Datasheet

MAX5924/MAX5925/MAX5926
1V to 13.2V, n-Channel Hot-Swap Controllers
Require No Sense Resistor
12 ______________________________________________________________________________________
Load Probing
The MAX5924/MAX5925/MAX5926 load-probing circuit-
ry detects short-circuit conditions during startup. Load
probing is active only when no external R
SENSE
is
detected. As the device begins load probing, SC_DET
is connected to V
CC
through an internal switch with an
on-resistance of R
LP
(Figure 6). V
CC
then charges the
load with a probe current limited at ≈200mA.
I
PROBE
= (V
CC
- V
OUT
)/(R
LP
+ R
SC
) (Figure 1)
If the load voltage does not reach V
LP,TH
(0.2V typ)
within t
LP
, a short-circuit fault is detected and the start-
up mode is terminated according to the selected fault-
management mode (see the
Fault Management section
and Figure 5). If no fault condition is present,
PGOOD/PGOOD asserts at the end of the startup peri-
od (see the Turn-On Waveforms in the
Typical
Operating Characteristics ).
Load probing can only be, and must be, employed
when not using an external R
SENSE
.
Normal Operation
In normal operation, after startup is complete, protec-
tion is provided by turning off the external MOSFET
when a fault condition is encountered. Dual-speed/
bilevel fault protection incorporates two comparators
with different thresholds and response times to monitor
the current:
1) Slow comparator. This comparator has a 1.6ms
(typ) response time. The slow comparator ignores
low-amplitude momentary current glitches. After an
extended overcurrent condition, a fault is acknowl-
edged and the MOSFET gate is discharged.
2) Fast comparator. This comparator has a quick
response time and a higher threshold voltage. The
fast comparator turns off the MOSFET immediately
when it detects a large high-current event such as a
short circuit.
In each case, when a fault is encountered, the power-
good output deasserts and the device drives GATE low.
After a fault, the MAX5924A, MAX5924B, MAX5925A,
and MAX5925B latch GATE low and the MAX5924C,
MAX5924D, MAX5925C, and MAX5925D enter the
autoretry mode. The MAX5926 has selectable latched or
autoretry modes. Figure 7 shows the slow comparator
response to an overcurrent fault.
V
CC
(V)
R
LP
(Ω)
1210864
6
8
10
12
14
4
214
V
CC
= V
S
Figure 6. Load-Probe Resistance vs. Supply Voltage
V
GATE
PGOOD*
V
OUT
I
LOAD
I
LIM
3.0V TO 6.7V
PGOOD**
*MAX5924B, MAX5924D, MAX5925B, MAX5925D, AND MAX5926 ONLY.
**MAX5924A, MAX5924C, MAX5925A, MAX5925C, AND MAX5926 ONLY.
t
CBS
V
THPGOOD
Figure 7. Slow Comparator Response to an Overcurrent Fault
t
PROBE
< t
LP
I
INRUSH
C
L
= LARGE
C
L
= SMALL
V
OUT
V
OUT
I
LOAD
I
LOAD
I
PROBE
V
LP,TH
(0.2V typ)
SR = dV
dt
C
L
= SMALL
SR = dV
dt
Figure 5. Startup Waveform