LTC3458LEDE datasheet(7/16 Pages) LINER

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LTC3458L

3458lf

PI FU CTIO S

SW (Pin 1): Switch Pin for Inductor Connection. During

discontinuous conduction mode an antiring resistor con-

nects SW to VIN to reduce noise.

VIN (Pin 2): Input Supply Pin. Connect this to the input

supply and decouple with 1

µF minimum.

SYNC (Pin 3): Oscillator Synchronization Pin. A clock

pulse width of 100ns to 2

µs is required to synchronize the

internal oscillator. This pin is disabled when grounded.

SHDN (Pin 4): Shutdown Pin. Grounding this pin shuts

down the IC. Connect to >1.25V to enable.

ILIM (Pin 5): Adjustable Peak Current Limit. Connect a

resistor from ILIM to GND to program the peak inductor

current according to the following formula:

LIMIT

ILIM

180

where ILIMIT is in amps and RT is in kΩ.

RT (Pin 6): Connect a resistor to ground to program the

oscillator frequency, according to the formula:

OSC

02 0004

•

where fOSC is in MHz and RT is in kΩ.

Oscillator frequency can be programmed between 400kHz

and 1.5MHz.

FB (Pin 7): Connect Resistor Divider Tap Here. The output

voltage can be adjusted from 2V to 6V. Feedback reference

voltage is typically 1.225V.

COMP (Pin 8): gm Error Amp Output. A frequency com-

pensation network is connected from this pin to ground to

compensate the loop. See the section “Compensating the

Feedback Loop” for guidelines.

GND (Pin 9): Signal Ground Pin.

SS (Pin 10): Connect a capacitor between this pin and

ground to set soft-start period. 5

µA of current is sourced

from SS during soft-start.

t(msec) = CSS (µF )• 200

BURST (Pin 11): Burst Mode Threshold Adjust Pin. A

resistor/capacitor combination from this pin to ground

programs the average load current at which automatic

Burst Mode operation is entered, according to the formula:

BURST

where RBURST is in kΩ and IBURST is in amps.

BURST

OUT

•

10 000

where CBURST(MIN) and COUT are in µF.

To force fixed frequency PWM mode, connect BURST to

VOUT through a 51k resistor.

VOUT (Pin 12): Output of the Synchronous Rectifier and

Internal Gate Drive Source for the Power Switches.

OUT =+

⎛

⎝⎜

⎞

⎠⎟

1 225 1

Exposed Pad (PGND) (Pin 13): Must be soldered to PCB

ground, for electrical contact and optimum thermal

performance.

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