ST L6928 User Manual

L6928

High efficiency monolithic synchronous step down regulator

Features

■2 V to 5.5 V battery input range

■High efficiency: up to 95%

■Internal synchronous switch

■No external Schottky required

■Extremely low quiescent current

■1 µA max shutdown supply current

■800 mA max output current

■Adjustable output voltage from 0.6 V

■Low dropout operation: up to 100% duty cycle

■Selectable low noise/low consumption mode at light load

■Power Good signal

■± 1% output voltage accuracy

■Current-mode control

■1.4 MHz switching frequency

■Externally synchronizable from 1 MHz to 2 MHz

■OVP

■Short-circuit protection

Applications

■Battery-powered equipment

■Portable instruments

■Cellular phones

■PDAs and hand held terminals

Figure 1. Application test circuit

MSOP8

VFQFPN8 (3x3x1.0 mm)

■DSC

■GPS

Description

The device is DC-DC monolithic regulator specifically designed to provide extremely high efficiency. L6928 supply voltage can be as low as 2 V allowing its use in single Li-Ion cell supplied applications. Output voltage can be selected by an external divider down to 0.6 V. Duty cycle can saturate to 100% allowing low dropout operation. The device is based on a 1.4 MHz fixed frequency, current mode architecture. Low consumption mode operation can be selected at light load conditions, allowing switching losses to be reduced. L6928 is externally synchronizable with a clock which makes it useful in noise sensitive applications. Other features like Power Good, overvoltage protection, short-circuit protection and thermal shutdown (150 °C) are also present.

					5	LX L 4.7 µH			VIN = 1.8 V
VIN= 2 to 5.5 V	VCC
			6				R3		C2
	RUN							R2
							500k
C1			1		8	PGOOD			10µF
								200k
	SYNC								6.3V
10µF			7		3
6.3V						VFB
								R1
				2	4			100k
		COMP		C3	GND
				220pF
			R1
			10k						AM10473v1

December 2011 Doc ID 11051 Rev 7 1/16

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Contents	L6928

Contents

1	Pin settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		3
2	Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		4
3	Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		5
4	Operation description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		7
	4.1	Modes of operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	7

4.1.1 Low consumption mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 4.1.2 Low noise mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 4.1.3 Synchronization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

	4.2	Short circuit protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	. 8
	4.3	Slope compensation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	9
	4.4	Loop stability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	9
5	Additional features and protections . . . . . . . . . . . . . . . . . . . . . . . . . . .		10

5.1 DROPOUT operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 5.2 PGOOD (Power Good output) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 5.3 Adjustable output voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 5.4 OVP (Overvoltage protection) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 5.5 Thermal shutdown . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

6	Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	11
7	Order codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	14
8	Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	15

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L6928	Pin settings

1 Pin settings

Figure 2. Pin connection (top view)

	RUN	1	8	PGOOD	RUN	1	8	PGOOD
	COMP	2	7	SYNC	COMP	2	7	SYNC
	VFB	3	6	VCC			E-pad
					VFB	3	6	VCC
	GND	4	5	LX
		D01IN1239AMOD			GND	4	5	LX
							AM10471v1

	Table 1.	Pin description
	Pin n°	Name	Description
	1	RUN	Shutdown input. When connected to a low level (lower than 0.4 V) the device
			stops working. When high (higher than 1.3 V) the device is enabled.
	2	COMP	Error amplifier output. A compensation network has to be connected to this pin.
			Usually a 220 pF capacitor is enough to guarantee the loop stability.
	3	VFB	Error amplifier inverting input. The output voltage can be adjusted from 0.6 V up
			to the input voltage by connecting this pin to an external resistor divider.
	4	GND	Ground.
	5	LX	Switch output node. This pin is internally connected to the drain of the internal
			switches.
			Input voltage. The start up input voltage is 2.2 V (typ) while the operating input
	6	VCC	voltage range is from 2 V to 5.5 V. An internal UVLO circuit realizes a 100 mV
			(typ.) hysteresis.
			Operating mode selector input. When high (higher than 1.3 V) the low
			consumption mode is selected. When low (lower than 0.5 V) the low noise mode
	7	SYNC	is selected. If connected with an appropriate external synchronization signal
			(from 500 kHz up to 1.4 MHz) the internal synchronization circuit is activated
			and the device works at the same switching frequency.
			Power good comparator output. It is an open drain output. A pull-up resistor
	8	PGOOD	should be connected between PGOOD and VOUT (or VCC depending on the
			requirements). The pin is forced low when the output voltage is lower than 90%
			of the regulated output voltage and goes high when the output voltage is greater
			than 90% of the regulated output voltage. If not used the pin can be left floating.
	-	E-Pad	To be connected to GND plane for optimal thermal performance.

