© 2007 Fairchild Semiconductor Corporation

www.fairchildsemi.com

FAN5665 • Rev. 1.0.0

11

Block Diagram

Figure 39. Block Diagram

Functional Description

Overview

FAN5665 is a 5V switched capacitor regulator with very

low output ripple and high efficiency. The maximum

output current is 30mA.

Linear Regulation Loop

The linear regulation loop (consisting of the power

transistors, output feedback, and error amplifier), is

used to regulate the output voltage and reduce current

spikes at mode change.

Soft-start

At power-up, the device has 0.5ms soft-start to control

the inrush current and make the output ramp up slowly.

Modes of Operation

FAN5665 has 1×, 1.5×, and 2× modes. Input voltage is

compared with reference to determine mode.

Light / Heavy Load Monitor

In 1.5× / 2× mode, there is a current sense to detect the

output current. If a light-load condition is detected, the

device switches to a lower switching frequency around

50kHz. This frequency is a good compromise between

achieving high light-load efficiency and not causing

audible noise generation. If the load is heavy (typically

more than 5mA), the device switches at 1.2MHz to

decrease the output voltage ripple.

Protection

FAN5665 has thermal shutdown protection when the

die temperature is more than 150°C. It turns back off

when the temperature falls by about 10°C.

Short-circuit protection helps avoid damage to the

device when the output is shorted to ground. Whenever

output voltage is pulled below 150mV, short-circuit

protection is triggered and limits the input current. If

shutdown if die temperature exceeds 150°C.