LTC3203 datasheet(8/16 Pages) LINER

8 / 16 page

LTC3203/LTC3203-1

LTC3203B/LTC3203B-1

32031fa

The LTC3203/LTC3203-1/LTC3203B/LTC3203B-1 use

a switched capacitor charge pump to boost VIN to a

regulated output voltage. Regulation is achieved by sens-

ing the output voltage through a resistor divider and

modulating the charge pump output current based on the

error signal. A two-phase non-overlapping clock activates

the charge pump switches. The typical frequency of charg-

ing and discharging the flying capacitors is 1MHz

(2x mode) or 0.9MHz (1.5x mode). A unique architecture

maintains relatively constant input current for the lowest

possible input noise.

Mode of Operation

The LTC3203/LTC3203-1/LTC3203B/LTC3203B-1 charge

pump can operate in two modes of voltage conversion:

1.5x or 2x.

In the 1.5x mode the flying capacitors are charged in series

during the first clock phase, and stacked in parallel on top

of VIN on the second clock phase. Alternatively, in the 2x

mode the flying capacitors are charged on alternate clock

phases from VIN. While one capacitor is being charged

from VIN, the other is stacked on top of VIN and connected

to the output. The two flying capacitors operate out of

phase to minimize both input and output ripple. At light

load the LTC3203/LTC3203-1 go into Burst Mode opera-

tion to reduce quiescent current.

The conversion mode should be chosen based on consid-

erations of efficiency, available output current and VOUT

ripple. With a given VIN, the 1.5x mode gives a higher

efficiency but lower available output current. The 2x mode

gives a higher available output current but lower effi-

ciency. Moreover, the output voltage ripple in the 2x mode

is lower due to the out-of-phase operation of the two

flying capacitors.

Generally, at low VIN, the 2x mode should be selected, and

at higher VIN, the 1.5x mode should be selected. By

connecting a resistive divider from VIN to the MODE input

pin the MODE input allows the user to accurately program

the VIN threshold at which the charge pump will switch

from 1.5x mode to 2x mode when VIN starts to fall and

vice versa. Hysteresis on the MODE pin prevents the

LTC3203/LTC3203-1/LTC3203B/LTC3203B-1 from

switching continuously between the two modes.

Output Voltage Programming

The LTC3203-1/LTC3203B-1 has a VSEL input pin that

allows the user to program the regulated output voltage to

either 4.5V or 5V. 4.5V VOUT is useful for driving white

LEDs while a regulated VOUT of 5V is useful for powering

logic circuits.

The LTC3203/LTC3203B has a FB pin in place of the VSEL

pin that allows the output voltage to be programmed using

an external resistive divider.

Shutdown Mode

When SHDN is asserted low, the LTC3203/LTC3203-1/

LTC3203B/LTC3203B-1 enter shutdown mode. The charge

pump is first disabled, but the LTC3203/LTC3203-1/

LTC3203B/LTC3203B-1 continue to draw 5

µA of supply

current. This current will drop to less than 1

µA when VOUT

is fully discharged to 0V. Furthermore, VOUT is discon-

nected from VIN. Since the SHDN pin is a high impedance

CMOS input, it should never be allowed to float.

Burst Mode Operation

The LTC3203/LTC3203-1 provide automatic Burst Mode

operation to reduce quiescent current of the power con-

verter at light loads. Burst Mode operation is initiated if the

output load current falls below an internally programmed

threshold. Once Burst Mode operation is initiated, the part

shuts down the internal oscillator to reduce the switching

losses and goes into a low current state. This state is

referred to as the Sleep state in which the chip consumes

only about 120

µA from the input.

OPERATIO

LTC3203 Datasheet(PDF) 8 Page - Linear Technology

LTC3203 Datasheet(HTML) 8 Page - Linear Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Datasheet Download

Link URL