ltc4261cgn-trpbf Linear Technology Corporation, ltc4261cgn-trpbf Datasheet - Page 19

• Manufacturer Part Number: ltc4261cgn-trpbf
• Description: Negative Voltage Hot Swap Controllers With Adc And I2c Monitoring
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
present bit A1 and the undervoltage fault bit B1. The
power good signals at PG and PGIO are also reset.
The undervoltage present bit A1 is cleared when the
UVH pin rises above 2.56V and the UVL pin rises above
2.291V + δV
again unless the undervoltage auto-retry has been dis-
abled by clearing bit D1.
When power is applied to the device, if UVL is below
the 2.291V threshold and UVH is below 2.56V – δV
after INTV
(4.25V), an undervoltage fault will be logged in the fault
register.
Because of the compromises of selecting from a table of
discrete resistor values (1% resistors in 2% increments,
0.1% resistors in 1% increments), best possible OV and
UV accuracy is achieved using separate dividers for each
pin. This increases the total number of resistors from
three or four to as many as six, but maximizes accuracy,
greatly simplifi es calculations and facilitates running
changes to accommodate multiple standards or custom-
ization without any board changes.
FET Short Fault
A FET short fault will be reported if the data converter mea-
sures a current sense voltage greater than or equal to 2mV
while the FET is turned off. This condition sets the FET
short present bit A5 and the FET short fault bit B5.
–48V INPUT
–48V RTN
(7a)
R3
453k
1%
R
1.91k
1%
R2
15k
1%
R1
11.8k
1%
H
Figure 7. Adjustment of Undervoltage Thresholds
for Larger (7a) or Smaller (7b) Hysteresis
CC
UVL
UVH
0V
UV
crosses its undervoltage lock out threshold
. After a delay of t
TURN-ON = 46V
TURN-OFF = 38.5V
HYSTERESIS = 7.5V
–48V INPUT
–48V RTN
(7b)
R3
453k
1%
R
1.91k
1%
R2
15k
1%
R1
11.8k
1%
D
H
, the FET will turn on
42612 F07
UVH
UVL
0V
TURN-ON = 43V
TURN-OFF = 41.2V
HYSTERESIS = 1.8V
UV
Power Bad Fault
After the FET is turned on and the power good outputs
pull PG and PGIO low, a delay timer with duration of 4t
started and the level of the PGI pin is checked (Figure 3).
If the PGI pin is pulled below its 1.4V threshold before
the PGI check timer expires, the FET will remain on.
Otherwise, the FET is immediately turned off, the power
good signals are reset and the power bad present bit A3
and the power bad fault bit B3 are set. After the FET is
turned off, the power bad present bit A3 will be cleared.
If the PGI pin is subsequently pulled low, the FET will
remain off unless the power bad auto-retry has been en-
abled by setting bit D4 or the power bad fault bit B3 is
cleared. In either of those two conditions, the FET will
turn on again following a delay of t
checked again as described above.
External Fault Monitors
The FLTIN pin (SSOP only) and the PGIO pin, when con-
fi gured as general purpose input, allow monitoring of ex-
ternal fault conditions such as broken fuses. If FLTIN is
pulled below its 1.4V threshold, bit B7 in the FAULT reg-
ister is set. An associated alert bit, C7, is also available
in the ALERT register. When the PGIO pin is confi gured
as general purpose input, if the voltage at PGIO is above
1.25V, both bit A6 in the STATUS register and bit B6 in
the FAULT register are set, though there is no alert bit as-
sociated with this fault. The external fault conditions do
not directly affect the GATE control functions.
Fault Alerts
When any of the fault bits in FAULT register B is set, an
optional bus alert can be generated by setting the appropri-
ate bit in the ALERT register C. This allows only selected
faults to generate alerts. At power-up the default state is not
to alert on faults. If an alert is enabled, the corresponding
fault will cause the ALERT pin to pull low. After the bus
master controller broadcasts the alert response address,
the LTC4261/LTC4261-2 will respond with its address on
the SDA line and release ALERT as shown in Figure 14.
If there is a collision between two LTC4261’s responding
with their addresses simultaneously, then the device with
LTC4261/LTC4261-2
D
and the PGI pin is
19
42612fb
D
is