SIP1759 datasheet(5/8 Pages) VISHAY

5 / 8 page

Document Number: 72949

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

www.vishay.com

Vishay Siliconix

SiP1759

DESIGNS CONSIDERATIONS

Setting the Adjustable Output Voltage

The SiP1759 regulated output can be adjusted from 2.5 V to

5.5 V via resistor divider network from VOUT to GND (see

Typical Application Circuits). R1 and R2 should be kept in the

50 k

Ω to 100 kΩ range for low power consumption, while

maintaining adequate noise immunity. The value R1 is

calculated using the following formula:

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

VFB is nominally 1.235 V.

Capacitor Selection

Capacitor selection for CIN, COUT and CX will have an impact

in 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 voltage ripple at a

minimum. The initial values for the CIN and COUT capacitors

should be 10 µF, the CX capacitor should be 0.33 µF.

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. Reducing the

CX capacitor value will cause an increase in the switching

frequency and a reduction of the output ripple.

TYPICAL CHARACTERISTICS

Efficiency vs. Input Voltage

Start-Up Input Voltage

100

120

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

Input Voltage (V)

IOUT at 10 mA

IOUT at 50 mA

IOUT at 100 mA

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

Input Voltage (V)

(VOUT < VIN) RLOAD = 33 Ω

Quiescent Current vs. Input Voltage (No Load)

Output voltage Ripple vs. Input Voltage

1.00E-07

1.00E-01

Input Voltage (V)

0.5

1.5

2.5

3.5

5.5

4.5

1.00E-02

1.00E-03

1.00E-04

1.00E-05

1.00E-06

0.00

0.04

0.08

0.12

0.16

0.20

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

Input Voltage (V)

10 mA

50 mA

100 mA

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