ST L6920DC User Manual

L6920DC

Synchronous rectifier step up converter

General features

■0.8V start up input voltage

■Up to 5.5V operating input voltage

■Internal synchronous rectifier

■Adjustable output voltage from 1.8V to 5.5V

■3.3V and 5V fixed output voltages

■Low battery voltage detection

■Reverse battery protection

■550mA minimum input current limit

■Switching frequency up to 1MHz

■1.23V reference voltage available

Applications

■Conversion from 1 to 3 alkaline,

■NiMH, NiCd battery cells or 1 lithium ION

■PDA and handheld instruments

■Digital cameras

■Cellular phones

■GPS

■Distributed power

MSOP8

Description

The L6920DC is a high efficiency monolithic step up switching converter IC especially designed for battery powered application.

Package is MSOP8 in order to minimize PCB space. It requires only three external components to realize the conversion from the battery voltage to the selected output voltage.

The minimum output voltage is 1.8V: suitable to supply the most advanced ASIC and µP.

High switching frequency allows for a low profile, small sized inductor and output capacitor to be used.

Reference voltage, low battery detection and Shutdown are provided together with over current, over voltage.

Application circuit

L6920DC	3.3V

June 2006

Rev 1

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Contents	L6920DC

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	Typical performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		. 6
5	Detailed description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		7
	5.1	Principle of operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	7
	5.2	Start-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	9
	5.3	Shutdown . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	10
	5.4	Low battery detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	10
	5.5	Low battery input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	10
	5.6	Reverse polarity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	10
	5.7	Output voltage selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	10
6	Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		12
7	Order code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		14
8	Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		15

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L6920DC	Pin settings

1 Pin settings

1.1Pin connection

Figure 1. Pin connection (top view)

1.2Pin description

Table 1. Pin description

N°		Type						Description
1			FB			Output voltage selector. Connect FB to GND for Vout=5V or to OUT for
						Vout=3.3V. Connect FB to an external resistor divider for adjustable
						output voltage
2			LBI			Battery low voltage detector input. The internal threshold is set to 1.23V.
						A resistor divider is needed to adjust the desired low battery threshold.
3						Battery low voltage detector output. If the voltage at the LBI pin drops
			LBO
						below the internal threshold typ. 1.23V,			LBO	goes low.
						The		is an open drain output and so a pull-up resistor (about
							LBO
						200KΩ) has to be added for correct output setting .
4			REF			1.23V reference voltage. Bypass this output to GND with a 100nF
						capacitor for filtering high frequency noise. No capacitor is required for
						stability
5						Shutdown pin. When pin 5 is below 0.2V the device is in shutdown,
		SHDN
						when pin 5 is above 0.6V the device is operating.
6		GND				Ground pin
7			LX			Step-up inductor connection
8		OUT				Power OUTPUT pin

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Electrical data	L6920DC

2 Electrical data

2.1Maximum ratings

Table 2. Absolute maximum ratings

Symbol			Parameter	Value	Unit
Vccmax	Vcc to GND			6	V
	LBI,		FB to GND	6	V
		SHDN,
Vout max	Vout to GND			6	V

2.2Thermal data

Table 3. Thermal data

Symbol	Parameter	Value	Unit
RthJA	Maximum thermal resistance junction-ambient	180	° C/W
TJ	Maximum junction temperature	150	° C

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L6920DC	Electrical characteristics

3 Electrical characteristics

Table 4. Electrical characteristcs

(VIN = 2V, FB = GND, TJ = 25°C unless otherwise specified)

Symbol					Parameter	Test condition	Min	Typ	Max	Unit
VCC Section
	VIN			Minimum Start Up Input		Vout = 3.3V		0.8		V
				Voltage
						Il = 0 mA, FB = 1.4V, Vout = 3.3V		9	12	µA
						LBI = SHDN = 2V
	Iq			Quiescent Current
						Il = 0 mA, FB = 1.4V, Vout = 5V		11	15	µA
						LBI = SHDN = 2V
	Isd			Shut Down Current		Vin = 5V, Il = 0 mA		0.1	1	µA
	Irev			Reverse battery current		Vin = -4V		0.1	1	µA
Power section
	Ron-N			Active switch ON resistance				300		mΩ
	Ron-P			Synchronous switch ON				300		mΩ
				resistance
Control section
	Vout			Output voltage		FB = OUT, Il = 0 mA	3.2	3.3	3.4	V
						FB = GND, Il = 0 mA	4.9	5	5.1	V
				Output voltage range		External divider	1.8		5.5	V
	VLBI			LBI threshold				1.23		V
	VLBO			LBO logic LOW		Isink = 1mA		0.2	0.4	V
	Ilim			LX switch current limit			0.55		0.9	A
Tonmax				Maximum on time		Vout = 3.3V	3.75	5	6.25	µs
	Toffmin			Minimum off time		Vout = 3.3V	0.75	1	1.25	µs
					logic LOW				0.2	V
	SHDN
				SHDN
					logic HIGH		0.6			V
				SHDN
	Vref			Reference Voltage			1.18	1.23	1.27	V

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