Document Outline
- Application Notes
- Design Notes
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
5
7
5
7
%
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
A
-V
TH
Input Bias Current
V
PIN 2
= 0V
-10
-0.5
-10
-0.5
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
A
Input Offset Current
V
CM
= 0V
0.1
1
0.1
1
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/
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
, 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
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
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
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 components 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
, 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/
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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