ST L6902D User Manual

L6902D

L6902D

UP TO 1A SWITCHING REGULATOR WITH

ADJUSTABLE CURRENT LIMIT

■UP TO 1A OUTPUT CURRENT

■OPERATING INPUT VOLTAGE FROM 8V TO 36V

■PRECISE 3.3V (±2%) REFERENCE VOLTAGE

■5% OUTPUT CURRENT ACCURACY

■OUTPUT VOLTAGE ADJUSTABLE FROM 1.235V TO 34V

■250KHz INTERNALLY FIXED FREQUENCY

■VOLTAGE FEEDFORWARD

■ZERO LOAD CURRENT OPERATION

■ADJUSTABLE CURRENT LIMIT

■PROTECTION AGAINST FEEDBACK DISCONNECTION

■THERMAL SHUTDOWN

APPLICATIONS

■CHARGERS FOR NiCd, NiMH BATTERIES AND PREREGULATOR FOR LITHIUM-ION BATTERIES

■ADJUSTABLE CURRENT GENERATOR

■SIMPLE STEP-DOWN CONVERTERS WITH ADJUSTABLE CURRENT LIMIT

■BATTERY EQUIPPED SYSTEMS

■DISTRIBUTED POWER SUPPLY

■MOBILE PC & SUBNOTEBOOK

DESCRIPTION

The L6902D is a complete and simple step down switching regulator with adjustable current limit. Based on a voltage mode structure it integrates a cur-

TEST AND APPLICATION CIRCUIT

SO8

ORDERING NUMBERS: L6902D

L6902D013TR (Tape & Reel)

rent error amplifier to have a constant voltage and constant current control.

By means of an on board current sense resistor and the availability of the current sense pins (both compatible to Vcc and for Cscompatible with GND too) a current limit programming is very simple and accurate (±5%). Moreover constant current control can be used to charge NiMH and NiCd batteries.

The device can be used as a standard DC/DC converter with adjustable current limit (set by using the external sense resistor).

The internal robust P-Channel DMOS transistor with a typical of 250mΩ assures high efficiency and a minimum dropout even at high output current level. The internal limiting current (latched function) of typical value of 2.5A protects the device from accidental output short circuit avoiding dangerous loads damage.

If the temperature of the chip goes higher than a fixed internal threshold (150°C with 20°C hysteresis), the power stage is turned off.

VIN=8V to 36V			VCC	8	OUT	L1 22µH	RSENSE	VOUT=3.3V
			VREF		1		100mΩ
		3.3V		6		D1
						STPS340U	R1
			COMP		2
				4			5.6K
C1					3			C4
		C2
10µF					FB			100µF
25V	C3	22nF		7	5			10V
CERAMIC	220pF	R3		GND			R2	POSCAP
		5.1K					3.3K
	D01IN1306A

June 2002

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L6902D

DESCRIPTION (Continued)

Other protections beside thermal shutdown complete the device for a safe and reliable application: overvoltage protection, frequency folback overcurrent protection and protection vs. feedback disconnection.

The internal fixed switching frequency of 250KHz, and the SO-8 package pin allow to built an ultra compact DC/ DC converter with a minimum board space.

PIN CONNECTION

O U T		1	8		V C C
C S +		2	7		G N D
C S -		3	6		V R E F
C O M P		4	5		F B

PIN DESCRIPTION

N°	Pin								Function
1	OUT	Regular Output
2	CS+	Current Error Amplifier input (current sense at higher voltage)
3	CS-	Current Error Amplifier input (current sense at lower voltage)
4	COMP	E/A output to be used for frequency compensation
5	FB	Stepdown feedback input. Connecting directly to this pin results in an output voltage of 1.235V.
		An external resistive divider is required for higher output voltages. In this case:
		V		= V		× æ1	R1	æ1	R1
			out		FB		+ -------ö = 1.235V		+ -------ö
						è	R2ø	è	R2ø
6	VREF	3.3V VREF. No cap is need for stability.
7	GND	Ground
8	VCC	Unregulated DC input voltage.

THERMAL DATA

Symbol	Parameter	Value	Unit
Rth j-amb	Thermal Resistance Junction to Ambient Max.	110 (*)	°C/W

(*) Package mounted on board.

ABSOLUTE MAXIMUM RATINGS

Symbol	Parameter	Value	Unit
V8	Input Voltage	40	V
V1	Output DC voltageOutput peak voltage at t = 0.1ms	-1 to 40	V
		-5 to 40	V
I1	Maximum output current	Internally limited
V4, V5	Analog pins	4	V
V2, V3	Analog pins	-0.3V to VCC	V
Ptot	Power dissipation at Tamb £ 70 °C	0.7	W
Tj	Operating junction temperature range	-40 to 150	°C
Tstg	Storage temperature range	-55 to 150	°C

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