the uc1637 is a pulse width modulator circuit intended to be used for a variety of pwm motor drive and amplifier applications requiring either uni-directional or bi- directional drive circuits. when used to replace conventional drivers, this circuit can increase efficiency and reduce component costs for many applications. all necessary circuitry is included to generate an analog error signal and modulate two bi-directional pulse train outputs in proportion to the error signal magnitude and polarity. this monolithic device contains a sawtooth oscillator, error amplifier, and two pwm comparators with 100ma output stages as standard features. protection circuitry includes under-voltage lockout, pulse-by-pulse current limiting, and a shutdown port with a 2.5v temperature compensated threshold. the uc1637 is characterized for operation over the full military temperature range of -55c to +125c, while the UC2637 and uc3637 are characterized for -25c to +85c and 0c to +70c, respectively. switched mode controller for dc motor drive uc1637 UC2637 uc3637 block diagram single or dual supply operation 2.5v to 20v input supply range 5% initial oscillator accuracy; 10% over temperature pulse-by-pulse current limiting under-voltage lockout shutdown input with temperature compensated 2.5v threshold uncommitted pwm comparators for design flexibility dual 100ma, source/sink output drivers supply voltage ( vs) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20v output current, source/sink (pins 4, 7) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 500ma analog inputs (pins 1, 2, 3, 8, 9, 10, 11 12, 13, 14, 15, 16) . . . . . . . . . . . . . . . . . . . . . . . vs error amplifier output current (pin 17) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20ma oscillator charging current (pin 18). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -2ma power dissipation at t a = 25c (note 2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1000mw power dissipation at t c = 25c (note 2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2000mw storage temperature range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -65c to +150c lead temperature (soldering, 10 seconds). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +300c note 1: currents are positive into, negative out of the specified terminal. note 2: consult packaging section of databook for thermal limitations and considerations of package. features absolute maximum ratings (note 1) description 6/97
uc1637 UC2637 uc3637 package pin function function pin +v th 1 c t 2 -v th 3 a out 4 -v s 5 n/c 6 +v s 7 b out 8 +b in 9 -b in 10 -a in 11 +a in 12 +c/l 13 -c/l 14 shutdown 15 n/c 16 +e/a 17 -e/a 18 e/a output 19 i set 20 plcc-20, lcc-20 (top view) q, l packages electrical characteristics: parameter test conditions uc1637/UC2637 uc3637 units min typ max min typ max oscillator initial accuracy t j = 25c (note 6) 9.4 10 10.6 9 10 11 khz voltage stability v s = 5v to 20v, v pin 1 = 3v, v pin 3 = -3v 57 57% temperature stability over operating range (note 3) 0.5 2 0.5 2 % +v th input bias current v pin 2 = 6v -10 0.1 10 -10 0.1 10 m a -v th input bias current v pin 2 = 0v -10 -0.5 -10 -0.5 m a +v th, -v th input range +v s -2 -v s +2 +v s -2 -v s +2 v error amplifier input offset voltage v cm = 0v 1.5 5 1.5 10 mv input bias current v cm = 0v 0.5 5 0.5 5 m a input offset current v cm = 0v 0.1 1 0.1 1 m a common mode range v s = 2.5 to 20v -v s +2 +v s -v s +2 +v s v open loop voltage gain r l = 10k 75 100 80 100 db slew rate 15 15 v/ m s unity gain bandwidth 2 2 mhz cmrr over common mode range 75 100 75 100 db psrr v s = 2.5 to 20v 75 110 75 110 db connection diagram unless otherwise stated, these specifications apply for t a = -55c to +125c for the uc1637; -25c to +85c for the UC2637; and 0c to +70c for the uc3637; +v s = +15v, -v s = - 15v, +v th = 5v, -v th = -5v, r t = 16.7k w , c t = 1500pf, t a =t j. dil-18 (top view) j or n package soic-20 (top view) dw package 2
electrical characteristics: parameters test conditions uc1637/UC2637 uc3637 units min typ max min typ max error amplifier (continued) output sink current v pin 17 = 0v -50 -20 -50 -20 ma output source current v pin 17 = 0v 5 11 5 11 ma high level output voltage 13 13.6 13 13.6 v low level output voltage -14.8 -13 -14.8 -13 v pwm comparators input offset voltage v cm = 0v 20 20 mv input bias current v cm = 0v 2 10 2 10 m a input hysteresis v cm = 0v 10 10 mv common mode range v s = 5v to 20v -v s +1 +v s -2 -v s +1 +v s -2 v current limit input offset voltage v cm = 0v, t j = 25c 190 200 210 180 200 220 mv input offset voltage t.c. -0.2 -0.2 mv/c input bias current -10 -1.5 -10 -1.5 m a common mode range v s = 2.5v to 20v -v s +v s -3 -v s +v s -3 v shutdown shutdown threshold (note 4) -2.3 -2.5 -2.7 -2.3 -2.5 -2.7 v hysteresis 40 40 mv input bias current v pin 14 = +v s to -v s -10 -0.5 -10 -0.5 m a under-voltage lockout start threshold (note 5) 4.15 5.0 4.15 5.0 v hysteresis 0.25 0.25 mv total standby current supply current 8.5 15 8.5 15 ma output section output low level i sink = 20ma -14.9 -13 -14.9 -13 v i sink = 100ma -14.5 -13 -14.5 -13 output high level i source = 20ma 13 13.5 13 13.5 v i source = 100ma 12 13.5 12 13.5 rise time (note 3) c l = inf, t j = 25c 100 600 100 600 ns fall time (note 3) c l = inf, t j = 25c 100 300 100 300 ns note 3: these