ST L4973 User Manual

L4973

3.5 A step down switching regulator

Features

■Up to 3.5 A step down converter

■Operating input voltage from 8 V to 55 V

■3.3 V and 5.1 V (±1%) fixed output, and adjustable outputs from:

–0.5 V to 50 V (3.3 type)

–5.1 V to 50 V (5.1 type)

■Frequency adjustable up to 300 kHz

■Voltage feed forward

■Zero load current operation (min. 1 mA)

■Internal current limiting (pulse by pulse and HICCUP mode)

■Precise 5.1 V (1.5%) reference voltage externally available

■Input/output synchronization function

■Inhibit for zero current consumption (100 mA typ. at VCC = 24 V)

■Protection against feedback disconnection

■Thermal shutdown

■Output over voltage protection

■Soft-start function

Figure 1. Internal schematic diagram

DIP-18 (12+3+3)	SO-20 (12+4+4)

Description

The L4973 is a step down monolithic power switching regulator delivering 3.5 A at fixed voltages of 3.3 V or 5.1 V and using a simple external divider output adjustable voltage up to 50V. Realized in BCD mixed technology, the device uses an internal power D-MOS transistor

(with a typical RDS(on) of 0.15 Ω) to obtain very high efficiency and very fast switching times.

Switching frequency up to 300 kHz are achievable (the maximum power dissipation of the packages must be observed).

A wide input voltage range between 8 V to 55 V and output voltages regulated from 3.3 V to 40 V cover the majority of the today applications.

Features of this new generation of DC-DC converter includes pulse by pulse current limit, hiccup mode for output short circuit protection, voltage feed forward regulation, soft-start, input/output synchronization, protection against feedback loop disconnection, inhibit for zero current consumption and thermal shutdown. Packages available are in plastic dual in line, DIP18 (12+3+3) for standard assembly, and SO20 (12+4+4) for SMD assembly.

VCC (8V to 55V)		7	8			12	CBOOT
	ROSC						9
		1		L4973			3	VO(3.3V or 5.1V)
CIN	C2	4,5,6,10					L1
		13,14,15		16	17	11	2
							RCOMP
		COSC				CSS	D1	COUT
							CCOMP
					D97IN554A
February 2009			Rev 18					1/28
								www.st.com

Contents	L4973

Contents

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

3.1 Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3.2 Thermal data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

4	Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	. 6
5	Evaluation board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	. 9
6	Application circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	12
7	Typical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	13
8	Application ideas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	21
9	Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	23
10	Order code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	26
11	Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	27

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L4973	Block diagram

1 Block diagram

Figure 2. Block diagram

	INH			V5.1			VCC	VCC
10(11)				16(18)		7(8)		8(9)
									CBOOT
									CHARGE
ZERO CURRENT		VREF		INTERNAL		INTERNAL	5.1V
	INHIBIT	GOOD	5.1V			SUPPLY
			3.3V	REFERENCE
17(19)		SOFT		HICCUP CURRENT
SS
		START		LIMITING
11(12)
COMP
		THERMAL		CURRENT
		SHUTDOWN		LIMITING
5.1V				R	Q				BOOT
3.3V	+	-							9(10)
VFB	E/A			S	Q
	-	PWM
12(13)		+
SYNC	OSCILLATOR
18(20)							DRIVER
			4,5,6,13,14,15
		1(1)	(4,5,6,7,14,15,16,17)				2(2)	3(3)
	OSC			GND			OUT	OUT	D94IN161B
Pin x = Powerdip
Pin (x) = S020

2 Pin settings

2.1Pin connection

Figure 3. Pin connection (top view)

OSC	1	18	OSC	1	20	SYNC
			SYNC	2	19	SS
OUT	2	17	OUT
			SS	3	18	V5.1
OUT	3	16	OUT
			V5.1	4	17	GND
GND	4	15	GND
			GND	5	16	GND
GND	5	14	GND
			GND	6		GND
GND	6	13	GND		15
			GND	7		GND
VCC			GND		14
	7	12	VFB	8		VFB
VCC	8	11	VCC		13
			COMP	9
BOOT	9	10	VCC		12	COMP
			INH
		D94IN162A	BOOT	10	11	INH
					D94IN163A
	DIP -18 (12+3+3)			SO20 (12+4+4)

