LTC3577 datasheet(24/38 Pages) LINER

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LTC3675

3675fa

OPERATION

data from the selected register. A STOP command is not

required for the bus read operation.

Immediately after writing data to a register, the contents

of that register may be read back if the bus master issues

a START condition followed by the LTC3675 read address.

ERROR CONDITION REPORTING VIA

RSTB AND IRQB PINS

Error conditions are reported back via the IRQB and RSTB

pins. After an error condition is detected, status data can

be read back to a microprocessor via I2C to determine the

exact nature of the error condition.

Figure 4 is a simpliﬁed schematic showing the signal path

for reporting errors via the RSTB and IRQB pins.

All the switching regulators and the LED driver have an

internal power good (PGOOD) signal. When the regulated

output voltage of an enabled switcher rises above 93.5%

of its programmed value, the PGOOD signal will transition

high. When the regulated output voltage falls below 92.5%

of its programmed value, the PGOOD signal is pulled low.

If that PGOOD is not masked and stays low for greater than

50μs, then it pulls the RSTB and IRQB pins low, indicating

to a microprocessor that an error condition has occurred.

The 50μs ﬁlter time prevents the pins from being pulled

low due to a transient.

The LED driver has a PGOOD signal (PGOOD[7]) that

is used to indicate output voltage status only when it is

conﬁgured as a high voltage boost regulator. In all other

operating modes, PGOOD[7] is disabled.

An error condition that pulls the RSTB pin low is not

latched. When the error condition goes away, the RSTB

pin is released and is pulled high if no other error condi-

tion exists.

In addition to the PGOOD signals of the regulators, the

IRQB pin also indicates the status of the overtemperature

and undervoltage ﬂags. The undervoltage and overtem-

perature faults cannot be masked. A fault that causes

the IRQB pin to be pulled low is latched. When the fault

condition is cleared, the IRQB pin is still maintained in its

low state. The user needs to clear the interrupt by using

a CLRINT command.

Figure 4. Simpliﬁed Schematic Showing RSTB and IRQB Signal Path

3675 F04

RSTB MASK REGISTER

PGOOD

COMPARATOR

VOUT

IRQB MASK REGISTER

REGULATOR

92% OF PROGRAMMED VOUT

OTHER UNMASKED

PGOOD OUTPUTS

UNMASKED

PGOOD OUTPUTS

UNMASKED

ERROR

EXTERNAL PULL-UP RESISTOR

VIN

AND1

AND2

OTHER UNMASKED

ERRORS

REAL TIME STATUS REGISTER

LATCHED STATUS REGISTER

SET

CLR

CLRINT

EXTERNAL PULL-UP RESISTOR

IRQB

RSTB

VIN

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