KB3440EMS datasheet(6/20 Pages) KINGBOR

6 / 20 page

RT (Pin 1): Timing Resistor to Program the Oscillator

Frequency. The programming frequency range is 300kHz

to 2MHz.

OSC

61010

•

MODE/SYNC (Pin 2): MODE/SYNC = External CLK : Syn-

chronization of the internal oscillator. A clock frequency of

twice the desired switching frequency and with a pulse

width between 100ns and 2

µs is applied. The oscillator

free running frequency is set slower than the desired

synchronized switching frequency to guarantee sync. The

oscillator RT component value required is given by:

81010

•

where fSW = desired synchronized switching frequency.

SW1 (Pin 3): Switch Pin Where the Internal Switches A

and B are Connected. Connect inductor from SW1 to SW2.

An optional Schottky diode can be connected from SW1 to

ground. Minimize trace length to keep EMI down.

SW2 (Pin 4): Switch Pin Where the Internal Switches C

and D are Connected. For applications with output volt-

ages over 4.3V, a Schottky diode is required from SW2 to

VOUT to ensure the SW pin does not exhibit excess voltage.

GND (Pin 5): Signal and Power Ground for the IC.

VOUT (Pin 6): Output of the Synchronous Rectifier. A filter

capacitor is placed from VOUT to GND.

VIN (Pin 7): Input Supply Pin. Internal VCC for the IC. A

ceramic bypass capacitor as close to the VIN pin and GND

(Pin 5) is required.

SHDN/SS (Pin 8): Combined Soft-Start and Shutdown.

Grounding this pin shuts down the IC. Tie to >1.5V to

enable the IC and > 2.5V to ensure the error amp is not

clamped from soft-start. An RC from the shutdown com-

mand signal to this pin will provide a soft-start function by

limiting the rise time of the VC pin.

FB (Pin 9): Feedback Pin. Connect resistor divider tap

here. The output voltage can be adjusted from 2.5V to

5.5V. The feedback reference voltage is typically 1.22V.

VC (Pin 10): Error Amp Output. A frequency compensation

network is connected from this pin to the FB pin to

compensate the loop. See the section “Compensating the

Feedback Loop” for guidelines.

Exposed Pad (Pin 11, DFN Package Only): Ground. This

pin must be soldered to the PCB and electrically connected

to ground.

kB3440

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