Datasheet

ELECTRICAL CHARACTERISTICS:
PARAMETER TEST CONDITIONS UC1851 / UC2851 UC3851 UNITS
MIN TYP MAX MIN TYP MAX
Ramp Generator
Ramp Current, Minimum
I
SENSE = −10µA
-11 -14 -11 -14 µA
Ramp Current, Maximum I
SENSE = 1.0mA -0.9 -.95 -0.9 -.95 mA
Ramp Valley 0.3 0.4 0.6 0.3 0.4 0.6 V
Ramp Peak Clamping Level 3.9 4.2 4.5 3.9 4.2 4.5 V
Error Amplifier
Input Offset Voltage V
CM = 5.0V 0.5 5 2 10 mV
Input Bias Current 0.5 2 1 5 µA
Input Offset Current 0.5 0.5 µA
Open Loop Gain
∆V
O = 1 to 3V
60 66 60 66 dB
Output Swing (Max Output ≤
Ramp Peak - 100mV)
Minimum Total Range 0.3 3.5 0.3 3.5 V
CMRR V
CM = 1.5 to 5.5V 70 80 70 80 dB
PSRR V
IN = 8 to 30V 70 80 70 80 dB
Short Circuit Current V
COMP = 0V -4 -10 -4 -10 mA
Gain Bandwidth (Note 1) T
J = 25°C, AVOL = 0dB 1 2 1 2 MHz
Slew Rate (Note 1) T
J = 25°C, AVCL = 0dB 0.8 0.8 V/µs
PWM Section
Continuous Duty Cycle Range
(other than zero) (Note 1)
Minimum Total Continuous Range
Ramp Peak < 4.2V
246246%
Output High Level I
SOURCE = 20mA 18 18.5 18 18.5 V
I
SOURCE = 200mA 17 18.5 17 18.5 V
Rise Time (Note 1) T
J = 25°C, CL = 1nF 50 150 50 150 ns
Fall Time (Note 1) T
J = 25°C, CL = 1nF 50 150 50 150 ns
Output Saturation I
OUT = 20mA 0.2 0.4 0.2 0.4 V
I
OUT = 200mA 1.7 2.2 1.7 2.2 V
Comparator Delay (Note 1)
Pin 8 to Pin 12, T
J = 25°C, RL = 1kΩ
300 500 300 500 ns
Sequencing Functions
Comparator Thresholds Pins 2, 3, 5 2.8 3.0 3.2 2.8 3.0 3.2 V
Input Bias Current Pins 3, 5 = 0V -1.0 -4.0 -1.0 -4.0 µA
Input Leakage Pins 3, 5 = 10V 0.1 2.0 0.1 2.0 µA
Start/UV Hysteresis Current Pin 2 = 2.5V 170 200 220 170 200 230 µA
Ext. Stop Threshold Pin 4 0.8 1.6 2.4 0.8 1.6 2.4 V
Error Latch Activate Current Pin 4 = 0V, Pin 3 > 3V -120 -200 -120 -200 µA
Driver Bias Saturation Voltage,
V
IN-VOH
IB = -50mA 2 3 2 3 V
Driver Bias Leakage V
B = 0V -0.1 -10 -0.1 -10 µA
Slow-Start Saturation I
S = 10mA 0.2 0.5 0.2 0.5 V
Slow-Start Leakage V
S = 4.5V 0.1 2.0 0.1 2.0 µA
Current Control
Current Limit Offset 0 5 0 10 mV
Current Shutdown Offset 370 400 430 360 400 440 mV
Input Bias Current Pin 7 = 0V -2 -5 -2 -5 µA
Common Mode Range (Note 1) -0.4 3.0 -0.4 3.0 V
Current Limit Delay (Note 1) T
J = 25°C, Pin 7 to 12, RL = 1k 200 400 200 400 ns
Note 1:Guaranteed by design. Not 100% tested in production.
UC1851
UC2851
UC3851
Unless otherwise stated, these specifications apply for TA = -55°C to +125°C for the
UC1851, -40°C to +85°C for the UC2851, and 0°C to 70°C for the UC3851; VIN =
20V, RT = 20kΩ, CT = .001 mfd, RR = 10kΩ, CR = .001mfd. Current Limit Threshold
= 200mV, TA = TJ.
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