SIP1759 datasheet(4/8 Pages) VISHAY

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Document Number: 72949

S09-1453-Rev. D, 03-Aug-09

Vishay Siliconix

SiP1759

FUNCTIONAL BLOCK DIAGRAM

DETAILED DESCRIPTION

The SiP1759 is a buck-boost regulating charge pump. This

allows for the VIN to be a higher or lower voltage than the

regulated output. This is done with a charge pump that when

VIN is lower than VOUT is a regulated voltage doubler. When

VIN is higher than VOUT the charge pump is a step down

gated switch.

In boost mode, the IC controls the transfer capacitor through

CX+ and CX- pins, switching the charge to the output keeping

it regulated. In this mode the charge pump only switches to

maintain regulation, the output ripple does not increase with

light loads. In buck mode, the CX- pin is internally connected

to PGND and the CX+ is switched internally between VIN and

VOUT. Unless VIN is significantly larger than VOUT (VIN ≥

VOUT + 1 V), in heavy load the IS will slip from buck mode to

boost mode as necessary to charge the transfer capacitor.

Shutdown Mode

The IC is designed to conserve power by decreasing current

consumption during normal operation as well as shutdown

mode. Pulling the SD pin logic low, the output is

disconnected from the input and is in high impedance; the

internal circuitry of the oscillator, control logic, and the

charge-pump switches are turned off, decreasing the current

consumption to less than 1 µA.

Undervoltage Lockout

When VIN falls below 1 V the undervoltage lockout disables

the SiP1759.

Power OK Output

POK is an open-drain output that goes low when the

regulator feedback voltage falls below 1.1 V. A 10 k

Ω to 1 MΩ

pull-up resistor from POK to OUT should be used to provide

a logic output and keep current consumption to a minimum.

Connect POK to GND or leave floating if not used. The POK

output is high impedance when the IC is in shutdown mode.

Fixed Output

The SiP1759 can be configured as a fixed 3.3 V output

regulator or as an adjustable output from 2.5 V to 5.5 V. In

the fixed 3.3 V output mode the feedback voltage is

generated from the internal resistor-divider network. The FB

pin must be tied to GND.

Soft-Start and Short Circuit Protection

The IC features a soft-start mechanism that limits the inrush

current during start-up and if the output is short circuited the

SiP1759 limits the output current to 110 mA.

Thermal Shutdown

The SiP 1759 is designed with a thermal shutdown circuit

that will shut down the IC when the die temperature exceeds

160 °C. The thermal shutdown has 20 °C of hysteresis,

insuring when the die cools down the IC will turn on again.

Oscillator

Control

Bias

VIN

PGND

ERROR

GND

VOUT

CX+

CX-

1.235 V

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