LTC3252 datasheet(8/14 Pages) AD

8 / 14 page

LTC3290

Rev. 0

For more information www.analog.com

OPERATION (Refer to the Block Diagram)

The LTC3290 is a high voltage boost charge pump that

uses an input power supply and an auxiliary supply to

generate high efficiency boosted output voltages. It sup-

ports a wide input power supply range from 4.5V to 55V

and a wide auxiliary power supply range from 4.5V to 55V

to generate boosted output voltages up to 55V.

Shutdown Mode

In shutdown mode, all circuitry except the internal bias

is turned off. The LTC3290 is in shutdown when a logic

low is applied to the enable input (EN). The LTC3290 only

draws 3µA (typ.) from the VIN supply in shutdown. If the

VAUX pin is tied to VIN it draws an additional 1µA (typ.)

in shutdown.

Charge Pump Operation and VOUT Regulation

The LTC3290 boost charge pump provides low power

BurstMode®operation.Theboostchargepumpandoscilla-

tor circuit are enabled using the EN pin. At the beginning of

a clock cycle, switches S1 and S4 are closed. The external

flying capacitor across the C+ and C– pins is charged to the

VAUXsupply.Inthesecondphaseoftheclockcycle,switches

S1andS4areopened,whileswitchesS2andS3areclosed.

In this configuration the C– side of the flying capacitor is

connected to VIN and charge is delivered through the C+

pin to VOUT. An external resistor divider from VOUT to the

FB and GND pins sets the output voltage at the VOUT pin.

The VOUT output voltage is given by

VOUT = 1V •

+ 1

⎛

⎝

⎜

⎞

⎠

⎟

Once the VOUT voltage reaches its programmed value, the

part shuts down the internal oscillator to reduce switch-

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

referred to as the sleep state in which the part consumes

only about 15µA from the VINpin.Whentheoutputvoltage

droops enough to overcome the burst comparator hys-

teresis, the part wakes up and commences boost charge

pump cycles until the VOUT output voltage exceeds the

VOUT programmed voltage. For low current operation, it

is important to note that the external divider adds a cur-

rent equal to 2 • (1V/R1) to the total quiescent current.

Recommended range of values for R1 is 100k to 500k.

VIN Tracking Mode

The LTC3290 can be configured to set the VOUT voltage

to track the VIN voltage with a fixed offset as shown in

Figure 2.

VOUT

VAUX

CAUX

VSET

CFLY

GND

LTC3290

C–

C+

PGOOD

3290 F02

VAUX

BIAS

VIN

CIN

VIN

COUT

CBIAS

Figure 1. Boost Charge Pump with VOUT Regulation

Figure 2. Boost Charge Pump with VIN Tracking

VOUT

VIN

CIN

VSET

CFLY

GND

LTC3290

C–

C+

PGOOD

3290 F03

VIN

VAUX

BIAS

COUT

CAUX

CBIAS

The VOUT output voltage in this configuration is given by

VOUT = VIN+1V •

⎛

⎝

⎜

⎞

⎠

⎟

In this configuration, the FB pin servos to 1V. This voltage

combined with the external resistor R1 creates a reference

current which is mirrored into the other external resistor

(R2) between the VOUT and VSET pins. The combination

of these two resistors creates a fixed offset voltage above

VIN at the VOUT pin. The magnitude of this offset is set

only by external resistors R1 and R2. The auxiliary sup-

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