LTM4664 datasheet(29/138 Pages) AD

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POWER GOOD AND UV (PGOODSn AND UVSn PINS)

When the UVSn pin voltage is lower than 1V, the PGOODSn

pin is pulled low. The PGOODSn pin is also pulled low

when the RUNSn pin is low or when the LTM4664A divider

stages are starting up. The PGOODSn pin is released only

when the LTM4664A stage is switching and UVSn pin is

higher than 1V. The PGOODSn pin will flag power bad

immediately when the UVSn pin is low. However, there is

an internal 20μs power good mask and 100mV hystere-

sis when UVSn is higher than 1V. The PGOODSn pin is

pulled up by external resistor to INTVCC. The UVS1 pin

is used to monitor the VOUT1 level for proper regulation,

the PGOODS1 signal is used to sequence on the stage 2's

RUNS2 pin. Then PGOODS2 is used to sequence on the

downstream dual 25A/30A regulators. Proper setup on

the UV pin to set a specific regulation point will release

the PGOODn pin when the output voltage is at that value.

See Figure 1 block diagram.

ADDITIONAL OVERVOLTAGE PROTECTION

The OVP_SET, VOUT2_SET, and OVP_TRIP pins can be

used to monitor the VOUT2 voltage for an overvoltage fault.

These pins can be used in conjunction with the circuit in

Figure 46 to provide a secondary OVP protection in and

above the 4:1 divider fault protection. This feature can be

used to trip off the input power, and further protect the

low voltage outputs.

with a single resistor to GND. The voltage on the FREQSn

pin is equal to the resistance multiplied by 10μA cur-

rent (e.g. the voltage is 1V with a 100k resistor from the

FREQSn pin to GND). A curve is provided below showing

the relationship between the voltages on the FREQSn pin

and switching frequency. Stage 1 is operated at 100kHz,

and Stage 2 is operated at 200kHz for optimal efficiency.

See Figure 4.

LTM4664A

Rev. 0

For more information www.analog.com

FREQ PIN VOLTAGE (V)

1400

1200

800

400

1000

600

200

4664A F04

2.5

1.5

0.5

Figure 4. Relationship Between Switching

Frequency and Voltage at FREQ Pin

fSW (kHz) = RFREQ (kΩ) • 8 – 317kHz

4:1 DIVIDER OPERATION

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