ST L4976 User Manual

L4976

1A step down switching regulator

Features

■Up to 1A step down converter

■Operating input voltage from 8v to 55v

■Precise 5.1V reference voltage

■Output voltage adjustable from 0.5V to 50V

■Switching frequency adjustable up to 300kHz

■Voltage feedforward

■Zero load current operation

■Internal current limiting (pulse-bypulse

■and hiccup mode)

■Protection against feedback disconnection

■Thermal shutdown

Figure 1. Typical application circuit

DIP8	SO16W

Description

The L4976 is a step down monolithic power switching regulator delivering 1A at a voltage between 3.3V and 50V (selected by a simple external divider). Realized in BCD mixed technology, the device uses an internal power D-

MOS transistor (with a typical Rds(ON) of 0.25Ω) to obtain very high efficency and high switching

speed. A switching frequency up to 300KHz is achievable (the maximum power dissipation of the packages must be observed). A wide input voltage range between 8V to 55V and output voltages regulated from 3.3V to 40V cover the majority of today’s applications. Features of this new generations of DC-DC converter include pulse-by-pulse current limit, hiccup mode for short circuit protection, voltage feedforward regulation, protection against feedback loop disconnection and thermal shutdown. The device is available in plastic dual in line, MINIDIP 8 for standard assembly, and SO16W for SMD assembly.

Vi=8V to 55V

			5			8
		R1
		20K			L4976
			3
						4
C1	C7	C2
			2	7	1	6		L1	VO=3.3V/1A
220 F	220nF	2.7nF						260 H
63V
								(77120)
					R2	C6	D1
						100nF		C8
					9.1K		GI
					C4		SB360	330 F
					22nF

April 2007

Rev 7

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Contents	L4976

Contents

1	Block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		3
2	Pin settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		4
	2.1	Pin connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	4
	2.2	Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	4
3	Electrical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		5

3.1 Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3.2 Thermal data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3.3 Operating temperature rating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

4	Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	. 7
5	Typical charcteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	. 9
6	Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	13
7	Order code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	16
8	Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	17

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L4976	Block diagram

1 Block diagram

Figure 2. Block diagram

VCC

			5
	THERMAL	VOLTAGES
	SHUTDOWN	MONITOR
			CBOOT
2			CHARGE
	VREF	INTERNAL
VREF
		REFERENCE
		5.1V
7			6
COMP
8	E/A	3.3V	BOOT
		PWM
FB
		R
3.3V		Q	CBOOT
		S	CHARGE
		DRIVE	AT LIGHT
	OSCILLATOR		LOADS
	3	1	4
	OSC	GND	OUT

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Pin settings	L4976

2 Pin settings

2.1Pin connection

Figure 3. Pin connection (top view)

			N.C.	1	16	N.C.
GND	1	8	GND	2	15	N.C.
			FB	3	14	FB
VREF	2	7	VREF
			COMP	4	13	COMP
			OSC
OSC	3	6	BOOT	5	12	BOOT
			OUT
OUT	4	5	VCC	6	11	VCC
			OUT
			N.C.	7	10	N.C.
			N.C.	8	9	N.C.
		DIP8			SO16

2.2Pin description

Table 1. Pin description

	N° Pin		Name	Description
DIP8		SO16W (1)
1		2	GND	Ground
2		3	VREF	5.1V Reference voltage with 20mA current capability.
				An external resistor connected between the unregulated
3		4	OSC	input voltage and this pin and a capacitor connected
				from this pin to ground fix the switching frequency. (Line
				feed forward is automatically obtained)
4		5, 6	OUT	Stepdown regulator output.
5		11	VCC	Unregulated DC input voltage.
6		12	BOOT	A capacitor connected between this pin and OUT allows
				to drive the internal VDMOS.
7		13	COMP	E/A output to be used for frequency compensation.
				Stepdown feedback input. Connecting directly to this pin
8		14	FB	results in an output voltage of 3.3V. An external resistive
				divider is required for higher output voltages.

1. Pins 1, 7, 8, 9, 10, 15 and 16 are not internally, electrically connected to the die.

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L4976	Electrical data

3 Electrical data

3.1Maximum ratings

Table 2. Absolute maximum ratings

Symbol			Parameter		Value	Unit
DIP8		S016W
V5		V11	Input voltage		58	V
V4		V5, V6	Output DC voltage		-1	V
			Output peak voltage at t = 0.1µs, f = 200kHz		-5	V
I4		I5, I6	Maximum output current		internal limit
V6-V5		V12-V11			14	V
V6		V12	Bootstrap voltage		70	V
V7		V13	Analogs input voltage (VCC = 24V)		12	V
V8		V14	(VCC = 20V)		6	V
					-0.3	V
	PTOT		Power dissipation a TA ≤ 60°C	DIP8	1	W
				SO16	0.8	W
TJ,TSTG			Junction and storage temperature		-40 to 150	°C

3.2Thermal data

Table 3. Thermal data

Symbol	Parameter	DIP8		S016W		Unit
R	Maximum thermal resistance junction-ambient	90	(1)	110	(1)	°C/W
thJA

1. Package mounted on board

3.3Operating temperature rating

Table 4. Operating temperature rating

Symbol	Parameter	Value	Unit
TJ	Junction temperature range	-40 to 150	°C

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Electrical characteristics	L4976

4 Electrical characteristics

Table 5. Electrical characteristics

(TJ = 25°C, COSC = 2.7nF, ROSC = 20kΩ, VCC = 24V, unless otherwise specified.)

Symbol	Parameter	Test condition		Min	Typ	Max	Unit
Dynamic characteristic
VI	Operating input voltage range	V = 3.3 to 50V; I	= 1A (1)	8		55	V
		O	O
		IO = 0.5A		3.33	3.36	3.39	V
V	Output voltage	IO = 0.2 to 1A		3.292	3.36	3.427	V
O
		VCC = 8 to 55V (1)		3.22	3.36	3.5	V
Vd	Dropout voltage	VCC = 10V; IO = 1A			0.29	0.367	V
		(1)				0.587	V
Il	Maximum limiting current	VCC = 8 to 55V (1)		1.5	2	2.5	A
	Efficiency	VO = 3.3V; IO = 1A			85		%
fs	Switching frequency	(1)		90	100	110	KHz
SVRR	Supply voltage ripple rejection	VI = VCC + 2VRMS; VO = Vref;		60			dB
		IO = 1.A; fripple = 100Hz
	Voltage stability of switching	VCC = 8 to 55V			3	6	%
	frequency
	Temp. stability of switching	TJ = 0 to 125°C			4		%
	frequency
Reference section
	Reference voltage			5.0	5.1	5.2	V
		Iref = 0 to 10mA; (1)		4.950	5.1	5.250	V
		VCC = 8 to 55V
	Line regulation	Iref = 0mA;			5	10	mV
		VCC = 8 to 55V
	Load regulation	Vref = 0 to 5mA;			2	10	mV
		VCC = 0 to 20mA			6	25	mV
	Short circuit current			30	65	100	mA

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