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Pin settings	L4973

2.2Pin description

Table 1.	Pin description
	N° Pin			Name	Description
DIP-18		SO-20
11		12		COMP	E/A output to be used for frequency compensation
					A logic signal (active high) disables the device (sleep
10		11		INH	mode operation). If not used it must be connected to
					GND; if floating the device is disabled.
9		10		BOOT	A capacitor connected between this pin and the output
					allows to drive the internal D-MOS.
18		20		SYNC	Input/Output synchronization.
7,8		8,9		VCC	Unregulated DC input voltage
2,3		2,3		OUT	Stepdown regulator output.
					Stepdown feedback input. Connecting the output
					directly to this pin results in an output voltage of 3.3 V
					for the L4973V3.3 and 5.1 V for L4973V5.1. An external
12		13		VFB	resistive divider is required for higher output voltages.
					For output voltage resistive divider is required for higher
					output voltages. For output voltage less than 3.3 V, see
					Note: 1 and Figure 33.
16		18		V5.1	Reference voltage externally available.
4,5,6		4,5,6,7		GND	Signal ground
13,14,15		14,15,16,17
					An external resistor connected between the unregulated
1		1		OSC	input voltage and Pin 1 and a capacitor connected from
					Pin 1 to ground fixes the switching frequency. (Line feed
					forward is automatically obtained)

Note: 1 The maximum power dissipation of the package must be observed.

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L4973	Electrical data

3 Electrical data

3.1Maximum ratings

Table 2.		Absolute maximum ratings
Symbol			Parameter	Value	Unit
DIP-18		S0-20
V7,V8		V9,V8	Input voltage	58	V
V2,V3		V2,V3	Output DC voltage	-1	V
			Output peak voltage at t = 0.1 μs f = 200 kHz	- 5	V
I2,I3		I2,I3	Maximum output current	int. limit.
V9-V8		V10-V8		14	V
V9		V10	Bootstrap voltage	70	V
V11		V12	Analogs input voltage (VCC = 24 V)	12	V
V17		V19	Analogs input voltage (VCC = 24 V)	13	V
V12		V13	(VCC = 20 V)	6	V
				-0.3	V
V18		V20	(VCC = 20 V)	5.5	V
				0.3	V
V10		V11	Inhibit	VCC	V
				-0.3	V
			DIP 12+3+3
			Power dissipation a Tpins ≤ 90 °C	5	W
Ptot			(TA = 70 °C no copper area)	1.3	W
			(TA = 70 °C 4 cm copper area on PCB)	2	W
			SO-20
			Power dissipation a Tpins = 90 °C	4	W
TJ,TSTG			Junction and storage temperature	-40 to 150	°C

3.2Thermal data

Table 3.	Thermal data
Symbol		Parameter	DIP-18	SO-20	Unit
RthJP		Maximum thermal resistance junction-pin	12	15	°C/W
R		Maximum thermal resistance junction-ambient	60 (1)	80 (1)	°C/W
thJA

1. Package mounted on board

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Electrical characteristics	L4973

4 Electrical characteristics

Table 4.	Electrical characteristics
	(Refer to the test circuit,VCC = 24 V; TJ = 25 °C, COSC = 2.7 nF;
	ROSC = 20 kΩ; unless otherwise specified)
Symbol	Parameter				Test condition				Min	Typ	Max	Unit
Dynamic characteristics
	Input voltage range (1)	V	O	= V	REF	to 40 V; I	= 3.5A	(2)	8		55	V
							O
	Output voltage	IO = 1 A							5.05	5.1	5.15	V
		IO = 0.5 A to 3.5 A VCC = 8 V							5.00	5.1	5.20	V
	L4973V5.1
		to 55 V						(2)	4.95	5.1	5.25	V
	Output voltage	IO = 1 A							3.326	3.36	3.393	V
		IO = 0.5 A to 3.5 A VCC = 8 V							3.292	3.36	3.427	V
	L4973V3.3
		to 40 V						(2)	3.26	3.36	3.46	V
	RDS(on )	VCC = 10.5 V IO = 3.5 A								0.15	0.22	Ω
								(2)			0.35	Ω
	Maximum limiting	VCC = 8 V to 55 V						(2)	3.8	4.5	5.5	A
	current								4	4.5	5.5	A
η	Efficiency	VO = 5.1 V; IO = 3.5 A								90		%
		VO = 3.3 V; IO = 3.5 A								85		%
	Switching frequency							(2)	90	100	110	kHz
	Supply voltage ripple	Vi = VCC+2 VRMS VO = Vref;							60			dB
	rejection	IO = 1 A; fripple = 100 Hz
	Switching frequency
fsw	stability vs., supply	VCC = 8 V to 55 V								2	5	%
	voltage
Reference section
	Reference voltage	Iref = 0 to 20 mA;							5.025	5.1	5.175	V
		VCC = 8 to 55 V						(2)	4.950	5.1	5.250	V
	Line regulation	Iref = 0 mA;								5	10	mV
		VCC = 8 to 55 V
	Load regulation	Vref = 0 to 5 mA;								2	10	mV
		VCC = 0 to 20 mA								6	25	mV
	Short circuit current								30	65	100	mA

