REN semiconductors} Bere eee Lc erie ae Lot Ste FEATURES Low External Component Count Low Quiescent Current (7 mA typical! at 4.8V) Excellent Voltage and Temperature Stability High Output Drive Capability Consistent and Repeatable Performance Precision Internal Voltage Stabilisation Time Shared Error Pulse Expansion Balanced Deadband Control 14 lead D.I.L. Schmitt Trigger Input Shaping Reversing Relay Output (D.C. Motor Speed Control) DESCRIPTION The ZN409CE is aprecision monolithic integrated circuit designed particularly for pulse-width position servo mechanisms used in all types of contro! applications. The low number of components required with the ZN40SCE, together with its low power consumption, make this integrated circuit ideal for use in model aircraft, boats and cars where space, weight and battery life are at a premium. The amplifier will operate over a wide range of repetition rates and pulse widths and is therefore suitable for the majority of systems. The ZN409CE can also be used in motor speed control circuits. PNP PULSE LOGIC POSITIVE BASE INPUT QE AOBAND EXPANSION EARTH SUPPLY ORIVE OUTPUT 1%] [13 | 12 Tl 19 fg a! ! 7 15 224 | [3.5 vours {2.2 vouTs \ | INPUT SCHMITT IREGULATOR|PIN 2/[REGULATOR wD ) ! DEAOBAND PULSE : OUTPUT | EXPANSION} GATE ' ' 4 | | _| TRIGGER | \ MONO - 4 | | STABLE T f | ! | putse loiection } ouTeuT | | $ ECTION uT PUT OMPARISON BI STABLE GATE TIMING - MONO - STABLE \ i | 1 7 in Lz] LJ La] is! ts]t(i YS TIMING REGULATED POTENTIOMETER OIRECTION PNP OUTPUT OuTePut COMPONENTS 22 VOUT & TIMING OUTPUT BASE EARTA OUTPUT REFERENCE ORIVE 6180/09 Fig.1. SYSTEM DIAGRAM oeZN409CE ABSOLUTE MAXIMUM RATINGS Supply Voltage _ Package Dissipation - Operating Temperature Range .. Storage Temperature Range CHARACTERISTICS (Vs = 5V. At 25C ambient temperature unless otherwise stated). 6.5 Volts "300 Milliwatts -20C to +65C -. -65C to +150C Parameter Min. | Typ. | Max. | Unit Conditions Input threshold (lower) 1.15 | 1.25 | 1.35 | V Pin 14 Input threshold (upper) 1.4, 1.5 | 1.6} V Pin 14 Ratio upper/lower threshold 1:1 | 1:2 | 1:3 -10 to +65C Input resistance 20 | 27 | 35 | kQ Input current 350 | 500 | 650 | uA Regulator voltage 2.1 | 2.2 | 2.3 | V 10 to + 65C, 1.3 mA load current Regulator supply rejection ratio 200 | 300; Vs = 3.5 to 6.5V RSRR = dVin dVout Monostable linearity _ 3.5 4.0 | % +45, Rp = 1.5 k0 Ry = 12kQ Monostable period temperature {+0.01; | %/C| Excluding Rt, Cr. coofficiont Rp = 1.6kQ, Ry = 12kQ (potentiometer slider set mid-way) Output Schmitt deadband +1 [+1.5! +3 | us Ce = 0.47 pF Minimum output pulse 2.5 | 35 | 4.5 | ms | Ce = 0.47 uF, Re = 180 kD Error pulse for full drive 70 | 100 | 130 | us 15 ms repetition rate Ce = 0.47 uF, Re = 180 kQ Total deadband +3.5;| +5 |+6.5] us Cp = 1000 pF P.N.P. drive 40 55 70 | mA | T= 25C 35 50 65 | mA | T=-10C Output saturation voltage | 300 | 400 | mV | I, = 400mA Direction bistable output 2 2.8 | 3.6 | mA Supply voitage range i 3.5 5 6.5 1 V Supply current 4.6 | 6.7 | 10 | mA | Quiescent Total external currant from regulator| 1.3 | mA | Vs = 3.5V Paak voltage V zy (with respect | 0.7 = 25 to 2V regulated voltaga) 0.5 v to 7 Orc LN409CE. Page 2 Ee -OPERATING AND DESIGN NOTES 1. SERVO APPLICATION ZN409CE Component Function Releanee Value Comments Monostable Timing Components Rr 100 kO Note 1(e) Cr 0.1 LF Potentiometer and Timing Reference Ro 1.5 kQ Note 1(e) Components 5 kQ Note 1(g) Ry 4.7 kQ Note 1 (e) Pulse Expansion CE 0.47 uF Note 1(d) RE 180 kQ 11Q Motor 150 kQ 8Q Motor Deadband (Note 1(c)) Cy 1000 pF 11Q Motor 1500 pF 89 Motor Dynamic