UD24121

LINEAR INTEGRATED CIRCUIT

UNISONICTECHNOLOGIESCO.,LTD

2 of 5

www.unisonic.com.tw

QW-R115-011.E

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MARKING

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PIN CONFIGURATION

BST

GND

FB

SW

IN

EN

1

2

3

5

4

6

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PIN DESCRIPTION

PIN NO.

PIN NAME

DESCRIPTION

1

BST

High-Side Gate Drive Boost Input. BS supplies the drive for the high-side

N-Channel MOSFET switch. Connect a 0.01μF or greater capacitor from SW to

BST to power the high side switch.

2

GND

Ground.

3

FB

Feedback. An external resistor divider from the output to GND, tapped to the FB pin

sets the output voltage. To prevent current limit run away during a short circuit fault

condition, the frequency foldback comparator lowers the oscillator frequency when

the FB voltage is below 250mV.

4

EN

On/Off Control Input. Pull EN above 1.2V to turn the device on. For automatic

enable, connect a 100kΩ resistor between this pin and Vin pin.

5

VIN

Supply Voltage. The UD24121 operates from a +4.5V to +24V unregulated input.

C1 is needed to prevent large voltage spikes from appearing at the input.

6

SW

Power Switching Output. SW is the switching node that supplies power to the

output. Connect the output LC filter from SW to the output load. Note that a

capacitor is required from SW to BS to power the high-side switch.