LTC1516 데이터 시트보기 (PDF) - Linear Technology

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LTC1516

Micropower, Regulated 5V Charge Pump DC/DC Converter

Linear Technology 

LTC1516

BLOCK DIAGRAM

VIN +

10µF

C2+

0.22µF

C2–

C1+

0.22µF

C1–

S2A

S1A

S2B

S1B

S1C

S2C

S1D

COMP1

CLOCK 1

CLOCK 2

CONTROL

LOGIC

COMP2

COMP3

VREF

CHARGE PUMP

CHARGE PUMP SHOWN IN TRIPLER MODE, DISCHARGE CYCLE

SHDN

VOUT

+

10µF

VOS

S3

LTC1516 • BD

APPLICATIONS INFORMATION

Operation

The LTC1516 uses a switched capacitor charge pump to

boost VIN from 2V to 5V to a regulated 5V ±4% output

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

up to the VIN voltage. Clock 2 closes the S2 switches which

stack C1 and C2 in series with VIN and connect the top

plate of C2 to the output capacitor at VOUT. This sequence

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 8µA (typ) from VIN which provides high

efficiency at low load conditions.

To achieve the highest efficiency over the entire VIN range,

the LTC1516 operates as either a doubler or a tripler

depending on VIN and output load conditions. COMP1 and

COMP2 determine whether the charge pump is in doubler

mode or tripler mode. COMP1 forces the part into tripler

mode if VIN is < 2.55V, regardless of output load. When VIN

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

pump into tripler mode until VOUT climbs above the upper

trip point of COMP3. Under these VIN and load conditions,

the nominal VOUT will be approximately 50mV lower than

the no load nominal VOUT. This method of sensing VIN and

output load results in efficiency greater than 80% with VIN

between 2.5V and 3V.

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

draws only leakage current (< 1µA) from the VIN supply.

VOUT is also disconnected from VIN. The SHDN pin is a

CMOS input with a threshold of approximately VIN/2;

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

exceed the VIN voltage. The part enters shutdown mode

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.

4

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