TEXAS INSTRUMENTS UC1856, UC2856, UC3856 Technical data

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UC1856 UC2856 UC3856

Improved Current Mode PWM Controller

FEATURES

DESCRIPTION

•Pin-for-Pin Compatible With the UC3846 The UC3856 is a high performance version of the popular 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

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 driving 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

UDG-96176

9/96

ABSOLUTE MAXIMUM RATINGS

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

		UC1856/UC2856				UC3856
PARAMETER	TEST CONDITIONS	MIN	TYP	MAX	MIN	TYP	MAX	UNITS
Reference Section
Output Voltage	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 Term 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

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, V CT = 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 − 2	V
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 SS Open (Note 3)	1.1	1.2		1.1	1.2		V
Input Signal (VCS+ − Vcs-)	RL (COMP) = 15k

Input Offset Voltage	VCL 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	VEA+ = VREF, EA− = 0V		120	250		120	250	ns
	CS+ − CS− = 0V to 1.5V
Current Limit Adjust Section
Current Limit Offset	VCS- = 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 Voltage		0.95	1.00	1.05	0.95	1.00	1.05	V

Input Voltage Range		0		5	0		5	V

VCS+

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.

UC1856

UC2856

UC3856

		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 Voltage		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 VEA+ = VREF, VEA- = 0V.
Note 4:	Amplifier gain defined as:	VCOMP
	G =			VCS− = 0V to 1.0V
			;

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