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LT3571

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PIN FUNCTIONS

NC (Pin 1): No Connect.

APD (Pin 2): APD Cathode Pin. Connect APD cathode to

this pin.

MONIN (Pin 3): Current Monitor Power Supply Pin. An

external lowpass ﬁlter can be included here to further

reduce supply voltage ripple. This pin also serves as the

inverting input of the current sense ampliﬁer. Put a sense

resistor between the MONIN pin and the VOUT pin to set

the boost converter output current limit as 200mV/RSENSE.

Connect the MONIN pin directly to the VOUT pin if the

output current limit function is not used.

VOUT (Pin 4): Boost Output Pin. Put a capacitor between

this pin and GND plane. Minimize the length of the trace

to the capacitor. Also serves as the noninverting input of

the current sense ampliﬁer.

SW (Pin 5, 6): Switch Pin. Minimize the trace length on

this pin to reduce EMI.

GND (Pin 7, 10): Ground. Pins connected internally. For

best performance, connect both pins to board ground.

SYNC (Pin 8): Frequency Synchronization Pin. Connect an

external clock signal here. RT resistor should be chosen

to program a switching frequency 20% slower than the

SYNC pulse frequency. Synchronization (switch turn-on)

occurs a ﬁxed delay after the rising edge of SYNC. Tie the

SYNC pin to ground if this feature is not used.

RT (Pin 9): Switching Frequency Pin. Set switching fre-

quency using a resistor to GND (see Typical Performance

Characteristics for values). For SYNC function, choose

the resistor to program a frequency 20% slower than the

SYNC pulse frequency. Do not leave this pin open.

VIN (Pin 11): Input Supply Pin. This pin must be locally

bypassed.

SHDN (Pin 12): Shutdown Pin. Tie to 1.5V or higher to

enable device; 0.4V or less to disable device. Also functions

as soft-start. Use RC ﬁlter as shown in Figure 1.

VREF (Pin 13): Reference Output Pin. This pin can supply

up to 100μA. Do not over drive this pin. Bypass with a

10nF or larger capacitor.

CTRL (Pin 14): Internal Reference Override Pin. The CTRL

pin allows the FB voltage to be externally adjusted between

0V and 1V to adjust the output voltage. Tie this pin higher

than 1.2V to use the internal reference of 1V.

FB (Pin 15): Feedback Pin. Connect to output resistor

divider tap.

MON (Pin 16): Current Monitor Output Pin. Sources a

current equal to 20% of the APD current and converts to

a reference voltage through an external resistor.

Exposed Pad (Pin 17): Ground. The Exposed Pad must

be soldered to the PCB.

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