ST L5973AD User Manual

L5973AD

2 A switch step down switching regulator

Features

■2 A internal switch

■Operating input voltage from 4 V to 36 V

■3.3 V / (±2%) reference voltage

■Output voltage adjustable from 1.235 V to 35 V

■Low dropout operation: 100% duty cycle

■500 kHz Internally fixed frequency

■Voltage feedforward

■Zero load current operation

■Internal current limiting

■Inhibit for zero current consumption

■Synchronization

■Protection against feedback disconnection

■Thermal shutdown

Applications

■Consumer: STB, DVD, TV, VCR, car radio, LCD monitors

■Networking: XDSL, modems, DC-DC modules

■Computer: printers, audio/graphic cards, optical storage, hard disk drive

■Industrial: chargers, car battery, DC-DC converters

Figure 1. Test application circuit

HSOP8 exposed pad

Description

The L5973AD is a step down monolithic power switching regulator with a switch current limit of 2 A so it is able to deliver more than 1.5 A DC current to the load depending on the application conditions.

The output voltage can be set from 1.235 V

to 35 V. The high current level is also achieved thanks to an SO8 package with exposed frame,

that allows to reduce the RthJA down to approximately 40 °C/W.

The device uses an internal P-Channel D-MOS transistor (with a typical of 200 mΩ) as switching element to avoid the use of bootstrap capacitor and guarantee high efficiency.

An internal oscillator fixes the switching frequency at 500 kHz to minimize the size of external components.

Having a minimum input voltage of 4 V only, it is particularly suitable for 5 V bus, available in all computer related applications.

Pulse by pulse current limit with the internal frequency modulation offers an effective constant current short circuit protection.

	3.3V	VREF			OUT	L1 15μH		VOUT=3.3V
		6
VIN = 4V to 35V		VCC			1
						D1
		8	L5973AD				R1
	SYNC. 2					STPS340U
							5.6K	C2
					5
C1		COMP	3	7				330μF
	C4	4			FB			10V
10μF
			INH		GND
35V	22nF						R2
CERAMIC	C3	R3					3.3K
	220pF	4.7K
					D03IN1453
November 2009			Doc ID 9552 Rev 9					1/22
								www.st.com

Contents	L5973AD

Contents

1	Pin settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		3
	1.1	Pin connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	3
	1.2	Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	3
2	Electrical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		4

2.1 Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.2 Thermal data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

3	Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		. 5
4	Functional description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		. 7
	4.1	Power supply and voltage reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	8
	4.2	Voltages monitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	8
	4.3	Oscillator and synchronization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	8
	4.4	Current protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	9
	4.5	Error amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	10
	4.6	PWM comparator and power stage . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	11
	4.7	Inhibit function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	12
	4.8	Thermal shutdown . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	12
5	Additional features and protections . . . . . . . . . . . . . . . . . . . . . . . . . . .		13

5.1 Feedback disconnection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 5.2 Output overvoltage protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 5.3 Zero load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 5.4 Application circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

6	Application ideas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	16
7	Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	18
8	Order code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	20
9	Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	21

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L5973AD	Pin settings

1 Pin settings

1.1Pin connection

Figure 2. Pin connection (top view)

1.2Pin description

	Table 1.	Pin description
	N°	Type	Description
	1	OUT	Regulator output.
			Master/slave synchronization. When it is open, a signal synchronous with the
			turn-off of the internal power is present at the pin. When connected to an
	2	SYNC	external signal at a frequency higher than the internal one, then the device is
			synchronized by the external signal.
			Connecting together the SYNC pin of two devices, the one with the higher
			frequency works as master and the other one, works as slave.
			A logical signal (active high) disables the device. With IHN higher than 2.2 V
	3	INH	the device is OFF and with INH lower than 0.8V, the device is ON.
			If INH is not used the pin must be grounded. When it is open, an internal pull-
			up disables the device.
	4	COMP	E/A output to be used for frequency compensation.
			Stepdown feedback input. Connecting the output voltage directly to this pin
	5	FB	results in an output voltage of 1.235 V. An external resistor divider is required
			for higher output voltages (the typical value for the resistor connected
			between this pin and ground is 4.7 K).
	6	VREF	Reference voltage of 3.3 V. No filter capacitor is needed to stability.
	7	GND	Ground.
	8	VCC	Unregulated DC input voltage.

