LTC4260
15
4260fc
For more information
applicaTions inForMaTion
Power Bad Present/Power Bad Fault
When the FB pin drops below its 3.41V threshold the
power bad present bit, C3, goes high. This pulls the GPIO
pin low immediately when configured as PWRGD. If the
FB pin subsequently rises back above the threshold, the
GPIO pin will return to a high impedance state and bit C3
will be cleared.
The power bad fault bit, D3, is set when the GATE-to-
SOURCE voltage is high and the power bad present C3
bit is high. This blanking with the gate voltage prevents
false power bad faults during power-up or power-down.
Fault Alerts
When any of the fault bits in FAULT register D are set,
an optional I
2
C bus alert can be generated by setting the
appropriate bit in the ALERT register B. This allows only
selected faults to generate alerts. At power-up the default
state is to not alert on faults. If an alert is enabled, the cor-
responding fault will cause the
ALERT
pin to pull low. After
the bus master controller broadcasts the Alert Response
Address, the LTC4260 responds with its address on the
SDA line and releases
ALERT
as shown in Figure 11. If
there is a collision between two LTC4260s responding
with their addresses simultaneously, then the device with
the lower address wins arbitration and responds first. The
ALERT
line will also be released if the device is addressed
by the bus master.
–
+
1.235V
GND
MOTHERBOARD
CONNECTOR
PLUG-IN
CARD
SOURCE
OUT
LTC4260
10µA
23
6
BD_PRST 14
C
BD_PRST
LOAD
4260 F04
Figure 4. Plug-In Card Insertion/Removal
Once the
ALERT
signal has been released for one fault,
it will not be pulled low again until the FAULT register
indicates a different fault has occurred or the original
fault is cleared and it occurs again. Note that this means
repeated or continuing faults will not generate alerts until
the associated FAULT register bit has been cleared.
Resetting Faults
Faults are reset with any of the following conditions. First,
a serial bus command writing zeros to the FAULT register
D will clear the associated faults. Second, the entire FAULT
register is cleared when the switch is turned off by either
the ON pin or bit A3 going from high to low, or if the UV
pin is brought below its 1.23V reset threshold, or if INTV
CC
falls below its 3.8V undervoltage lockout threshold. Finally,
when
BDPRST
is brought from high to low, only FAULT
bits D0-D3 and D5 are cleared, the bit D4 that indicates a
BDPRST
change of state will be set. Faults that are still
present (as indicated in the STATUS Register C) cannot
be cleared.
The FAULT register will not be cleared when autoretrying.
When autoretry is disabled the existence of a D0, D1 or D2
fault keeps the switch off. As soon as the fault is cleared,
the switch will turn on. If autoretry is enabled, then a high
value in C0, C1 or C2 will hold the switch off and the FAULT
register is ignored. Subsequently, when the C0, C1 and
C2 bits are cleared, the switch is allowed to turn on again.
Data Converter
The LTC4260 incorporates an 8-bit data converter that
continuously monitors three different voltages. The Δ∑
architecture inherently averages signal noise during the
measurement period. The SOURCE pin uses a 1/40 resis-
tive divider to monitor a full-scale voltage of 102.4V with
0.4V resolution (divider converts 102.4V to 2.56V). The
ADIN pin is monitored with a 2.56V full scale and 10mV
resolution, and the voltage between the V
DD
and SENSE
pins is monitored with a 76.8mV full scale and 300µV
resolution.
The results from each conversion are stored in registers
E, F and G and are updated 10 times per second. Setting
CONTROL register bit A5 invokes a test mode that halts
the data converter updates so that registers E, F and G
can be written to and read from for software testing.
