Datasheet

LTC3676/LTC3676-1
22
3636fa
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
V
B1
V
B2
V
B3
V
B4
V
L2
V
L3
V
L4
1.8V
2.5V
1.2V
1.2V
1.8V
2.8V
3676 F12
200ms
100ms
FAULT DETECTION AND REPORTING
The LTC3676 has fault detection circuits that monitor
for V
IN
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.
V
IN
Undervoltage
The undervoltage (UV) circuit monitors the input supply
voltage, V
IN
, 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 V
IN
voltages as
shown in Table 11.
Table 11. Undervoltage Warning Threshold Command Register
Settings
COMMAND
REGISTER[BIT] VALUE FALLING V
IN
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
V
OUTx
PGOOD
IRQ
50µs
50µs
1ms
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
Register Settings
COMMAND
REGISTER[BIT] VALUE OT WARNING THRESHOLD
CNTRL[1:0] 00*
01
10
11
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
regulators are disabled. PGOOD is released when all enabled
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
persists for longer than 20ms, the IRQ pin is pulled low and
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.