Texas Instruments UC3856J, UC3856DWTR, UC3856DW, UC1856L883B, UC1856L Datasheet

Improved Current Mode PWM Controller

UC1856
UC2856
UC3856

DESCRIPTIONFEATURES

• Pin-for-Pin Compatible With the UC3846

• 65ns Typical Delay From Shutdown to
Outputs, and 50ns Typical Delay From
Sync to Outputs

• Improved Current Sense Amplifier With
Reduced Noise Sensitivity

• Differential Current Sense with 3V
Common Mode Range

• Trimmed Oscillator Discharge Current
for Accurate Deadband Control

• Accurate 1V Shutdown Threshold

• High Current Dual Totem Pole Outputs
(1.5A peak)

• TTL Compatible Oscillator SYNC Pin
Thresholds

• 4kV ESD Protection

The UC3856 is a high performance version of the popular UC3846
series of current mode controllers, and is intended for both design
upgrades and new applications where speed and accuracy are impor­tant. All input to output delays have been minimized, and the current
sense output is slew rate limited to reduce noise sensitivity. Fast 1.5A
peak output stages have been added to allow rapid switching of
power FETs.

A low impedance TTL compatible sync output has been implemented
with a tri-state function when used as a sync input.

Internal chip grounding has been improved to minimize internal
“noise” caused when dr iving large capacitive loads. This, in conjunc­tion with the improved differential current sense amplifier results in
enhanced noise immunity.

Other features include a trimmed oscillator current (8%) for accurate
frequency and dead time control; a 1V, 5% shutdown threshold; and
4kV minimum ESD protection on all pins.

BLOCK DIAGRAM

9/96

UDG-96176

2

UC1856
UC2856
UC3856

ABSOLUTE MAXIMUM RATINGS

Supply V oltage....................................................................+40V

Collector Supply Voltage.....................................................+40V

Output Current, Source or Sink

DC...................................................................................0.5A

Pulse (0.5µs)...................................................................2.0A

Error Amp Inputs....................................................−0.3V to +VIN

Shutdown Input.....................................................−0.3V to +10V

Current Sense Inputs..............................................−0.3V to +3V

SYNC Output Current......................................................±10mA

Error Amplifier Output Current...........................................−5mA

Soft Start Sink Current.......................................................50mA

Oscillator Charging Current .................................................5mA

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

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

Junction Temperature.......................................−55°C to +150°C

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

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

All voltages are with respect to Ground.Currents are positive
into, negative out of the specified terminal.Consult packaging
section of databook for thermal limitations and considerations of
package.

CONNECTION DIAGRAMS

DIL–16,SOIC-16 (Top View)
J or N,DW PACKAGE

PLCC-20 (Top View)
Q PACKAGE

PLCC-28 (Top View)
QP PACKAGE

ELECTRICAL CHARACTERISTICS Unless otherwise stated, these specifications apply for TA = −55°C to +125°C for

UC1856;− 40°C to +85°C for the UC2856;and 0°C to +70°C for the UC3856, VIN

= 15V, RT = 10k, CT = 1nF , TA= TJ.

UC1856/UC2856 UC3856

PARAMETER TEST CONDITIONS MIN TYP MAX MIN TYP MAX UNITS

Reference Section

Output V oltage TJ = 25°C, Io = 1mA 5.05 5.10 5.15 5.00 5.10 5.20 V
Line Regulation VIN = 8V to 40V 20 20 mV
Load Regulation Io =−1mA to −10mA 15 15 mV
Total Output Variation Line, Load, and Temperature 5.00 5.20 4.95 5.25 V
Output Noise Voltage 10Hz < f < 10kHz, TJ = 25°C 50 50 µV
Long T erm Stability TJ = 125°C, 1000 Hrs (Note 2) 5 25 5 25 mV
Short Circuit Current VREF = 0V −25 −45 −65 −25 −45 −65 mA

Oscillator Section

Initial Accuracy TJ = 25°C 180 200 220 180 200 220 kHz

Over Operating Range 170 230 170 230 kHz

3

UC1856
UC2856
UC3856

ELECTRICAL CHARACTERISTICS (cont.)

