included
are protective features such as soft-start and under-voltage lockout,
digital current limiting, double pulse inhibit, a data latch for single
pulse metering, adjustable deadtime, and provision for symmetry cor-
rection inputs. For ease of interface, all digital control ports are TTL
and B-series CMOS compatible. Active LOW logic design allows
wired-OR connections for maximum flexibility. This versatile device
can be used to implement single-ended or push-pull switching regu-
lators of either polarity, both transformerless and transformer cou-
pled. The UC1526 is characterized for operation over the full military
temperature range of -55°C to +125°C. The UC2526 is characterized
for operation from -25°C to +85°C, and the UC3526 is characterized
for operation from 0° to +70°C.
Regulating Pulse Width Modulator
FEATURES 8 To 35V Operation 5V Reference Trimmed To
±
1% 1Hz To 400kHz Oscillator Range Dual 100mA Source/Sink Outputs Digital Current Limiting Double Pulse Suppression Programmable Deadtime Under-Voltage Lockout Single Pulse Metering Programmable Soft-Start Wide Current Limit Common Mode Range TTL/CMOS Compatible Logic Ports Symmetry Correction Capability Guaranteed 6 Unit Synchronization
BLOCK DIAGRAM
6/93 ABSOLUTE MAXIMUM RATINGS (Note 1, 2)
Input Voltage (+V
IN
) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +40V
Collector Supply Voltage (+V
C
) . . . . . . . . . . . . . . . . . . . . . +40V
Logic Inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to +5.5V
Analog Inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to +V
IN
Source/Sink Load Current (each output) . . . . . . . . . . . . . 200mA
Reference Load Current . . . . . . . . . . . . . . . . . . . . . . . . . . . 50mA
Logic Sink Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15mA
Power Dissipation at T
A
= +25°C (Note 2) . . . . . . . . . . 1000mW
Power Dissipation at T
C
= +25°C (Note 2) . . . . . . . . . . 3000mW
Operating Junction Temperature . . . . . . . . . . . . . . . . . . +150°C
Storage Temperature Range . . . . . . . . . . . . . . -65°C to +150°C
Lead Temperature (soldering, 10 seconds) . . . . . . . . . . +300°C
Note 1: Values beyond which damage may occur.
Note 2: Consult packaging section of databook for thermal
limitations and considerations of package.
CONNECTION DIAGRAMS
UC1526
UC2526
UC3526
DIL-18, SOIC-18 (TOP VIEW)
J or N Package, DW Package
RECOMMENDED OPERATING CONDITIONS (Note 3)
Input Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +8V to +35V
Collector Supply Voltage . . . . . . . . . . . . . . . . . . . +4.5V to +35V
Sink/Source Load Current (each output) . . . . . . . . . 0 to 100mA
Reference Load Current . . . . . . . . . . . . . . . . . . . . . . 0 to 20mA
Oscillator Frequency Range . . . . . . . . . . . . . . . . 1Hz to 400kHz
Oscillator Timing Resistor . . . . . . . . . . . . . . . . . . . 2k to 150k Oscillator Timing Capacitor . . . . . . . . . . . . . . . . . . . 1nF to 20
µ
F
Available Deadtime Range at 40kHz . . . . . . . . . . . . . 3% to 50%
Operating Ambient Temperature Range
UC1526 . . . . . . . . . . . . . . . . . . . . . . . . . . . . -55°C to +125°C
UC2526 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -25°C to +85°C
UC3526 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0°C to +70°C
Note 3: Range over which the device is functional and
parameter limits are guaranteed.
PACKAGE PIN FUNCTION
FUNCTION
PIN
N/C
1
+Error
2
-Error
3
Comp.
4
C
SS
5
Reset
______
6
- Current Sense
7
+ Current Sense
8
Shutdown
_________
9
R
TIMING
10
C
T
11
R
D
12
Sync
13
Output A
14
V
C
15
N/C
16
Ground
17
Output B
18
+V
IN
19
V
REF
20
PLCC-20, LCC-20
(TOP VIEW)
Q and L Packages
ELECTRICAL CHARACTERISTICS:
PARAMETER
TEST CONDITIONS
UC1526 / UC2526
UC3526
UNITS
MIN
TYP
MAX
MIN
TYP
MAX
Reference Section (Note 4)
Output Voltage
T
J
= + 25°C
4.95
5.00
5.05
4.90
5.00
5.10
V
Line Regulation
+V
IN
= 8 to 35V
10
20
10
30
mV
Load Regulation
I
L
= 0 to 20mA
10
30
10
50
mV
Temperature Stability
Over Operating T
J
15
50
15
50
mV
Total Output
Voltage Range
Over Recommended
Operating Conditions
4.90
5.00
5.10
4.85
5.00
5.15
V
Short Circuit Current
V
REF
= 0V
25
50
100
25
50
100
mA
Under -Voltage Lockout
RESET
_______
Output Voltage
V
REF
= 3.8V
0.2
0.4
0.2
0.4
V
V
REF
= 4.8V
2.4
4.8
2.4
4.8
V
Note 4: I
L
= 0mA.
+V
IN
= 15V, and over operating ambient temperature, unless otherwise
specified, T
A
= T
J.
2 ELECTRICAL CHARACTERISTICS:
PARAMETER
TEST CONDITIONS
UC1526 / UC2526
UC3526
UNITS
MIN
TYP
MAX
MIN
TYP
MAX
Oscillator Section (Note 5)
Initial Accuracy
T
J
= + 25°C
±
3
±
8
±
3
±
8
%
Voltage Stability
+V
IN
= 8 to 35V
0.5
1
0.5
1
%
Temperature Stability
Over Operating T
J
7
10
3
5
%
Minimum Frequency
R
T
= 150k
, C
T
= 20
µ
µ
F
1
1
Hz
Maximum Frequency
R
T
= 2k
, C
T
= 1.0nF
400
400
kHz
Sawtooth Peak Voltage
+V
IN
= 35V
3.0
3.5
3.0
3.5
V
Sawtooth Valley Voltage
+V
IN
= 8V
0.5
1.0
0.5
1.0
V
Error Amplifier Section (Note 6)
Input Offset Voltage
R
S



