design features 2.7V to 38V VIN Range, Low Noise, 250mA Buck-Boost
Charge Pump Converter
George H. Barbehenn The LTC3245 is a buck-boost regulator that dispenses with the traditional inductor,
and instead uses a capacitor charge pump. The LTC3245’s input voltage range is
2.7V to 38V, and it can be used without a feedback divider to produce one of two
fixed output voltages, 3.3V and 5V, or programmed via a feedback divider to any
output voltage from 2.5V to 5.5V. Maximum output current is 250mA. As a result of
its buck-boost topology, the LTC3245 is capable of regulating a voltage above or
below the input voltage, allowing it to satisfy automobile cold crank requirements.
The LTC3245 achieves efficiency of
80% when delivering 5V, 100m A from
a 12V source, significantly higher efficiency than an LDO, making it possible
to avoid the space and cost requirements of an LDO with a heat sink. The
LTC3245 is available in an exposed
pad MSOP12 or 3mm Г— 4mm DFN12. Because N and M are integers, a straight
charge pump cannot be used to produce an arbitrary output. Instead the
controller modifies VIN to produce VIN′,
which is then fed to the charge pump.
The charge pump can operate in one of
three modes, buck, LDO or boost, resulting in ½VIN′, VIN′ or 2VIN′, respectively. CHARGE PUMP OPERATION By properly controlling both VIN′ and
the operating mode of the charge pump
any arbitrary voltage can be achieved.
When operating in buck mode, the …