Unless otherwise stated, these specifications apply for TA = −55°C to

+125°C for UC1856;− 40°C to +85°C for the UC2856;and 0°C to +70°C for the UC3856, VIN

= 15V, RT = 10k, CT = 1nF , TA= TJ.

UC1856/UC2856 UC3856

PARAMETER TEST CONDITIONS MIN TYP MAX MIN TYP MAX UNITS

Oscillator Section (cont.)

Voltage Stability VIN = 8V to 40V 2 2 %
Discharge Current TJ = 25°C, VCT = 2V 7.5 8.0 8.8 7.5 8.0 8.8 mA

VCT = 2V 6.7 8.0 8.8 6.7 8.0 8.8 mA
Sync Output High Level Io =−1mA 2.4 3.6 2.4 3.6 V
Sync Output Low Level Io =+1mA 0.2 0.4 0.2 0.4 V

Sync Input High Level CT = 0V, RT = VREF 2.0 1.5 2.0 1.5 V
Sync Input Low Level CT = 0V, RT =VREF 1.5 0.8 1.5 0.8 V

Sync Input Current CT = 0V, RT = VREF 1 10 1 10 µA

VSYNC = 5V
Sync Delay to Outputs CT = 0V, RT =VREF 50 100 50 100 ns

VSYNC = 0.8V to 2V

Error Amplifier Section

Input Offset Voltage VCM = 2V 5 10 mV
Input Bias Current −1 −1 µA
Input Offset Current 500 500 nA
Common Mode Range VIN = 8V to 40V 0 VIN − 2 0 VIN − 2V
Open Loop Gain Vo = 1.2V to 3V 80 100 80 100 dB
Unity Gain Bandwidth TJ = 25°C 1 1.5 1 1.5 MHz
CMRR VCM = 0V to 38V, VIN = 40V 75 100 75 100 dB
PSRR VIN = 8V to 40V 80 100 80 100 dB
Output Sink Current VID =−15mV, VcOMP = 1.2V 5 10 5 10 mA
Output Source Current VID = 15mV, VCOMP = 2.5V −0.4 −0.5 −0.4 −0.5 mA
Output High Level VID = 50mV, RL (COMP) = 15k 4.3 4.6 4.9 4.3 4.6 4.9 V
Output Low Level VID =−50mV, RL (COMP) = 15k 0.7 1 0.7 1 V

Current Sense Amplifier Section

Amplifier Gain VCS−=0V, CL SS Open (Notes 3,4) 2.5 2.75 3.0 2.5 2.75 3.0 V/V
Maximum Differential CL SSOpen (Note 3) 1.1 1.2 1.1 1.2 V
Input Signal (VCS+− Vcs-) RL (COMP) = 15k
Input Offset Voltage V

CL SS = 0.5V 5 35 5 35 mV

COMP Open (Note 3)
CMRR VCM = 0V to 3V 60 60 dB
PSRR VIN = 8V to 40V 60 60 dB
Input Bias Current VCL SS = 0.5V, COMP Open (Note 3) −1 −3 −1 −3 µA
Input Offset Current VCL SS = 0.5V, COMP Open (Note 3) 1 1 mA
Input Common Mode Range 0 3 0 3 V
Delay to Outputs V

EA+ = VREF, EA−=0V 120 250 120 250 ns

CS+ − CS−=0V to 1.5V

Current Limit Adjust Section

Current Limit Offset V

CS- = 0V 0.43 0.5 0.57 0.43 0.5 0.57 V

VCS+ = 0V, COMP = Open (Note 3)
Input Bias Current VEA+ =VREF, VEA−=0V −10 −30 −10 −30 µA

Shutdown Terminal Section

Threshold V oltage 0.95 1.00 1.05 0.95 1.00 1.05 V
Input V oltage Range 0 5 0 5 V