Datasheet

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
µ
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
= 25°C 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
µ
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
µ
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
= 25°C 100 600 100 600 ns
Fall Time (Note 3) C
L
= Inf, T
J
= 25°C 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
= -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: V
S
=
+15V, -V
S
= - 15V, +V
TH
= 5V, -V
TH
= -5V, R
T
= 16.7k
, C
T
= 1500pF, T
A
=T
J.
3