LM5145 datasheet(19/62 Pages) TI

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VIN

1.2 V

Enable

comparator

RUV1

RUV2

LM5145-Q1

EN/UVLO

Remote

shutdown

10 A

vcc

Figure 8-3. Programmable Input Voltage UVLO Turn-on and Turn-off

The LM5145-Q1 enters a low IQ shutdown mode when EN/UVLO is pulled below approximately 0.4 V. The

internal LDO regulator powers off and the internal bias supply rail collapses, shutting down the bias currents of

the LM5145-Q1. The LM5145-Q1 operates in standby mode when the EN/UVLO voltage is between the hard

shutdown and precision enable (standby) thresholds.

8.3.5 Power Good Monitor (PGOOD)

The LM5145-Q1 provides a PGOOD flag pin to indicate when the output voltage is within a regulation window.

Use the PGOOD signal as shown in Figure 8-4 for start-up sequencing of downstream converters, fault

protection, and output monitoring. PGOOD is an open-drain output that requires a pullup resistor to a DC supply

not greater than 13 V. The typical range of pullup resistance is 10 kΩ to 100 kΩ. If necessary, use a resistor

divider to decrease the voltage from a higher voltage pullup rail.

LM5145-Q1

1 EN/UVLO

RUV1

499 k

VOUT(MASTER) = 5 V

RFB1

RFB2

20 k

3.83 k

0.8 V

LM5145-Q1

RPG

20 k

RFB3

RFB4

20 k

6.34 k

0.8 V

VOUT(SLAVE) = 3.3 V

VIN(on) = 15 V

VIN(off) = 10 V

Regulator #1

Start-up based on

input voltage UVLO

Regulator #2

Sequential start-up

based on PGOOD

PGOOD 10

RUV2

43.2 k

EN/UVLO

Figure 8-4. Master-Slave Sequencing Implementation Using PGOOD and EN/UVLO

When the FB voltage exceeds 94% of the internal reference VREF, the internal PGOOD switch turns off and

PGOOD can be pulled high by the external pullup. If the FB voltage falls below 92% of VREF, the internal

PGOOD switch turns on, and PGOOD is pulled low to indicate that the output voltage is out of regulation.

Similarly, when the FB voltage exceeds 108% of VREF, the internal PGOOD switch turns on, pulling PGOOD low.

If the FB voltage subsequently falls below 105% of VREF, the PGOOD switch is turned off and PGOOD is pulled

high. PGOOD has a built-in deglitch delay of 25 µs.

8.3.6 Switching Frequency (RT, SYNCIN)

There are two options for setting the switching frequency, FSW, of the LM5145-Q1, thus providing a power supply

designer with a level of flexibility when choosing external components for various applications. To adjust the

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