SIP1759DB datasheet(3/5 Pages) VISHAY

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Document Number: 73784

S-61383–Rev. A, 31-Jul-06

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Vishay Siliconix

SiP1759DB

CHOICE OF COMPONENTS

Output Voltage

The SiP1759 regulated output is set at 2.5 V for ship-

ment. It can be adjusted from 2.5 V to 5.5 V via resistor

divider network from VOUT to GND. R1 and R2 should

be kept in the 50 k

Ω to 100 kΩ range for low power

consumption, while maintaining adequate noise immu-

nity. The value R1 is calculated using the following for-

mula:

R1 = R2((VOUT/VFB)-1)

VFB is nominally 1.235 V.

Capacitor Selection

The value for the CIN and COUT capacitors is 10 µF and

the value of the CX capacitor is 0.33 µF.

Capacitor selection for CIN, COUT and CX will have an

impact on the voltage output ripple, output current and

overall physical size of the circuit.

Ceramic capacitors are recommenced for their low

ESR, (

≤ 20 mΩ), which will help keep the output volt-

age ripple at a minimum.

Output Voltage Ripple

The SiP1759 automatically decides whether to be in

step up mode or step down mode depending on the

VIN, VOUT and current load conditions, therefore the

voltage output ripple will vary. In step-up mode the

voltage output ripple is higher than step-down mode.

But unless VIN is significant larger than VOUT

(VIN ≥ VOUT + 1 V), in heavy load the IC will slip from

buck mode to boost mode as necessary to charge the

transfer capacitor and the ripple will increase. Reduc-

ing the CX capacitor value will cause an increase in the

swit-ching frequency and a reduction of the output rip-

ple.

PRINTED CIRCUIT BOARD

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