2k
2
5
2
10
mV
Input Bias Current
-350
-1000
-350
-2000
nA
Input Offset Current
35
100
35
200
nA
DC Open Loop Gain
R
L
10M
64
72
60
72
dB
HIGH Output Voltage
V
PIN1
-V
PIN2



150mV, I
SOURCE
=
100
µ
µ
A
3.6
4.2
3.6
4.2
V
LOW Output Voltage
V
PIN2
-V
PIN1


150mV, I
SINK
=

100
µ
µ
A
0.2
0.4
0.2
0.4
V
Common Mode Rejection
Rs 12k 70
94
70
94
dB
Supply Voltage Rejection
+V
IN
= 12 to 18V
66
80
66
80
dB
PWM Comparator (Note 5)
Minimum Duty Cycle
V
COMPENSATION
= +0.4V
0
0
%
Maximum Duty Cycle
V
COMPENSATION
= +3.6V
45
49
45
49
%
Digital Ports (SYNC, SHUTDOWN, and RESET)
HIGH Output Voltage
I
SOURCE
=40
µ
µ
A
2.4
4.0
2.4
4.0
V
LOW Output Voltage
I
SINK
= 3.6mA
0.2
0.4
0.2
0.4
V
HIGH Input Current
V
IH
= +2.4V
-125
-200
-125
-200
µ
A
LOW Input Current
V
IL
= +0.4V
-225
-360
-225
-360
µ
A
Current LImit Comparator (Note 7)
Sense Voltage
R
S



