UNITRODE UC1637, UC2637, UC3637 Technical data

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Switched Mode Controller for DC Motor Drive

UC1637
UC2637
UC3637

FEATURES

• 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

BLOCK DIAGRAM

DESCRIPTION

The UC1637 i s a p ul se width modulator circuit intended to be used for a variety of
PWM motor drive and amplifier applications requiring either uni-directional or bi­directiona l drive circuits. When used to replace conventional drivers, this circuit
can increase efficiency and reduce component costs for many applications. All
necessary circuitr y is included to generate an analog error signal and modulate
two bi-direc tional pulse train outpu ts in propor tion to the error signal magnitude
and polarity.

This monolithic device contains a sawtooth oscillator, error amplifier, and two
PWM compar ators 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 -55°C to +125°C, while the UC2637 and UC3637 are characterized for -25°C to
+85°C and 0°C to +70°C, respectively.

ABSOLUTE MAXIMUM RATINGS (Note 1)

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 TA = 25°C (Note 2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1000mW

Power Dissipation at TC = 25°C (Note 2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2000mW

Storage Temperature Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -65°C to +150°C

Lead Temperature (Soldering, 10 Seconds). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +300°C

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.

6/97

CONNECTION DIAGRAM

UC1637
UC2637
UC3637

DIL-18 (TOP VIEW)
J or N Package

SOIC-20 (TOP VIEW)
DW Package

PLCC-20, LCC-20
(TOP VIEW)
Q, L Packages

PACKAGE PIN

FUNCTION

FUNCTION PIN

+V

TH

C

T

-V

TH

A

OUT

-V

S

N/C 6
+V

S

B

OUT

+B

IN

-B

-A
+A

IN
IN

IN

10
11
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

1
2
3
4
5

7
8
9

ELECTRICAL CHARACTERISTICS:

Unless otherwise stated, these specifications apply for TA = -55°C to +125°C for the
UC1637; -25°C to +85°C for the UC2637; and 0°C to +70°C for the UC3637; +VS =
+15V, -VS = - 15V, +V

= 5V, -V

TH

= -5V, RT = 16.7kΩ, CT = 1500pF, TA=T

TH

PARAMETER TEST CONDITIONS UC1637/UC2637 UC3637 UNITS

MIN TYP MAX MIN TYP MAX

Oscillator

Initial Accuracy TJ = 25°C (Note 6) 9.4 10 10.6 9 10 11 kHz
Voltage Stability V

= ±5V to ±20V, V

S

V

= -3V

PIN 3

PIN 1

= 3V,

57 57%

Temperature Stability Over Operating Range (Note 3) 0.5 2 0.5 2 %
+V

Input Bias Current V

TH

Input Bias Current V

-V

TH

+V

-V

TH,

Input Range +VS-2 -VS+2 +VS-2 -VS+2 V

TH

= 6V -10 0.1 10 -10 0.1 10

PIN 2

= 0V -10 -0.5 -10 -0.5

PIN 2

Error Amplifier

Input Offset Voltage VCM = 0V 1.5 5 1.5 10 mV
Input Bias Current V
Input Offset Current V
Common Mode Range V
Open Loop Voltage G ai n R

= 0V 0.5 5 0.5 5

CM

= 0V 0.1 1 0.1 1

CM

= ±2.5 to 20V -VS+2 +VS-VS+2 +V

S

= 10k 75 100 80 100 dB

L

S

Slew Rate 15 15 V/
Unity Gain Bandwidth 2 2 MHz
CMRR Over Common Mode Ra ng e 75 100 75 100 dB
PSRR VS = ±2.5 to ±20V 75 110 75 110 dB

J.

A

µ

A

µ

A

µ

A

µ

V

µ

S

2

UC1637
UC2637
UC3637

ELECTRICAL CHARACTERISTICS:

PARAMETERS TEST CONDITIONS UC1637/UC2637 UC3637 UNITS

Error Amplifier (Continued)

Output Sink Current V
Output Source Current V
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
Input Bias Current V
Input Hysteresis V
Common Mode range V

Current Limit

Input Offset Voltage V
Input Offset Voltage T.C. -0.2 -0.2 mV/°C
Input Bias Current -10 -1.5 -10 -1.5
Common Mode Range 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

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

Output High Level I

Rise Time (Note 3) C
Fall Time (Note 3) C

Note 3: These parameters, although guaranteed over the recommended operating conditions, are not 100% tested in production.
Note 4: Parameter measured with respect to +VS (Pin 6).
Note 5: Parameter meas ure d at +V
Note 6: R

and CT referenced to Ground.

T

PIN 17
PIN 17

= 0V 20 20 mV

CM

= 0V 2 10 2 10

CM

= 0V 10 10 mV

CM

= ±5V to ±20V -VS+1 +VS-2 -VS+1 +VS-2 V

S

= 0V, TJ = 25°C 190 200 210 180 200 220 mV

CM

= ±2.5V to ±20V -V

S

PIN 14

= 20mA -14.9 -13 -14.9 -13 V

SINK

= 100mA -14.5 -13 -14.5 -13

I

SINK
SOURCE

I

SOURCE

(Pin 6) with respect to -VS (Pin 5).

