LTC3589-1 datasheet(23/38 Pages) LINER

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LTC3676/LTC3676-1

3676ff

For more information www.linear.com/LTC3676

operaTion

Figure 13. Output Low Voltage PGOOD and IRQ Timing

Figure 12. Power-Down Sequence

300ms

1.2V

WAKE

VB1

VB2

VB3

VB4

VL2

VL3

VL4

1.8V

2.5V

1.2V

1.8V

2.8V

3676 F12

200ms

100ms

FAULT DETECTION AND REPORTING

The LTC3676 has fault detection circuits that monitor

for VIN undervoltage, die overtemperature, and regulator

output undervoltage. Status of the fault detect circuits is

indicated by the IRQ and PGOOD pins and the IRQSTAT

and PGSTAT status registers.

VIN Undervoltage

The undervoltage (UV) circuit monitors the input supply

voltage, VIN, and when the voltage falls below 2.45V cre-

ates a FAULT condition that forces the LTC3676 into the

standby state. The LTC3676 also provides a (UV) warning

that is triggered at user programmable VIN voltages as

shown in Table 11.

Table 11. Undervoltage Warning Threshold Command Register

Settings

COMMAND

VALUE

FALLING VIN THRESHOLD

CNTRL[4:2]

000*

001

010

011

100

101

110

111

2.7V

2.8V

2.9V

3.0V

3.1V

3.2V

3.3V

3.4V

*denotes default power-on value.

450µs

ENx

VOUTx

PGOOD

IRQ

50µs

1ms

20ms

3676 F13

Over Temperature

To prevent thermal damage the LTC3676 incorporates an

overtemperature (OT) circuit. When the die temperature

reaches 155°C the OT circuits create a FAULT condition

that forces the LTC3676 into standby. When the OT cir-

cuit detects the temperature falls below 140°C the FAULT

condition is cleared. The LTC3676 also has an OT warning

circuit that indicates the die temperature is approaching

the OT fault threshold. The OT warning threshold is user

programmable as shown in Table 12.

Table 12. Overtemperature Warning Threshold Command

COMMAND

VALUE

OT WARNING THRESHOLD

CNTRL[1:0]

00*

10°C Below OT Fault

20°C Below OT Fault

30°C Below OT Fault

40°C Below OT Fault

*denotes default power-on value.

PGOOD Status Pin

The PGOOD open-drain status pin is pulled low when all

regulatorsaredisabled.PGOODisreleasedwhenallenabled

regulator outputs are above 93% of programmed value.

When any enabled regulator output falls below 92% of its

programmed value for longer than 50µs the PGOOD pin is

pulled low. The 50µs transient filter on PGOOD prevents

PGOOD glitches due to transients. If the error condition

persistsforlongerthan20ms,theIRQpinispulledlowand

status register IRQSTAT bit 2 is set to indicate a persistent

PGOOD fault. The PGOOD pin is held low for the duration

of the low output condition plus 1ms. Figure 13 shows the

timing of PGOOD during enable and fault events.

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