Feedback Re 330 kQ Rp 330 kQ Note 1 (f) Ro 1.2kQ Input Coupling Co 2.2 uF Note 1(b) Motor Decoupling Co 0.01 uF C3 0.01 uF R.F. Decoupling C, 0.1 BF Note 1 (h) Drive Transistors T1, T2 Note 1(i) (a) Introduction In the standard servo application the displacement of a control stick varies the pulse width of a timing circuit and many such pulses are time division multiplexed and typically modulate a 27 MHz transmitter. A receiver then decodes the transmitted signal and reconstitutes an independent train of pulses for each servo channel. The servo shown in Fig. 2 consists of the ZN409CE integrated circuit, several external components, a power amplifier consisting of two external PNP transistors and two on-chip NPN transistors which farm a bridge circuit to drive the d.c. motor. The motor drives a reduction gear box which has a potentiometer attached to the output shaft. This potentiometer in association with R, and the timing components Cy and Ry controls the pulse width of the ZN409CE, Page 3ZN409CE Vs Re CE qT, Ake = oT y= cons c joe! R 14 13.~12 1 10 9 8 C B 3 PIN? ZN409CE MOTOR ep <Rp GEARING 1 2 3 s 5 6 7 Li R, LJ Ld ate R. | Ce AVY Cr Rt Ry Rp >Re To 6151/09 Fig. 2. SERVO SYSTEM USING THE ZN409CE timing monostable. The input pulse is compared with the monostable pulse in a comparison circuit and one output is used to enable the correct phase of an on-chip power amplifier. The other output from the pulse comparison circuit drives the pulse expansion circuit (Ce, Re) via the deadband circuit (Cp). Thus any difference between the input and monostable pulses is expanded and used to drive the motor in such a direction as to reduce this difference so that the servo takes up a position which corresponds to the position of the control stick. (b) Input Circuit The ZN409CE operates withipositive going input pulses which can be coupled either directly or via a capacitor to pin 14. The advantage of a.c. coupling is that should a fault occur in the multiplex decoder which causes the input signal to become a continuous positive level, the servo will remain In its last quiescent position, whereas with direct coupling the servo output arm will rotate continuously. A nominal 27 kQ resistor is shunted across the input on chip to provide d.c. restoration of the input signal when a.c. coupling is used. The active input circuit is a Schmitt trigger which allows the servo to operate consistently with slow input edges and supplies the fast edge required by the trigger monostable independent of input edge speed. ZN409CE, Page 4ZN409CE Vee LIN 02 CONDUCTS of 50. PIN 14 358upAP ee SCHMITT Lc TRIGGER Wk LW" fh 27K 15K NM D A . 78yA [- = Te EL AMP O-7 ese 27k VIN Dy i Veo (4-8Y) | CONDUCTS t 50f 6152 6153 INPUT CIRCUIT INPUT CHARACTERISTICS Fig. 3. The input circuit and its V/! characteristic are shown above. D, and Dz are the parasitic substrate and isolation diodes associated with the input resistors. Itis advisable that the pulse input amplitude should not fall below OV nor exceed the supply voltage Voc in order to prevent these diodes fram conducting, although a small amount of conduction will not cause the circuit to malfunction. When a.c. coupling is used the value of C, should be chosen to give a pulse droop not exceeding 0.3 volts | 0O.3WMAX) | a Pp Fig. 4. INPUT WAVEFORMS ZN4IO9CE, Page 5ZN409CE Assuming that the input signal swings between OV and V, and taking the input chord resistance R;, of 13 kQ the droop fora pulse of duration t, msec willbe: t, (msec) Vt Pp Va=@ s z volts Co (nF) cr tio Rig (KQ) For a nominal pulse width of 1.5 msec and vg equal to 0.3 volts the required minimum value of Cc can be found as follows: 4.8.1.5 C. = _ C03. 