LT7101 datasheet(9/38 Pages) AD

9 / 38 page

LT7101

Rev. 0

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PIN FUNCTIONS

RUN (Pin 3): Run Control Input. Holding this pin below

1.1V shuts off the switching regulator. Holding this pin

below 0.7V reduces the quiescent current to approxi-

mately 0.7µA. Place a resistor divider between VIN and

this pin to use as an undervoltage lockout. Tie this pin to

VIN to always enable the LT7101.

SGND (Pin 6): Signal Ground.

OVLO (Pin 7): Overvoltage Shutdown Input. If the voltage

on this pin exceeds 1.21V, then the switching regulator

is shut down and the SS pin is internally grounded. Tie

this pin to SGND to allow operation with VIN up to 105V.

RIND (Pin 8): Sets the current used to create an internal

ramp that replicates the inductor current up-slope for low

duty cycle operation. This pin generates a voltage that

varies with the switching frequency. Place a resistor to

SGND on this pin equal to 1/(3.3 • L) to set the internal

ramp current. This pin can be left floating if fixed output

voltage mode is selected using the VPRG1 and VPRG2 pins.

If VPRG1 and VPRG2 are both floating, then a resistor from

RIND to SGND must be used.

ITH (Pin 9): Error Amplifier Output and Switching Regulator

Compensation Point. Place compensation components

between the ITH pin and SGND. Tie this pin to INTVCC for

fixed internal compensation.

VFB (Pin 10): Regulator Feedback Input. When set to

adjustable mode, use an external resistor divider between

the regulator output voltage and the VFB pin. For fixed out-

put voltage mode, tie VFB directly to the regulator output.

FREQ (Pin 11): The frequency control pin for the internal

VCO. Connect this pin to SGND for 300kHz operation or

to INTVCC for 1MHz operation. Place a resistor to SGND

on this pin to set the operating frequency between 200kHz

and 2MHz. Minimize the capacitance on this pin if Burst

Mode operation is used. This pin sources 40µA.

Radiated EMI Performance (CISPR25 Radiated

Emission Test with Class 5 Peak Limits)

TYPICAL PERFORMANCE CHARACTERISTICS T

A = 25°C, unless otherwise noted.

FIGURE 17 CIRCUIT

48VIN TO 5VOUT AT 1A

fSW = 400kHz

VERTICAL POLARIZATION

CLASS 5 PEAK LIMIT

LT7101

FREQUENCY (MHz)

100

200

300

400

500

600

700

800

900

1000

7101 G34

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