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Maximum ratings	L6928

2 Maximum ratings

Table 2.	Absolute maximum ratings
Symbol		Parameter	Value	Unit
V6		Input voltage	-0.3 to 6	V
V5		Output switching voltage	-1 to VCC	V
V1		Shutdown	-0.3 to VCC	V
V3		Feedback voltage	-0.3 to VCC	V
V2		Error amplifier output voltage	-0.3 to VCC	V
V8		PGOOD	-0.3 to VCC	V
V7		Synchronization mode selector	-0.3 to VCC	V
PTOT		Power dissipation at TA = 70 °C	0.45	W
TJ		Junction operating temperature range	-40 to 150	°C
TSTG		Storage temperature range	-65 to 150	°C
LX pin		Maximum withstanding voltage range test condition:	±1000	V
		CDF-AEC-Q100-002- “Human body model”
Other pins			±2000	V
		acceptance criteria: “normal performance’

	Table 3.	Thermal data
	Symbol	Parameter	Value	Unit
	RthJA	Maximum thermal resistance junction-ambient for MSOP8	180	°C/W
		Maximum thermal resistance junction-ambient for VFQFPN8	56	°C/W

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L6928	Electrical characteristics

3 Electrical characteristics

TJ = 25 °C, VIN = 3.6 V unless otherwise specified.

Table 4.		.
		Electrical characteristics (1)
Symbol		Parameter		Test condition		Min.	Typ.	Max.	Unit
Vcc		Operating input voltage	After turn on		(1)	2		5.5	V
Vcc ON		Turn On threshold					2.2		V
Vcc OFF		Turn Off threshold						2	V
Vcc hys		Hysteresis					100		mV
Rp		High side RON	Vcc	= 3.6 V, Ilx =100 mA			240	300	mΩ
					(1)			400
Rn		Low side RON	Vcc	= 3.6 V, Ilx =100 mA			215	300	mΩ
					(1)			400
		Peak current limit	Vcc	= 3.6 V		1	1.2	1.5	A
Ilim					(1)	0.85		1.65
		Valley current limit	Vcc	= 3.6 V		1	1.4	1.7	A
					(1)	0.9		1.85
VOUT		Output voltage range				Vfb		VCC	V
fosc		Oscillator frequency					1.4		MHz
fsync		Sync mode clock (2)				1		2	MHz
DC characteristics
		Quiescent current (low	Vsync = 0 V, no load,				230		µA
		noise mode)	VFB > 0.6 V
Iq
		Quiescent current (low	Vsync = VCC, no load,		(1)		25	50	µA
		consumption mode)	VFB > 0.6 V
Ish		Shutdown current	RUN to GND, VCC = 5.5 V				0.2		µA
			RUN to GND, VLX = 5.5 V,				1		µA
Ilx		LX leakage current (2)	VCC = 5.5 V
			RUN to GND, VLX = 0 V,				1		µA
			VCC = 5.5 V
Error amplifier characteristics
Vfb		Voltage feedback				0.593	0.600	0.607	V
					(1)	0.590	0.600	0.610	V
I	fb	Feedback input current (2)	V	= 0.6 V			25		nA
			FB
Run
Vrun_H		RUN threshold high						1.3	V
Vrun_L		RUN threshold low				0.4			V

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