13 A nominal value of 2.2 uF is chosen (Nearest preferred value). @ = 1.85 uF lf it is required to operate the servo with reduced input pulse amplitude the input pulse should exceed the upper Schmitt threshold voltage of 1.5 volts by a reasonable margin and a minimum input pulse amplitude of 2.4 volts is recommended. (c) Deadband Circuit The function of the deadband circuit is to provide a small range of output shaft position about the quiescent position where the difference pulse does not drive the motor. This is necessary to eliminate hunting around the quiescent position caused by servo inertia and overshoot. The minimum deadband required is also a function of the pulse expansion characteristics and dynamic feedback component values. 15V INTERNAL SUPPLY PULSE EXPANSION CIRCUITRY Uu DIFF ERENCE PULSE _ . | INPUT | SHORT PULSE ! |; ~ LONG PULSE t T 1-5V prey ~~ Lj b= To Vge!75) Pope wanna nb -- 0 t 1+ { COLLECTOR - T2 tq 6156 Fig. 5. DEADBAND CIRCUIT AND WAVEFORMS ZN409CE, Page 6ZN409CE When the difference pulse 1s applied T, turns off and the base of T2 rises on an exponential waveform with a time constant of 4.7kQ x Cp. If the difference pulse is small the potential reached on the base of T is insufficient to turn Tz on and no output results. The pulse expansion circuit has a built in deadband of 1.5 psec with Ce = 0.47 uF and this must be added to the deadband caused by Cp to obtain the total Ty. Ty = 1.5 + ty usec ty is found from the exponential equation. Voe= Vy 11 ___ be [ 00 Soca) | Vv ty = Cp. 4.7 loge (-) 1~*be = 3.3 Cp usec (Cp in nF) (Taking V, = 1.5 volts and V,,,, = 0.75 volts) Thus with Cp equal to 1000 pF (1 nF) ty = 3.3 usec and Ty = 4.8 usec. The mechanical deadband @d depends on the chosen sensitivity S,; of the servo and in the usual! radio control application a +500 usec input pulse variation causes +50 rotation, i.e.S; = 10 psec per degree. 2.T . . Thus Od = S d degrees (Ty in usec. S, in psec per degree). 1 Thus a value for Ty of 5 usec provides a mechanical deadband @d of 1. And generally : _ 2. 1.5 + ty) = = 34+ 6.6C i Od = SH 66 *0 degrees Co in nF. S; S, in usec per degree. @d ZN409CE, Page 7ZN409CE D.C. motors need a certain amount of drive to overcome static friction and the minimum output pulse obtained from this form of pulse expansion characteristic is chosen to ensure that the motor will rotate when driven. A linear initial pulse expansion characteristic would result in the motor remaining stationary and drawing full stall current for small drive periods. If the motor needs 2 msec of drive at a repetition rate of 20 msec to cause rotation, this is equivalent to an average drain of 50 mA for a 0.5A stall current. This is many times more than the quiescent current of the ZN40S8CE (7 mA) and could considerably reduce flying time for the standard battery operated airborne multichannel radio control system. This effect also causes an annoying buzz from the motor and gearbox. The use of the Schmitt trigger removes these two deficiencies. The value of t,,;,, is determined by the Schmitt trigger hysteresis and the exponential waveform on C, in the following equation. Vi = (Veo V0) ( 1 -exp [z]) because V,, is small the following linear relationship is sufficiently accurate. (Vee~Vi) CeRe comin _ Vu min (Vec-Vi) For nominal operation Voc = 4.8V; V,_ = 1.5V; Vy = 0.12V and: CeRe Ce in pF min % ~3q msec {stink and for Ce = 0.47 uF and Re = 180 kQ, t,,;, = 3.5 msec. Vy = t .CeRe msec it can be