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L4973						Electrical characteristics
	Table 4.		Electrical characteristics (continued)
			(Refer to the test circuit,VCC = 24 V; TJ = 25 °C, COSC = 2.7 nF;
			ROSC = 20 kΩ; unless otherwise specified)
	Symbol		Parameter	Test condition		Min	Typ		Max	Unit
	Soft-start
			Soft-start charge current			30	45		60	μA
			Soft-start discharge			15	22		30	μA
			current
	Inhibit
			High level voltage		(2)	3.0				V
			Low level voltage		(2)				0.8	V
			Isource high level	VINH = 3 V	(2)	10	16		50	μA
			Isource low level	VINH = 0.8 V	(2)	10	15		50	μA
	DC characteristics
			Total operating	Duty cycle = 50 %			4		6	mA
			quiescent current
			Quiescent current	Duty cycle = 0			2.7		4	mA
			Total stand-by quiescent	VCC = 24 V; VINH = 5 V			100		200	μA
			current	VCC = 55 V; VINH = 5 V			150		300	μA
	Error amplifier
			High level output voltage			11.0				V
			Low level output voltage						0.65	V
			Source bias current			1	2		3	μA
			Source output current			200	300		600	μA
			Sink output current			200	300			μA
			Supply voltage ripple	VCOMP = VFB		60	80			dB
				CREF = 4.7 μF 1-5 mA load
			rejection
				current
			DC open loop gain	RL = ∞		50	60			dB
			Transconductance	Icomp = -0.1 to 0.1 mA;			2.5			mS
				Vcomp = 6 V
	Oscillator section
			Ramp valley			0.78	0.85		0.92	V
			Ramp peak	VCC = 8 V		1.9	2.1		2.3	V
				VCC = 55 V		9	9.6		10.2	V
			Maximum duty cycle			95	97			%

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Electrical characteristics								L4973
	Table 4.	Electrical characteristics (continued)
		(Refer to the test circuit,VCC = 24 V; TJ = 25 °C, COSC = 2.7 nF;
		ROSC = 20 kΩ; unless otherwise specified)
	Symbol	Parameter	Test condition	Min	Typ		Max	Unit
		Maximum frequency	Duty cycle = 0%;				300	kHz
			ROSC =13 kΩ; COSC = 820 pF;
	Sync function
		High input voltage	VCC = 8 V to 55 V	3.5				V
		Low input voltage	VCC = 8 V to 55 V				0.9	V
		Slave sink current		0.15	0.25		0.45	mA
		Master output amplitude	Isource = 3 mA	4	4.5			V
		Output pulse width	No load, Vsync = 4.5 V	0.20	0.35			μs

1.Pulse testing with a low duty cycle

2.Specifications referred to TJ from -40 °C to 125 °C.

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L4973	Evaluation board

5 Evaluation board

Figure 4. Evaluation board circuit

SYNCH

R6 NM

JP1

Vin

3

1

2

C8

220n

U1

7 8

10

18

9

R1

VCC

VCC

INH

SYNC

BOOT

OUT 3

15k

2

1

OSC

OUT

R7

NM

17

SS

15

GND

Q2

14

C6

GND

16

13

NM

C10

V5.1

GND

NM

6

C9

GND

470u 63v

COMP

5

GND

220n

VFB

4

GND

L4973 DIP 18

signal GND

11

12

C4

22n

C1

C2

C3

C3A

R5

C5

2.7n

470n

NM

1u

GND

NM

R2

150p

15k

signal GND

GND plane

1 2

L1	68uH				Vout
				R3
		C7	C11	2.7k	C14
D1				C12
		NM	150u 50v	150u 50v C13	NM
STPS5L60
				NM
					R4
					4.99k

GND

Table 5.	Component list (fsw = 150 kHz, VOUT = 5 V)
Reference		Description	Part number	Manufacturer
R1		Resistor 15 kΩ 1%
R2		Resistor 15 kΩ 1%
R3		Resistor 2.7 kΩ 1%
R4		Resistor 4.99 kΩ 1%
R5		Not mounted
R6		Not mounted
R7		Not mounted
C1		Capacitor 2.7 nF 5%
C2		Capacitor 470 nF 5%
C3		Capacitor 1 μF 5%
C4		Capacitor 22 nF 5%
C5		Capacitor 150 pF 5%
C6		Not mounted
C7		Not mounted
C8		Capacitor 220 nF 5%
C9		Capacitor 220 nF 5%
C10		Capacitor 470 μF 63V	EKY-630ELL471ML20S	Nippon Chemi-con

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