Datasheet

LTC3675/LTC3675-1
24
36751fc
For more information www.linear.com/LTC3675
operaTion
is acknowledged by the LTC3675/LTC3675-1. After receiv-
ing the acknowledge signal from the LTC3675/LTC3675-1
the bus master initiates a new START condition followed
by the LTC3675/LTC3675-1 read address. The LTC3675/
LTC3675-1 acknowledge the read address and then return
a byte of read back 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/LTC3675-1
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 I
2
C 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
Figure 4. Simplified Schematic Showing RSTB and IRQB Signal Path
36751 F04
RSTB MASK REGISTER
PGOOD
COMPARATOR
V
OUT
IRQB MASK REGISTER
REGULATOR
92% OF PROGRAMMED V
OUT
OTHER UNMASKED
PGOOD OUTPUTS
UNMASKED
PGOOD OUTPUTS
UNMASKED
ERROR
EXTERNAL PULL-UP RESISTOR
V
IN
+
–
AND1
AND2
OTHER UNMASKED
ERRORS
REAL TIME STATUS REGISTER
LATCHED STATUS REGISTER
SET
CLRCLRINT
EXTERNAL PULL-UP RESISTOR
IRQB
RSTB
V
IN