S

Unless otherwise stated, these specifications apply for TA = -55°C to +125°C for the
UC1637; -25°C to +85°C for the UC2637; and 0°C to +70°C for the UC3637: VS =
+15V, -VS = - 15V, +V

= 5V, -VTH = -5V, RT = 16.7kΩ, CT = 1500pF, TA=T

TH

J.

MIN TYP MAX MIN TYP MAX

= 0V -50 -20 -50 -20 mA
= 0V 5 11 5 11 mA

µ

µ

= +VS to -V

S

S

-10 -0.5 -10 -0.5

+VS-3 -V

S

+VS-3 V

µ

= 20mA 13 13.5 13 13.5 V

= 100mA 12 13.5 12 13.5

= Inf, TJ = 25°C 100 600 100 600 ns

L

= Inf, TJ = 25°C 100 300 100 300 ns

L

A

A

A

FUNCTIONAL DESCRIPTION

Following is a descr iption of each of the functional blocks
shown in the Block Diagram.

Oscillator

The oscillator consists of two comparators, a charging
and dischar ging current source, a current sourc e set ter­minal, l
of the oscilla tor waveform is set externally by applying a
voltage at pins +V

and a flip- flop. The upper and lower threshold

SET

and -VTH respectively. The +VTH ter-

TH

minal voltage is buffered internally and also applied to the

terminal to develop the capacitor charging current

l

SET

through R

. If RT is referenced to -VS as shown in Figure

T

1, both the threshold voltage and charging current will
vary proportionally to the supply differential, and the oscil­lator frequency will remain constant. The triangle wave­form oscillators frequency and voltage amplitude is
determ ined by the external components using the formulas
given in Figure 1.

3

UC1637
UC2637
UC3637

Figure 1.

Oscillator Set up

PWM Comparators

Two comparators are provided to perform pulse width
modulation for each of the output drivers. Inputs are un­committed to a llow m ax imum flexibility. The pulse width of
the outputs A and B is a function of the sign and ampli­tude of the er ror signa l. 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 re­verses the procedure. Typically, the oscillator waveform is
compared aga inst the summation of the error signal and
the level set on Pin 9 and 11.

MODULATION SCHEMES

Case A Zero Deadtime

In this con figu rati on, m axi mum ho ld ing t orq ue or stiffness
and position accuracy is achieved. However, the power in­put into the motor is increased. Figure 3A shows this con­figuration.

Case B Small Deadtime

A small diffe renti al v o ltage be twe en Pin 9 and 11 pr ov id es
the necessary time delay to reduce the chances of mo­mentary short circuit in the output stage during transi­tio ns, 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 c an be reduce d or eliminat ed by widening the
window of the comparator circuit to a degree of accep­tance. Where position accuracy and mechanical stiffness
is unimpor tant, de adband operat ion can be used. This is
shown in Figure 3C.

(Equal voltage on Pin 9 and Pin 11)

(Voltage on Pin 9 > Pin 11)

Figure 2.

Comparator Bia si ng

Output Drivers

Each output driver is cap ab le of both sour cing and si nki ng
100mA stea dy state and up to 500mA on a pulsed basis
for rapid switching of either POWERFET or bipolar tran­sistors. Output levels are typically -V
level and +V

- 2.0V @50mA high level.

S

+ 0.2V @50mA low

S

Error Amplifier

The error amplifier consists of a high slew rate (15V/µs)
op-amp with a typical 1MHz bandwidth and low output im­pedance. Depending on the ±V

supply voltage, the com-

S

mon mode input range and the voltage output swing is
within 2V of the V

supply.

S

Under-Voltage Lockout

An under-voltage lockout circuit holds the outputs in the
low state un til a minimum o f 4V is reached. At this point,
all inter n a l cir cu itry is functional and the output drivers are
enabled. If external circuitry requi res a high er starting v olt­age, an over-ridi ng voltage can be programmed through
the shutdown terminal as shown in Figure 4.

4

UC1637
UC2637
UC3637

Figure 3.

Modulation Schemes Showing (A) Zero Dea dt ime (B) Deadti me and (C) Deadban d Con fi gura ti on s

Shutdown Comparator

The shutdown terminal may be used for implementing
various shutdown and prot ection sc hemes. By pulling the
termin al mo re t han 2.5V below V

, the output dr ivers w ill

IN

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 stabi­lized, the comparator can be used as an accurate low
voltage lockout (Figure 4) and/or delayed start as in Fig­ure 5. In the shutdown mode the outputs are held in the
low state.

Figure 5.

-V

S

lent

Delayed Start -Up

to within 3V of the +VS supply while providing excel-

noise rejection. Figure 6 shows a typical current

sense circuit.

Figure 4.

External Under-Voltage Lockout

Current Limit

A latched current limit amplifier with an internal 200mV
offset is p rovided to allow pulse-by-pulse current limiting.
Differential inputs will accept c ommon mode signals from

Figure 6.

5

Current Limit Sensing

UC1637
UC2637
UC3637

Figure 7.

Bi-Directional Motor Drive with Speed Control Power-Amplifier

Figure 8.

UNITRODE CORPORATION
7 CONTINENTAL BLVD. • MERRIMACK, NH 03054
TEL. [phone] • FAX [phone]

Single Supply Position Servo Motor Drive

6

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