FAN5631 データシートの表示（PDF） - Fairchild Semiconductor

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FAN5631

Regulated Step-Down Charge Pump DC/DC Converter

Fairchild Semiconductor 

Switch Configuration

VIN

S1

C+

S2

C

B

VOUT

S3

C-

S4

C

OUT

VIN

S1

C+

S2

VOUT

C

B

S3

C-

S4

C

OUT

GND

2:1 configuration

Switches in charging phase

Reverse all switches for pumping phase

Figure 15. 2:1 Configuration

GND

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

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 1μA. 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)

In the FAN5632, VSEL can be tied to ground to enable

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

2.9V to 3.5V. For normal operation, tie VSEL high.

© 2006 Fairchild Semiconductor Corporation

FAN5631/FAN5632 Rev. 1.0.2

9

www.fairchildsemi.com

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