Texas Instruments UC3573N, UC3573DTR, UC3573D, UC2573J, UC2573N Datasheet

UC1573

UC2573

UC3573

Buck Pulse Width Modulator Stepdown Voltage Regulator

FEATURES

∙Simple Single Inductor Buck PWM Stepdown Voltage Regulation

∙Drives External PMOS Switch

∙Contains UVLO Circuit

∙Includes Pulse-by-Pulse Current Limit

∙Low 50μA Sleep Mode Current

DESCRIPTION

The UC3573 is a Buck pulse width modulator which steps down and regulates a positive input voltage. The chip is optimized for use in a single inductor buck switching converter employing an external PMOS switch. The block diagram consists of a precision reference, an error amplifier configured for voltage mode operation, an oscillator, a PWM comparator with latching logic, and a 0.5A peak gate driver. The UC3573 includes an undervoltage lockout circuit to insure sufficient input supply voltage is present before any switching activity can occur, and a pulse-by-pulse current limit. Input current can be sensed and limited to a user determined maximum value. In addition, a sleep comparator interfaces to the UVLO circuit which turns the chip off when the input voltage is below the UVLO threshold. This reduces the supply current to only 50μA, making the UC3573 ideal for battery powered applications.

BLOCK DIAGRAM

UDG-94106-1

SLUS346 - APRIL 1999

ABSOLUTE MAXIMUM RATINGS

VCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35V EAINV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . –0.6V to VCC

IEAOUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25mA RAMP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . –0.3V to 4V

CS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . –0.3V to VCC

IOUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . –0.7A to 0.7A I3VREF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . –15mA Storage Temperature . . . . . . . . . . . . . . . . . . . –65°C to +150°C

Junction Temperature. . . . . . . . . . . . . . . . . . . –65°C to +150°C Lead Temperature (Soldering, 10 sec.) . . . . . . . . . . . . . +300°C

Currents are positive into, negative out of the specified terminal. Consult Packaging Section of Databook for thermal limitations and considerations of packages.

UC1573

UC2573

UC3573

CONNECTION DIAGRAMS

DIL-8, SOIC-8 (TOP VIEW)

J or N, D Packages

ELECTRICAL CHARACTERISTICS: Unless otherwise specified, these parameters apply for TA = –55°C to +125°C for the UC1573, –40°C to +85°C for the UC2573, and 0°C to +70°C for the UC3573, VCC = 5V, CT = 680pF, T A = TJ.

PARAMETER	TEST CONDITIONS	MIN	TYP	MAX	UNITS
Reference Section
3VREF		2.94	3	3.06	V
Line Regulation	VCC = 4.75 to 30V		1	10	mV
Load Regulation	I3VREF = 0 to –5mA		1	10	mV
Oscillator Section
Frequency	VCC = 5V, 30V	85	100	115	kHz
Error Amp Section
EAINV	EAOUT = 2V	1.45	1.5	1.55	V
IEAINV	EAOUT = 2V		–0.2	–1	μA
AVOL	EAOUT = 0.5V to 3V	65	90		dB
EAOUT High	EAINV = 1.4V	3.6	4	4.4	V
EAOUT Low	EAINV = 1.6V		0.1	0.2	V
IEAOUT	EAINV = 1.4V, EAOUT = 2V	–350	–500		μA
	EAINV = 1.6V, EAOUT = 2V	7	20		mA
Unity Gain Bandwidth	TJ = 25°C, F = 10kHz	0.6	1		MHz
Current Sense Comparator Section
Threshold (referred to VCC)		–0.39	–0.43	–0.47	V
Input Bias Current	CS = VCC		150	800	nA
CS Propagation Delay			400		ns
Gate Drive Output Section
OUT High Saturation	IOUT = 0		0	0.3	V
	IOUT = –10mA		0.7	1.5	V
	IOUT = –100mA		1.5	2.5	V
OUT Low Saturation	IOUT = 10mA		0.1	0.4	V
	IOUT = 100mA		1.5	2.2	V
Rise Time	TJ = 25°C, C LOAD = 1nF + 3.3 Ohms		30	80	ns
Fall Time	TJ = 25°C, C LOAD = 1nF + 3.3 Ohms		30	80	ns
Pulse Width Modulator Section
Maximum Duty Cycle	EAINV = 1.4V		92	96	%
Minimum Duty Cycle	EAINV = 1.6V			0	%
Modulator Gain	EAOUT = 1.5V to 2.5V	25	35	45	%/V
Undervoltage Lockout Section
Start Threshold		3.5	4.2	4.5	V
Hysteresis		100	200	300	mV

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