Kingbor Technology Co.,Ltd
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kB3440
PIN FUNCTIONS
RT (Pin 1): Timing Resistor to Program the Oscillator ages over 4.3V, a Schottky diode is required from SW2 to
Frequency. The programming frequency range is 300kHz
to 2MHz.
VOUT toensuretheSWpindoesnotexhibitexcessvoltage.
GND (Pin 5): Signal and Power Ground for the IC.
6• 1010
VOUT (Pin 6): Output of the Synchronous Rectifier. A filter
capacitor is placed from VOUT to GND.
fOSC
=
Hz
RT
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.
MODE/SYNC (Pin 2): MODE/SYNC = External CLK : Syn-
chronizationoftheinternaloscillator. Aclockfrequencyof
twice the desired switching frequency and with a pulse
width between 100ns and 2µs 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:
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.
8•1010
fSW
RT =
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.
where fSW = desired synchronized switching frequency.
SW1 (Pin 3): Switch Pin Where the Internal Switches A
andBareConnected. ConnectinductorfromSW1toSW2.
An optional Schottky diode can be connected from SW1 to
ground. Minimize trace length to keep EMI down.
VC (Pin10):ErrorAmpOutput.Afrequencycompensation
network is connected from this pin to the FB pin to
compensate the loop. See the section “Compensating the
Feedback Loop” for guidelines.
SW2 (Pin 4): Switch Pin Where the Internal Switches C
and D are Connected. For applications with output volt-
Exposed Pad (Pin 11, DFN Package Only): Ground. This
pinmustbesolderedtothePCBandelectricallyconnected
to ground.
6
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