© 2006 Fairchild Semiconductor Corporation

www.fairchildsemi.com

FAN5631/FAN5632 Rev. 1.0.2

9

Switch Configuration

S1

S2

S3

S4

V

IN

GND

C+

V

OUT

C-

C

OUT

2:1 configuration

Switches in charging phase

Reverse all switches for pumping phase

C

B

S1

S3

S4

V

IN

GND

C+

VOUT

C-

C

OUT

1:1 configuration

Switch 3 is always off

Switch 4 is always on

Switches 1 and 2 are in phase 1

Reverse position of switches 1&2 for phase 2

C

B

S2

Figure 15.

2:1 Configuration

Figure 16.

1:1 Configuration

Shutdown, UVLO, Short-Circuit,

Current-Limit and Thermal Shutdown

The device has an active-low shutdown pin to decrease

supply current to less than 1

μA. In shutdown mode, the

supply is disconnected from the output. UVLO triggers

when supply voltage drops below 2V. When the output

voltage is lower than 150mV, a short-circuit protection is

triggered. In this mode, 15 out of 16 pulses during the

switching are skipped and the supply current is limited.

Thermal shutdown triggers at 150ºC.

Efficiency Optimizer (FAN5632)

the

efficiency

optimizer

feature.

To

achieve

an

optimized efficiency, the switch mode configuration

transition point is shifted from a 2:1 to a 1:1 mode until

the output voltage falls to 20% of its nominal value. For

example, when the nominal output voltage is 1.5V, the

output voltage is allowed to drop to 1.2V. This maintains

a peak efficiency of 85% for the input voltage range of