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Electrical data	L5973AD

2 Electrical data

2.1Maximum ratings

Table 2.	Absolute maximum ratings
Symbol		Parameter	Value	Unit
V8		Input voltage	40	V
V1		Output DC voltage	-1 to 40	V
		Output peak voltage at t = 0.1 μs	-5 to 40	V
I1		Maximum output current	int. limit.
V4, V5		Analog pins	4	V
V3		INH	-0.3V to VCC
V2		SYNC	-0.3 to 4	V
PTOT		Power dissipation at TA ≤ 60 °C	2.25	W
TJ		Operating junction temperature range	-40 to 150	°C
TSTG		Storage temperature range	-55 to 150	°C

2.2Thermal data

	Table 3.	Thermal data
	Symbol	Parameter	HSOP8	Unit
			Exposed pad
	RthJA	Maximum thermal resistance junction-ambient	40 (1)	°C/W

1. Package mounted on board

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L5973AD	Electrical characteristics

3 Electrical characteristics

TJ = 25 °C, VCC = 12 V, unless otherwise specified
Table 4.		Electrical characteristics
Symbol			Parameter	Test condition			Min	Typ	Max	Unit
V	CC		Operating input voltage	V = 1.235 V; I	o	= 2 A	4		36	V
			range	o
RDS(on)			MOSFET on					0.250	0.5	Ω
			resistance
	Il		Maximum limiting	VCC = 4.4 V to 36 V			2	2.3	3.5	A
			current
fs			Switching frequency					500		kHz
			Duty cycle				0		100	%
Dynamic characteristics (see test circuit).
V5			Voltage feedback	4.4 V < VCC < 36 V,			1.220	1.235	1.25	V
				20 mA < IO < 2 A
η			Efficiency	VO = 5 V, VCC = 12 V				90		%
DC characteristics
Iqop			Total operating					5	7	mA
			quiescent current
Iq			Quiescent current	Duty cycle = 0;					2.7	mA
				VFB = 1.5 V
Iqst-by			Total stand-by	Vinh > 2.2 V				50	100	μA
			quiescent current
Inhibit
			INH threshold voltage	Device ON					0.8	V
				Device OFF			2.2			V
Error amplifier
VOH			High level output	VFB = 1 V			3.5			V
			voltage
VOL			Low level output	VFB = 1.5 V					0.4	V
			voltage
Io source			Source output current	VCOMP = 1.9 V;			200	300		μA
				VFB = 1 V
Io sink			Sink output current	VCOMP = 1.9 V;			1	1.5		mA
				VFB = 1.5 V
Ib			Source bias current					2.5	4	μA
			DC open loop gain	RL = ∞			50	57		dB

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Electrical characteristics								L5973AD
	Table 4.	Electrical characteristics (continued)
	Symbol		Parameter	Test condition		Min	Typ	Max	Unit
				Icomp = -0.1 mA to
	gm		Transconductance	0.1mA			2.3		mS
				VCOMP = 1.9 V
	Sync function
			High input voltage	VCC = 4.4 V to 36 V		2.5		VREF	V
			Low input voltage	VCC = 4.4 V to 36 V				0.74	V
			Slave sink current	Vsync = 0.74 V	(1)	0.11		0.25	mA
						0.21		0.45	mA
				Vsync = 2.33 V
			Master output	Isource = 3 mA		2.75	3		V
			amplitude
			Output pulse width	no load, Vsync = 1.65 V		0.20	0.35		μs
	Reference section
			Reference voltage			3.234	3.3	3.366	V
				IREF = 0 to 5 mA		3.2	3.3	3.399	V
				VCC = 4.4 V to 36 V
			Line regulation	IREF = 0 mA			5	10	mV
				VCC = 4.4 V to 36 V
			Load regulation	IREF = 0 to 5 mA			8	15	mV
			Short circuit current			10	18	30	mA

1. Guaranteed by design.

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L5973AD	Functional description

4 Functional description

The main internal blocks are shown in Figure 3, where is reported the device block diagram. They are:

●A voltage regulator that supplies the internal circuitry. From this regulator, a 3.3 V reference voltage is externally available.

●A voltage monitor circuit that checks the input and internal voltages.

●A fully integrated sawtooth oscillator whose frequency is 500 kHz

●Two embedded current limitations circuitries which control the current that flows through the power switch. The Pulse by Pulse Current Limit forces the power switch OFF cycle by cycle if the current reaches an internal threshold, while the Frequency Shifter reduces the switching frequency in order to strongly reduce the duty cycle.

●A transconductance error amplifier.

●A pulse width modulator (PWM) comparator and the relative logic circuitry necessary to drive the internal power.

●An high side driver for the internal P-MOS switch.

●An inhibit block for stand-by operation.

●A circuit to realize the thermal protection function.

Figure 3. Block diagram

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