seen from the simple equation that t,,;,, is dependent on Vcc, and t,,;, will increase with reducing Veg. This variation is put to good use to maintain the initial motor drive, Vee X tmin reasonably constant over the operating voltage range of 3.5 to 6.5 volts. When the pulse expansion drive is increased above the minimum value the output pulse increases from t,,;, almost linearly until full pulse expansion is reached, i.e. when the output pulse width equals the input pulse repetition rate. The pulse expansion will be almost linear provided that the current source | does not saturate, i.e. provided that C_ is not discharged to almost zero volts. Ideally the current source should saturate when full motor drive is obtained but due to component tolerances it is usual to allow some margin to ensure that full motor drive can be obtained. If a margin is allowed, an extended pulse expansion characteristic results (shown dotted in Fig. 6) and if this is excessive it can lead to the servo exhibiting an underdamped characteristic causing jittering or hunting. Thus for full pulse expansion the voltage on C_e should discharge from its quiescent value of . 5V to 0.75 volts. Thus with |; = 3 mA for the current source: 1.5-0.75 Ig te CE Ce=4. ty uF (t, in msec) For t, = 0.1 msec, a value of 0.47 uF was chosen for Ce. ZN409CE, Page 9ZN409CE (d) Pulse Expansion Vs . OUTPUT PULSE WIOTH 4 t max RE tmin +1 te d DIFFERENCE SL PULSE EXPANSION PULSE WIDTH PULSE SCHMITT TRIGGER ' EXPANSION m ORIVE Ce \ Te ] t max 6158 Fig. 6. PULSE EXPANSION CIRCUIT AND CHARACTERISTIC A schematic of the pulse expansion circuit is shown in Fig. 6. In the quiescent state with no drive the Schmitt trigger input is biased via Re and takes up a level just above the lower threshold V. A drive pulse causes a current I_ to be switched on for the duration of the pulse and this discharges C_ linearly with time. Thus, at the end of the pulse the voltage on C_ depends on the duration of the pulse. If the pulse is narrow and just causes the potential on C, to fall to V_ the Schmitt trigger will switch to the upper threshold V,, and at the end of the drive pulse C, will start to charge to Vy, with a time constant C;-R_. When the potential on C_ reaches Vy, the Schmitt will switch to V_ and Ce will discharge to the quiescent level. The output drive is taken from the Schmitt output. INPUT WAVEFORM MONOSTABLE DEADBAND | | f | | PULSE EXPANSION DRIVE PULSE EXPANSION WAVEFORM SCHMITT OUTPUT DRIVE 6159 Fig. 7. PULSE EXPANSION TIMING DIAGRAM ZN409CE, Page 8ZN409CE Fig. 8. PULSE EXPANSION WAVEFORM If t. is the maximum motor drive pulse length required, i.e. equal to the input pulse repetition period for full pulse expansion, and the mean value of the potential on Cis taken as 1.2 volts, then: t, ty; dv = Seni (Vee -1.2) And for the discharge period t,: dv = le. te Ce t, t.,; Re= Seni (Vee -1.2) e For nominal values of Veg = 4.8V andl, =3mA t,-t Re= 1.2 te = tmin) kQ te and for tp = 20 msec, tmin = 3.5 msec, t, = 0.1 msec, Re = 180 kQ (Nearest preferred value). (e) Monostable Timing 22V PIN 2 ' 22V ct PIN | a l NL e- J Rp > ~ P Ry THROUGH R2 TO PIN 3 _- OV + OY 6162/09 Fig. 9. MONOSTABLE TIMING CIRCUIT AND WAVEFORM ZN409CE, Page 10ZN409CE The leading edge of the input waveform triggers the timing monostable by opening switch S,. C, then charges until the differential amplifier detects that the timing waveform potential has fallen to V,, the potential on the potentiometer wiper and switch S, is closed to terminate the timing pulse. Thus the monostable period is determined by the