Improved Current Mode PWM Controller
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
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.
UC1856
UC2856
UC3856
• 4kV ESD Protection
BLOCK DIAGRAM
9/96
UDG-96176
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.
UC1856
UC2856
UC3856
CONNECTION DIAGRAMS
DIL–16,SOIC-16 (Top View)
J or N,DW PACKAGE
PLCC-28 (Top View)
QP PACKAGE
PLCC-20 (Top View)
Q 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
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
= 15V, RT = 10k, CT = 1nF , TA= TJ.
UC1856/UC2856 UC3856
2
UC1856
UC2856
UC3856
ELECTRICAL CHARACTERISTICS (cont.)
+125°C for UC1856;− 40°C to +85°C for the UC2856;and 0°C to +70°C for the UC3856, VIN
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
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
Current Limit Adjust Section
Current Limit Offset V
Input Bias Current VEA+ =VREF, VEA−=0V −10 −30 −10 −30 µA
Shutdown T erminal 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
CL SS = 0.5V 5 35 5 35 mV
COMP Open (Note 3)
EA+ = VREF, EA−=0V 120 250 120 250 ns
CS+ − CS−=0V to 1.5V
CS- = 0V 0.43 0.5 0.57 0.43 0.5 0.57 V
VCS+ = 0V, COMP = Open (Note 3)
Unless otherwise stated, these specifications apply for TA = −55°C to
= 15V, RT = 10k, CT = 1nF , TA= TJ.
UC1856/UC2856 UC3856
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
UC1856/UC2856 UC3856
PARAMETER TEST CONDITIONS MIN TYP MAX MIN TYP MAX UNITS
Shutdown Terminal Section (cont.)
Minimum Latching (Note 5) 3 1.5 3 1.5 mA
Current (ICL SS)
Maximum Non-Latching (Note 6) 1.5 0.8 1.5 0.8 mA
Current (ICL SS)
Delay to Outputs VSHUTDOWN = 0 to 1.3V 65 110 65 110 ns
Output Section
Collector-Emitter V oltage 40 40 V
Off-State Bias Current VC = 40V 250 250 µA
Output Low Level IOUT = 20mA 0.1 0.5 0.1 0.5 V
IOUT = 200mA 0.5 2.6 0.5 2.6 V
Output High Level IOUT =−20mA 12.5 13.2 12.5 13.2 V
IOUT =−200mA 12 13.1 12 13.1 V
Rise Time C1 = 1nF 40 80 40 80 ns
Fall Time C1 = 1nF 40 80 40 80 ns
UVLO Low Saturation VIN = 0V, IOUT = 20mA 0.8 1.5 0.8 1.5 V
PWM Section
Maximum Duty Cycle 45 47 50 45 47 50 %
Minimum Duty Cycle 0 0 %
Undervoltage Lockout Section
Startup Threshold 7.7 8.0 7.7 8.0 V
Threshold Hysterisis 0.7 0.7 V
Total Standby Current
Supply Current 18 23 18 23 mA
Note 1: All voltages are with respect to GND.Currents are positive into, negative out of the specified terminal.
Note 2: This parameter, although guaranteed over the recommended operating conditions is not 100% tested in production.
Note 3: Parameter measured at trip point of latch with V
Note 4: Amplifier gain defined as:
G
∆
V
COMP
=
∆
VCS+
;
+ =VREF, V
EA
-=
0V.
∆
V
CS
−=
0V to 1.0V
EA
Note 5: Current into CL SS guaranteed to latch circuit into shutdown state.
Note 6: Current into CL SS guaranteed not to latch circuit into shutdown state.
= 15V, RT = 10k, CT = 1nF , TA= TJ.
4