ST L6920DB User Manual

General features

■ 0.8V start up input voltage

■ Up to 5.5V operating input voltage

■ Internal synchronous rectifier

■ Adjustable output voltage from 1.8V

■ 3.3V and 5V fixed output voltages

■ Low battery voltage detection

■ Reverse battery protection

■ 750mA 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

L6920DB

Synchronous rectifier step up converter

MSOP8

Description

The L6920DB 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.

Application circuit

L6920DB

October 2006 Rev 5 1/16

3.3V

www.st.com

16

Contents L6920DB

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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L6920DB Pin settings

1 Pin settings

1.1 Pin connection

Figure 1. Pin connection (top view)

1.2 Pin 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.

3LBO

4 REF 1.23V reference voltage. Bypass this output to GND with a 100nF

5 SHDN

6 GND Ground pin

7 LX Step-up inductor connection

8 OUT Power OUTPUT pin

Battery low voltage detector output. If the voltage at the LBI pin drops
below the internal threshold typ. 1.23V, LBO goes low.

The LBO is an open drain output and so a pull-up resistor (about
200KΩ) has to be added for correct output setting .

capacitor for filtering high frequency noise. No capacitor is required for
stability

Shutdown pin. When pin 5 is below 0.2V the device is in shutdown,
when pin 5 is above 0.6V the device is operating.

3/16

Electrical data L6920DB

2 Electrical data

2.1 Maximum ratings

Table 2. Absolute maximum ratings

Symbol Parameter Value Unit

V

ccmax

Vcc to GND 6 V

LBI, SHDN

, FB to GND 6 V

V

out max

Vout to GND 6 V

2.2 Thermal data

Table 3. Thermal data

Symbol Parameter Value Unit

R

thJA

T

Maximum thermal resistance junction-ambient 180 ° C/W

Maximum junction temperature 150 °C

J

4/16

L6920DB Electrical characteristics

3 Electrical characteristics

Table 4. Electrical characteristcs

(V

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

IN

Symbol Parameter Test condition Min Typ Max Unit

V

Section

CC

V

Minimum Start Up Input

IN

Voltage

I

Quiescent Current

q

= 3.3V

V

out

= 0 mA, FB = 1.4V, V

I

l

LBI = SHDN = 2V

Il = 0 mA, FB = 1.4V, V
LBI = SHDN = 2V

= 3.3V

out

out

= 5V

0.8 V

912µA

11 15 µA

I

Shut Down Current

sd

Irev Reverse battery current

Power section

R

R

Active switch ON resistance 300 mΩ

on-N

Synchronous switch ON

on-P

resistance

Control section

V

ou

t

Output voltage

Output voltage range External divider 1.8 5.2 V

V

V

T

onmax

T

offmin

SHDN

LBI threshold

LBI

LBO logic LOW

LBO

I

LX switch current limit

lim

Maximum on time

Minimum off time

SHDN logic LOW 0.2 V

= 5V, Il = 0 mA

V

V

in

= -4V

in

0.1 1 µA

0.1 1 µA

300 mΩ

FB = OUT, I

FB = GND, I

= 0 mA 3.2 3.3 3.4

l

= 0 mA 4.955.1

l

1.23

= 1mA 0.2 0.4

I

sink

0.7 0.8 0.9

V

= 3.3V 3.75 5 6.25

out

= 3.3V 0.75 1 1.25

V

out

V

V

V

V

A

µs

µs

SHDN logic HIGH 0.6 V

V

Reference Voltage

ref

1.18 1.23 1.27

V

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