MAX5924/MAX5925/MAX5926
1V to 13.2V, n-Channel Hot-Swap Controllers
Require No Sense Resistor
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Detailed Description
The MAX5924/MAX5925/MAX5926 are hot-swap con-
troller ICs designed for applications where a line card is
inserted into a live backplane. Normally, when a line card
is plugged into a live backplane, the card’s discharged
filter capacitors provide a low impedance that can
momentarily cause the main power supply to collapse.
The MAX5924/MAX5925/MAX5926 are designed to
reside either in the backplane or in the removable card
to provide inrush current limiting and short-circuit pro-
tection. This is achieved using an external n-channel
MOSFET and an optional external current-sense resistor.
Several critical parameters can be configured:
• Slew rate (inrush current)
• Circuit-breaker threshold
• Turn-on voltage
• Fault-management mode (MAX5926)
• Circuit-breaker temperature coefficient (MAX5926)
See the
Selector Guide
for a device-specific list of fac-
tory-preset features and parameters.
Startup Mode
It is important that both V
CC
and V
S
rise at a minimum
rate of 100mV/ms during the critical time when power
voltages are below those values required for proper
logic control of internal circuitry. This applies for 0.5V ≤
V
CC
≤ 2.5V and 0.5V ≤ V
S
≤ 0.8V. This is particularly
true when LATCH is tied high.
The MAX5924/MAX5925/MAX5926 control an external
MOSFET placed in the positive power-supply pathway.
When power is first applied, the MAX5924/MAX5925/
MAX5926 hold the MOSFET off indefinitely if the supply
voltage is below the undervoltage lockout level or if the
device is disabled (see the
EN (MAX5924/MAX5925),
EN1/EN2 (MAX5926)
section). If neither of these condi-
tions exist, the device enters a UVLO startup delay
period for ≈200ms. Next, the MAX5924/MAX5925/
MAX5926 detect whether an external sense resistor is
present; and then autoconfigure accordingly (see
Figure 4).
• If no sense resistor is present, bilevel fault protection
is disabled and load-probing circuitry is enabled
(see the
Load Probing
section).
If load probing is not successful, the fault is man-
aged according to the selected fault management
mode (see the
Latched and Auto-Retry Fault
Management
section).
If load probing (see the
Load Probing
section) is suc-
cessful, slew-rate limiting is employed to gradually
turn on the MOSFET.
• If the device detects an external R
SENSE
, circuit-
breaker threshold is set at 2xI
CB
, the slow compara-
tor is disabled, the startup phase begins without
delay for load probing, and slew-rate limiting is
employed to gradually turn on the MOSFET.
During the startup phase, the voltage at the load, V
OUT
,
rises at a rate determined by the selected slew rate (see
the
Slew Rate
section). The inrush current, I
INRUSH
, to
the load is limited to a level proportional to the load
capacitance, C
L
, and the slew rate:
where SR is the slew rate in V/ms and C
L
is load capac-
itance in µF.
For operation with and without R
SENSE
, once V
GATE
-
V
OUT
exceeds V
CB,EN
, PGOOD and/or PGOOD
assert. When V
GATE
- V
OUT
= V
CB,EN
, the MAX5924/
MAX5925/MAX5926 enable standard bilevel fault pro-
tection with normal I
CB
(see the
Bilevel Fault Protection
section).
