, and P-channel and N-channel built-in switch transistors tur n “OFF”. As a result, VOUT drops a ccording to
the COUT capacitance value and the load.
To restart the operation, VIN needs to be higher than VUVLO2. The timi ng chart below shows t he voltage shifts of
VREF, VLX and VOUT when VIN value is varied.
Output Voltage
(V
OUT
)
Input Voltage
(V
IN
)
V
UVLO2
IC Internal Reference Voltage
(V
REF
)
V
UVLO1
Lx Voltage
(V
LX
)
V
SET
V
SET
Depending on Power Supply, Loa d Current,
External Components
Soft-start Time
Falling edge (operating) and rising edge (releasing) waveforms of VOUT could be affected by the initial voltage
of COUT and the output current of VOUT.
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3. Overcurrent Protection Circuit, Latch Ty pe P rotection Circuit
Overcurrent protecti on circuit supervi ses the inductor pea k current (the peak cu rrent flowin g through Pc h T r.) in
each switching cycle, and if the current exceeds the LX current limit (ILXLIM), it turns off Pch Tr. ILXLIM of the
RP504x is set to T yp.900 mA.
Latch type protect ion circuit lat ches the built-in driver to the OFF state and stops the operat ion of the step-down
DC/DC converter if the overcurrent status continues or VOUT continues being the half of the setting voltage for
equal or longer than prot ection delay time (t prot).
Please note that ILXLIM and tprot could be easily affected by self-heating or ambien t environment. If the VIN drops
dramatically or becomes unstable due to short-circuit, prot ect i on operation and tprot co ul d be aff ect ed.
Protection Delay Time (tprot)
Lx Current Limit (ILXlim)
Lx Current
Pch T r. Current
Lx Voltage
(VLX)
To release the latch type protection circuit, restart the IC by inputting "L" signal to the CE pin, or restart the IC
with power-on or make the supply voltag e l ower than VUVLO1.
The timing chart below shows the voltage shift of VCE, VLX and VOUT when the IC status is changed by the
following orders: VIN rising → stable operation → high load → CE reset → stable operation → VIN falling → VIN
recovering (UVLO reset) → stable operation.
(1)(2) If the large current flows through the circuit or if the IC goes into low VOUT condition due to short-circuit or
other reasons, the latch type protection circuit latches the built-in driver to “OFF” state after tprot. Then,
VLX becomes "L" and VOUT turns “OFF”.
(3) The latch type protection circuit is released by CE reset, which puts the IC into "L" once with the CE pin and
back into "H".
(4) The l at ch type protection circuit i s released by UVLO re set , which makes VIN lower than VUVLO1.
Input Voltage
(V
IN
)
V
SET
UVLO Detector Threshold (VUVLO1)
CE Pin
Input Voltage
(V
CE
)
V
SET
Threshold Level
Lx Voltage
(V
LX
)
V
SET
Output Voltage
(V
OUT
)
UVLO Released Voltage (V
UVLO2)
(1)
(2)
Soft-start Time
V
SET
Soft-start Time
Soft-start Time
Stable
Operation
Stable
Operation
Stable
Operation
Protection Delay Ti me
Protection Delay Ti me
UVLO Reset
CE Reset
Latch-type Protection
Latch-type Protection
(3)
(4)
RP504x
NO.EA-259-170620
15
APPLICATION INFORMATION
TYPICAL APPLICATION CIRCUIT
C
OUT
4.7µF
CE
V
IN
L
X
V
OUT
V
IN
C
IN
2.2µF
L 2.2µH
Load
GND
RP504N
Control
RP504N Typical Application Circuit: MODE Pin not included
COUT 4.7µF
CE
MODE
*1
V
IN
L
X
V
OUT
V
IN
C
IN
2.2µF
L 2.2µH
Load
GND
RP504L/K
Control
Control
RP504K/L Typical Application Circuit: MODE Pin included
*1
MODE = “H”: forced PWM control, MODE = “L”: PWM/VFM auto switching control
Recommended Components
Symbol Capacitance Type Manufacturer
CIN
2.2 µF
Ceramic Capacitor
C1608JB0J225K(TDK)
2.2 µF x 2
C1005JB0J225K (TDK)
JMK105BJ225MV (Taiyo Yuden)
4.7 µF
C1005X5R0J475M (TDK)
JMK105BJ475MV (Taiyo Yuden)
COUT 4.7 µF Ceramic Capacitor
C1608JB0J475K (TDK)
GRM188B30J475KE18 (Murata)
L 2.2 µH Inductor
MIPSZ2520D2R2 (FDK)
MIPS2520D2R2 (FDK)
MLP2520S2R2M ( T DK)
VLS252010T-2R2M (TDK)
RP504x
NO.EA-259-170620
16
OUTPUT CURRENT AND SELECTION OF EXTERNAL COMPONENTS
The following equati ons explain the relat ionship between output cu rrent and peripheral co mponents used in t he
diagrams in TYPICAL APPLICATIONS.
