Dual, 7.5V to 76V, Hot-Swap and
Diode ORing Controller
14   ______________________________________________________________________________________
An external resistor connected to TCL and an internal
1/128 integrating counter determines the current-limit
timeout. If the current-limit threshold is exceeded for
more than roughly 100ns (comparator and logic
delays), the timer counts up. Note that multiple consec-
utive overcurrent occurrences may cause the current-
limit timer to trip (Figure 2).
During an output short-circuit event or a gross over-
load, the load current overshoots and causes V
SENSE_
to exceed the fast pulldown current-limit threshold volt-
age (V
THF
). The MAX5963 responds with much
stronger GATE_ pulldown currents (I
GDP_
and/or I
GDF_
)
to quickly bring the load current back down to the pro-
grammed current limit.
In extreme cases where V
SENSE_
is less than V
PS
by
more than 700mV (typ), the MAX5963 immediately pulls
GATE1_ and GATE2_ low with a 1A (typ) peak pulldown
current to disconnect the load from the power supply.
Following an overcurrent event, the gates of the exter-
nal MOSFETs are held low (latched) if the device is in
latchoff mode. Toggle ON_ to restart the device under
these conditions. If RETRY is pulled high or connected
to BP or PS, the device pulls the gates high again fol-
lowing the automatic restart delay t
OFFCL
.
Current-Limit Threshold
The MAX5963 features adjustable current limits for
channel A and channel B. Set the current-limit threshold
voltage (V
CL_TH
) for both channels by connecting a
resistor, R
CL
, from CL to PS. Calculate V
CL_TH
using
the following equation:
V
CL_TH
= I
CLSET
x R
CL
where I
CLSET
is the 100礎(chǔ) (typ) current-limit set current
shown in the Electrical Characteristics table.
Connect a sense resistor (R
SENSE_
) between PS and
SENSE_ to set the individual current limits for channel A
and channel B. Calculate the required sense resistor for
each channel using the following equation:
where I
CL_LIMIT
is the maximum channel current limit.
Current-Limit Timeout
The MAX5963 autoretry feature attempts to restart the
device following the adjustable current-limit timeout,
limiting the duty cycle of the MOSFETs under continu-
ous fault conditions. The autoretry timeout is equal to
128 times the current-limit timeout:
t
OFFCL
(ms) = 128 x t
CL
(ms)
Set the current-limit timeout from 1ms to 30ms by con-
necting a resistor between TCL and ground. See Figure 3
for resistor values and associated timeouts. Connect TCL
to BP to select the 1ms (typ) default current-limit timeout.
Circuit Breaker
The MAX5963 features internal circuit-breaker circuitry
that functions as a current monitor. Once the output
current exceeds the circuit-breaker limit (I
CB_LIMIT
), the
circuit-breaker timer begins. When the circuit-breaker
timeout (t
CB
) is reached, GATE_ is pulled low and a
fault condition is asserted (Figure 1).
An external resistor connected to TCB and an internal
1/1 integrating counter determines the circuit-breaker
timeout. If the circuit-breaker threshold is exceeded for
more than roughly 100ns (comparator and logic
delays), the timer counts up. Note that multiple consec-
utive circuit-breaker overcurrent occurrences may
cause the circuit-breaker timer to trip (Figure 4).
Following a circuit-breaker event, the gates of the exter-
nal MOSFETs are held low (latched) if the device is in
latchoff mode. If RETRY is pulled high or connected to
BP, the device pulls the gates high again following the
automatic restart delay t
OFFCB
.
R
V
I
SENSE_
CL_TH
CL_LIMIT
=
CURRENT-LIMIT
TRIPS
t
t
t
CL
t
CL
I
CL
I
OUT_
SLOPE = -1/128
SLOPE = 1
TIMER
Figure 2: Current-Limit Timeout Following Consecutive
Overcurrent Events