LM3481MM datasheet(13/30 Pages) TI1

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R7 =

-1

VEN

1.43V

R8 =

1 +

1.43V ± VSH

VEN ± 1.43V

IUVLO

1.43V

FA/SYNC/SD

40 k:

30 Ps

LM3481

FA/SYNC/SD

>1.3V

10 k:

RFA

MOSFET State

On-Normal Operation

OFF- Shutdown

LM3481

FA/SYNC/SD

Freq. clock

100 kHz to 1 MHz

RFA

LM3481

www.ti.com

SNVS346E – NOVEMBER 2007 – REVISED APRIL 2012

Figure 25. Frequency Synchronization

Figure 26. Shutdown Operation in Frequency Adjust Mode

Figure 27. Shutdown Operation in Synchronization Mode

UNDER VOLTAGE LOCKOUT (UVLO) Pin

The UVLO pin provides user programmable enable and shutdown thresholds. The UVLO pin is compared to an

internal reference of 1.43V (typical), and a resistor divider programs the enable threshold, VEN. When the IC is

enabled, a 5

μA current is sourced out of the UVLO pin, which effectively causes a hysteresis, and the UVLO

shutdown threshold, VSH, is now lower than the enable threshold. Setting these thresholds requires two resistors

connected from the VIN pin to the UVLO pin and from the UVLO pin to GND (see Figure 28). Select the desired

enable, VEN, and UVLO shutdown, VSH, threshold voltages and use the following equations to determine the

resistance values:

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