Ripple Current P-P value is described as IRP, ON resistance of P-channel Tr. is described as RONP, ON
resistance of N-channel Tr. is described as RONN, and DC resistor of t he induct or is described as RL.
VIN = VOUT + (RONP + RL) × IOUT + L × IRP / ton .............................................................. Equation 3
Second, when P-ch annel Tr. is “OFF” (N-channel Tr. Is “ON”), the following equation is s atisfied.
L × IRP / toff = RONN × IOUT + VOUT + RL × IOUT ............................................................... Equation 4
Put Equation 4 into E quation 3 to solve ON duty of P-channel Tr . (DON = ton / (toff + ton)):
DON = (VOUT + RONN × IOUT + RL × IOUT) / (VIN + RONN × IOUT − RONP × IOUT) ................... Equation 5
Ripple Current is described as follows:
IRP = (VIN − VOUT − RONP × IOUT − RL × IOUT) × DON / fosc / L ......................................... Equation 6
Peak current that flows through L, and LX Tr. is descri bed as follows:
ILXMAX = IOUT + IRP / 2 .................................................................................................... Equation 7
Consider ILXMAX when setting conditions of i nput and output, as well as sel ecti ng the external components.
The above calculation formulas are based on t he ideal operation of the I CS in continuous mode.
RP504x
NO.EA-259-170620
17
TECHNICAL NOTES
The performance of power supply circuit s using this IC largely de pends on the peripher al circuits. Please be v ery
careful when setting the peripheral parts. When designing the peripheral circuits of each part, PCB patterns, and
this IC, please do not exceed the rated values (Voltage, Current, P ower).
• Ensure the VIN and GND lines are sufficiently robust. A large switching current flows through the GND lines,
the VDD line, the VOUT line, an inductor, and LX. If their impedance is too high, noise pickup or unstable
operation may result. Set the external components as close as possible to the IC and minimize the wiring
between the components and the IC, especially between a capacitor (CIN) and the VIN pin. The wiring between
VOUT and load and between L and VOUT should be separated.
• Choose a low ESR ceramic capacitor. The capacitance of CIN should be more than or equal to 2.2 µF. The
capacitance of a capa citor (COUT) should be between 4.7 µF to 10 µF.
• The Inductance value should be set within the range of 2.2 µH to 4.7 µH. However, the inductance value is
limited by output voltage. Refer t o the tab le below. Th e phase com pensati on of this IC i s desig ned accordin g
to the COUT and L values. Choose an inductor that has small DC resistance, has enough allowable current
and is hard to cau se magnetic saturatio n. If the inductance value of an inductor i s ex tremely small, t he peak
current of LX may increase. The increased LX peak current reaches “LX limit current” to trigger overcurrent
protection circuit even if the load current i s l ess than 600 mA.
• Overcurrent protect ion circuit, Latch-type protection circuit may be affected by self-heating and heat radi ation
environment.
PCB LAYOUT
RP504Nxx1B/C (PKG: SOT-23-5) typical board layout
Topside
Backside
RP504x
NO.EA-259-170620
18
RP504Lxx1A/D (PKG: DFN1616-6B) typical board lay<