50
90
100
110
80
100
120
mV
Input Bias Current
-3
-10
-3
-10
µ
A
Soft-Start Section
Error Clamp Voltage
RESET = +0.4V
0.1
0.4
0.1
0.4
V
Cs Charging Current
RESET =+2.4V
50
100
150
50
100
150
µ
A
Output Drivers (Each Output) (Note 8)
HIGH Output Voltage
I
SOURCE
= 20mA
12.5
13.5
12.5
13.5
V
I
SOURCE
= 100mA
12
13
12
13
V
LOW Output Voltage
I
SINK
= 20mA
0.2
0.3
0.2
0.3
V
I
SINK
= 100mA
1.2
2.0
1.2
2.0
V
Collector Leakage
V
C
= 40V
50
150
50
150
µ
A
Rise Time
C
L
= 1000pF
0.3
0.6
0.3
0.6
µ
s
Fall Time
C
L
= 1000pF
0.1
0.2
0.1
0.2
µ
s
Power Consumption (Note 9)
Standby Current
SHUTDOWN
____________

=

+
0.4V
18
30
18
30
mA
+V
IN
= 15V, and over operating ambient temperature, unless otherwise
specified, T
A
= T
J.
UC1526
UC2526
UC3526
Note 4: I
L
= 0mA.
Note 5: F
OSC
= 40kHz (R
T
= 4.12k
±
1%, C
T
= 0.1
µ
F
±
1%,
R
D
= 0 )
Note 6: V
CM
= 0 to +5.2V
Note 8: V
C
= +15V
Note 9: +V
IN
= +35V, R
T
= 4.12k 3 UC1526
UC2526
UC3526
APPLICATIONS INFORMATION
Voltage Reference
T
he reference regulator of the UC1526 is based on a tem-
perature compensated zener diode. The circuitry is fully
active at supply voltages above +8V, and provides up to
20mA of load current to external circuitry at +5.0V. In sys-
tems where additional current is required, an external
PNP transistor can be used to boost the available current.
A rugged low frequency audio-type transistor should be
used, and lead lengths between the PWM and transistor
should be as short as possible to minimize the risk of os-
cillations. Even so, some types of transistors may require
collector-base capacitance for stability. Up to 1 amp of
load current can be obtained with excellent regulation if
the device selected maintains high current gain.
Under-Voltage Lockout
The under-voltage lockout circuit protects the UC1526
and the power devices it controls from inadequate supply
voltage, If +V
IN
is too low, the circuit disables the output
drivers and holds the RESET
_______
pin LOW. This prevents
spurious output pulses while the control circuitry is stabi-
lizing, and holds the soft-start timing capacitor in a dis-
charged state.
The circuit consists of a +1.2V bandgap reference and
comparator circuit which is active when the reference
voltage has risen to 3V
BE
or +1.8V at 25°C. When the ref-
erence voltage rises to approximately +4.4V, the circuit
enables the output drivers and releases the RESET
_______
pin,
allowing a normal soft-start. The comparator has 200mV
of hysteresis to minimize oscillation at the trip point.
When +V
IN
to the PWM is removed and the reference
drops to +4.2V, the under-voltage circuit pulls RESET
_______
LOW again. The soft-start capacitor is immediately dis-
charged, and the PWM is ready for another soft-start cy-
cle.
The UC1526 can operate from a +5V supply by connect-
ing the V
REF
pin to the +V
IN
pin and maintaining the sup-
ply between +4.8 and +5.2V.
Soft-Start Circuit
The soft-start circuit protects the power transistors and
rectifier diodes from high current surges during power
supply turn-on. When supply voltage is first applied to the
UC1526, the under-voltage lockout circuit holds RESET
_______
LOW with Q
3
. Q
1
is turned on, which holds the soft-start
capacitor voltage at zero. The second collector of Q
1
clamps the output of the error amplifier to ground, guaran-
teeing zero duty cycle at the driver outputs. When the
supply voltage reaches normal operating range, RESET
_______
will go HIGH. Q
1
turns off, allowing the internal 100mA
current source to charge C
S
. Q
2
clamps the error ampli-
fier output to 1V
BE
above the voltage on C
S
. As the soft-
start voltage ramps up to +