setting of the potentiometer wiper. In the standard application the servo centre position pulse width is 1.5 msec with a range of +50 rotation at 10 usec per degree. Thus the 2.0 msec maximum monostable period trono(max) corresponds to a potentiometer setting of 200 (for a linear relationship) and since the potentio- meter has a total rotation of approximately 270 and the maximum allowable swing on pin 3 is specified as 0.5 volt, the value of C;Ry can be calculated as follows: 0.5 2 tmono(max) Cy+Ry CyRy = 4. tmona(max) Thus if trono(max) = 2 msec, CpRy = 8 msec. The optimum value of Ry is 100 kM due to the design of the on-chip monostable circuit, giving Cr = 0.1 uF (nearest preferred value). Rr = 100 kQ Cr+ = 0.1 uF The value of R, can now be calculated from the actual voltage swing with a potentiometer setting of Op = 200 and @max = 270. 224 POTENTIOMETER SET AT 200 EQUIVALENT CIRCUIT Fig. 10 Thus from the equivalent circuit Vin (Veco- Vm) 200 RR + 70 R 270 + 1" 2970 where V_, is calculated from the actual values of C; and Ry chosen using the relationship i Vo = 2.0 . tmono(max) m _ CrRy since Cy = 0.1 uF (nearest preferred value) was chosen with Ry = 100 kQ, V,, = 0.4V and hence R,=3.1R, if Ro = 1.5kQ then Ry = 4.7 kQ. ZN409CE, Page 11ZN409CE (f) Dynamic Feedback Without dynamic feedback in the standard application the inertia of the motor and gearbox causes the servo output shaft to overshoot the set position which results in the servo hunting. If the deadband was widened to stop this effect an unacceptably large deadband would result and the servo would still be underdamped. The dynamic feedback circuit utilises the motor back emf (which is proportional to motor speed) and feeds back a proportion of this signal to the wiper of the potentiometer. The phase of the feedback signal is chosen to modify the potential on the wiper so that the monostable period is dynamically varied to reduce the motor drive as the servo output shaft approaches the set position and the values of the feedback resistors are chosen to achieve optimum settling characteristics. The value for R- and Rg of 330 kQ will suit the normal type of servo mechanism, however if the servo is fairly fast this can be decreased to 300 kQ to minimise any tendency to overshoot. Where the servo is slow R- and Rg can be increased to 360 kM or 390 kQ. (g) Alternative Value of R, Although a 1.5 kQ. feedback potentiometer is the most common value of Rp, 5 kQ potentiometers are used in some servo mechanisms. In order to use this value with the ZN40SCE a 2.2 kQ resistor is usually connected across the potentiometer to maintain the values of Re and Rg at 330 kM and R, at 4.7 kQ. Ro is omitted. i.e. the wiper of the potentiometer is connected directly to Pin 3 of the ZN409CE. (h) R.F. Decoupling C, (typical value 0.1 uF) is only necessary where strong R.F. fields may affect the operation of the circuit. (i) Transistors T1 and T2 The external PNP transistors are usually selected for a low Vcg;gat) to obtain maximum output drive and the recommended types are the ZTX550 or ZTX750. Z2N409CE, Page 12ZN409CE 2. MOTOR SPEED CONTROL (a) Introduction In the motor speed control application the ZN409CE 1s used as a linear pulse width amplifier. The d.c. motor is driven via a power amplifier with a train of pulses whose mark/space ratio can vary between zero and one to control the motor speed from zero to maximum. The ZN409CE operates 80 240/242 ZTX $02 fen 502 \ 1 6-12 120.0) | BATTERY A I ! ie he SL 4s 5 OR 6 2N3055 IN PARALLEL a 6165/09 Component Function Circuit Reference Value