FAN5665 Fairchild Semiconductor, FAN5665 Datasheet - Page 11

• Manufacturer Part Number: FAN5665
• Description: The FAN5665 is a 5V switched capacitor step-up DC/DC converter with an input voltage range from 2
• Manufacturer: Fairchild Semiconductor

© 2007 Fairchild Semiconductor Corporation
FAN5665 • Rev. 1.0.1
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.
Figure 39. Block Diagram
11
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
V
shutdown if die temperature exceeds 150°C.
OUT
>150mV, protection is in the form of thermal
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