4

LTC1516

COMP1

COMP2

COMP3

CLOCK 1

CLOCK 2

CONTROL

LOGIC

S3

S2A

S2B

S2C

S1A

S1B

S1C

S1D

0.22

µF

10

µF

0.22

µF

10

µF

SHDN

LTC1516 • BD

CHARGE PUMP SHOWN IN TRIPLER MODE, DISCHARGE CYCLE

CHARGE PUMP

+

+

Operation

The LTC1516 uses a switched capacitor charge pump to

voltage. Regulation is achieved by sensing the output

voltage through an internal resistor divider and enabling

the charge pump when the output voltage droops below

the lower trip point of COMP2. When the charge pump is

enabled, a 2-phase, nonoverlapping clock controls the

charge pump switches. Clock 1 closes the S1 switches

which enable the flying capacitors, C1 and C2, to charge

of charging and discharging continues at a free-running

frequency of 600kHz (typ) until the output has risen to the

upper trip point of COMP2 and the charge pump is

disabled. When the charge pump is disabled, the LTC1516

draws only 8

efficiency at low load conditions.

the LTC1516 operates as either a doubler or a tripler

COMP2 determine whether the charge pump is in doubler

mode or tripler mode. COMP1 forces the part into tripler

is > 2.55V, the part will be in doubler mode using only C2

as a flying capacitor. In doubler mode, if the output droops

by 50mV under heavy loads, COMP3 will force the charge

between 2.5V and 3V.

In shutdown mode, all circuitry is turned off and the part

draws only leakage current (< 1

however, the SHDN pin can be driven by logic levels that

when a logic high is applied to the SHDN pin. The SHDN pin

cannot float; it must be driven with a logic high or low.