Monostable timing components Ry 100 kQ Cr 0.1 nF Potentiometer and timing reference R, 1kOQ components R, 4.7 kQ Pulse expansion Re 82 kQ \ Ce 1 Fr Deadband Cy 0.022 LF Input coupling Ce 2.2 uF Motor decoupling. See note 1(h) Cc, 0.01 uF Fig.11. HIGH PERFORMANCE PROPORTIONAL MOTOR SPEED CONTROL CIRCUIT AND RECOMMENDED COMPONENT VALUES ZN409CE, Page 13ZN409CE with fixed timing components and a fixed resistor replaces the position feedback potentiometer. The nominal monostable period represents zero motor speed and input pulses less than or greater than nominal drive the motor in the forward and reverse direction respectively. The motor direction is usually controlled by arelay operated from pin 4, the direction output. Pulse expansion components Ce and Reg are chosen to obtain the required relation between control stick deplacement and motor speed and it is usual to operate with a much larger deadband than that used in the servo application. Because high current motors are used to drive the wheels or propellors of model cars or boats a separate supply of 6 to 12 volts is used, and to provide reasonable running time between recharging the battery, a capacity of 1.2 Amp. hr. is usual. 1/4 scale cars with reasonable performance can be powered by a 5 amp stall current motor such as the Marx Monoperm (6 12 volts) driven from a single 2N3055 power transistor. However, if very high performance is required then five or six 2N3055 power transistors are used in parallel as shown in Fig. 11 to drive a 25 amp stall current motor. The Mabuchi RS54 operates from 6 to 8 volts and will provide a top speed of about 25 mphina 3 scale car. Acceleration is superb and the car wheels can be spun easily even on the best surfaces although the 1.2 amp hr. battery will need a full recharge after some ten minutes of racing. The motor and 2N3055 transistors dissipate a great deal of power especially at low speed and almost full stall current drive so the power transistors need to be mounted on a good heat sink such as the aluminium chassis of the car and a motor with crimped commutator connections rather than soldered connections is necessary since soldered connections have been seen to melt under stall conditions. The outputs from pins 9 and 5 of the ZN409CE integrated circuit are combined using two ZTX502 PNP transistors to provide a pulsed output whose mark/space ratio varies from 0 to 1 depending on the deflection of the control stick. This signal is then used to drive the motor via the power amplifier. The ZN40SCE has additional circuitry which performs the motor reversing function by taking the output from the direction bistable and provides either zero current or approximately 3 mA sink current at pin 4, depending on the state of the direction bistable. This current is amplified and used to drive the relay coil (100 mA) via the ZTX450 transistor thus controlling the motor direction via the relay changeover contacts. It is usual to have a relatively wide deadband and Cy, = 0.022 uF provides a deadband of about 14% (+7 degrees). i The pulse expansion compnents Ce and R_- are chosen to give full motor drive at about 90% full stick displacement and using the formulae derived earlier yields values of Ce = 1 uF, Re = 82 kN. The monostable timing component values remain unchanged at Cr = 0.1 uF, Rp = 100kQ. A 1 kQ potentiometer (Ro) can be used to set up the zero output condition with the control stick in its central position. ZN409CE, Page 14ZN409CE PACKAGE OUTLINE 2 J imino essomeyt 14 Lead Moulded D.I.L. Dimensions in millimetres ZN409CE, Page 15