LTC3375 datasheet(23/36 Pages) LINER

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LTC3375

3375fa

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operaTion

An error condition that pulls the RST pin low is not latched.

Whentheerrorconditiongoesaway,theRSTpinisreleased

and is pulled high if no other error condition exists.

In addition to the PGOOD signals of the regulators the

IRQ pin also indicates the status of the pushbutton, die

temperature, and undervoltage flags. Pushbutton faults

cannot be masked. A fault that causes the IRQ pin to be

pulled low is latched with the exception of a pushbutton

pressthatislessthan10seconds(CT=0.01µF)whileONis

HIGH. In the case of a transient pushbutton press IRQ will

be held LOW for the duration of the button press latching

after the 10 second power-down time has elapsed. In all

other cases when the fault condition is cleared, the IRQ

pin is still maintained in its low state. The user needs to

clear the interrupt by using a CLRINT command.

On start-up, all PGOOD status outputs are unmasked with

respect to RST. While all PGOOD and UVLO status outputs

are masked with respect to IRQ. A power-on reset will

cause RST to be pulled low. Once all enabled regulators

have their output PGOOD for 230ms typical (CT = 0.01µF)

the RST output goes Hi-Z.

BymaskingaPGOODsignal,theRSTorIRQpinwillremain

Hi-Z even though the output voltage of a regulator may be

below its PGOOD threshold. By masking a UVLO signal,

the IRQ pin will remain Hi-Z even though its associated

input voltage may be below its UVLO threshold. However,

when the status registers are read back, the true condi-

tions of PGOOD and UVLO are reported. If a UVLO IRQ is

masked but the associated PGOOD signal is unmasked,

then the IRQ pin may still be pulled low due to a PGOOD

LOW signal that resulted from an input UVLO.

Temperature Monitoring and

Overtemperature Protection

To prevent thermal damage to the LTC3375 and its sur-

rounding components, the LTC3375 incorporates an

overtemperature (OT) function. When the LTC3375 die

temperature reaches 165°C (typical) all enabled buck

switching regulators are shut down and remain in shut-

down until the die temperature falls to 155°C (typical).

The LTC3375 also has a die temperature warning function

which warns a user that the die temperature has reached

its programmed alarm threshold which allows the user to

take any corrective action. The die temperature warning

threshold is user programmable as shown in Table 2.

3375 F04

RST MASK REGISTER

PGOOD

COMPARATOR

VOUT

IRQ MASK REGISTER

REGULATOR

92.5% OF PROGRAMMED VOUT

OTHER UNMASKED

PGOOD OUTPUTS

UNMASKED

PGOOD OUTPUTS

UNMASKED

ERROR

EXTERNAL PULL-UP RESISTOR

AND1

AND2

OTHER UNMASKED

ERRORS

IRQ STATUS REGISTER

SET

CLR

CLRINT

EXTERNAL PULL-UP RESISTOR

IRQ

RST

VCC

Figure 4. Simplified Schematic RST and IRQ Signal Path

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