parameters, although guaranteed over the recommended operating conditions, are not 100% tested in production. note 4: parameter measured with respect to +v s (pin 6). note 5: parameter measured at +v s (pin 6) with respect to -v s (pin 5). note 6: r t and c t referenced to ground. uc1637 UC2637 uc3637 functional description following is a description of each of the functional blocks shown in the block diagram. oscillator the oscillator consists of two comparators, a charging and discharging current source, a current source set ter- minal, l set and a flip-flop. the upper and lower threshold of the oscillator waveform is set externally by applying a voltage at pins +v th and -v th respectively. the +v th ter- minal voltage is buffered internally and also applied to the l set terminal to develop the capacitor charging current through r t . if r t is referenced to -v s as shown in figure 1, both the threshold voltage and charging current will vary proportionally to the supply differential, and the oscil- lator frequency will remain constant. the triangle wave- form oscillators frequency and voltage amplitude is determined by the external c omponents using the formulas given in figure 1. unless otherwise stated, these specifications apply for t a = -55c to +125c for the uc1637; -25c to +85c for the UC2637; and 0c to +70c for the uc3637: v s = +15v, -v s = - 15v, +v th = 5v, -v th = -5v, r t = 16.7k w , c t = 1500pf, t a =t j. 3
uc1637 UC2637 uc3637 modulation schemes case a zero deadtime (equal voltage on pin 9 and pin 11) in this configuration, maximum holding torque or stiffness and position accuracy is achieved. however, the power in- put into the motor is increased. figure 3a shows this con- figuration. case b small deadtime (voltage on pin 9 > pin 11) a small differential voltage between pin 9 and 11 provides the necessary time delay to reduce the chances of mo- mentary short circuit in the output stage during transi- tions, especially where power-amplifiers are used. refer to figure 3b. case c increased deadtime and deadband mode (voltage on pin 9 > pin 11) with the reduction of stiffness and position accuracy, the power input into the motor around the null point of the servo loop can be reduced or eliminated by widening the window of the comparator circuit to a degree of accep- tance. where position accuracy and mechanical stiffness is unimportant, deadband operation can be used. this is shown in figure 3c. pwm comparators two comparators are provided to perform pulse width modulation for each of the output drivers. inputs are un- committed to allow maximum flexibility. the pulse width of the outputs a and b is a function of the sign and ampli- tude of the error signal. a negative signal at pin 10 and 8 will lengthen the high state of output a and shorten the high state of output b. likewise, a positive error signal re- verses the procedure. typically, the oscillator waveform is compared against the summation of the error signal and the level set on pin 9 and 11. figure 1. oscillator setup figure 2. comparator biasing output drivers each output driver is capable of both sourcing and sinking 100ma steady state and up to 500ma on a pulsed basis for rapid switching of either powerfet or bipolar tran- sistors. output levels are typically -v s + 0.2v @50ma low level and +v s - 2.0v @50ma high level. error amplifier the error amplifier consists of a high slew rate (15v/ m s) op-amp with a typical 1mhz bandwidth and low output im- pedance. depending on the v s supply voltage, the com- mon mode input range and the voltage output swing is within 2v of the v s supply. under-voltage lockout an under-voltage lockout circuit holds the outputs in the low state until a minimum of 4v is reached. at this point, all internal circuitry is functional and the output drivers are enabled. if external circuitry requires a higher starting volt- age, an over-riding voltage can be programmed through the shutdown terminal as shown in figure 4. 4
uc1637 UC2637 uc3637 figure 3. modulation schemes showing (a) zero deadtime (b) deadtime and (c) deadband configurations shutdown comparator the shutdown terminal may be used for implementing various shutdown and protection schemes. by pulling the terminal more than 2.5v below v in , the output drivers will be enabled. this can be realized using an open collector gate or npn transistor biased to either ground or the negative supply. since the threshold is temperature stabi- lized, the comparator can be used as an accurate low voltage lockout (figure 4) and/or delayed start as in fig- ure 5. in the shutdown mode the outputs are held in the low state. current limit a latched current limit amplifier with an internal 200mv offset is provided to allow pulse-by-pulse current limiting. differential inputs will accept common mode signals from -v s to within 3v of the +v s supply while providing excel- lent noise rejection. figure 6 shows a typical current sense circuit. figure 4. external under-voltage lockout figure 5. delayed start-up figure 6. current limit sensing 5
uc1637 UC2637 uc3637 figure 7. bi-directional motor drive with speed control power-amplifier figure 8. single supply position servo motor drive unitrode corporation 7 continental blvd. merrimack, nh 03054 tel. (603) 424-2410 fax (603) 424-3460 6
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