MAX5933A–MAX5933F/MAX5947A/B/C
Positive High-Voltage, Hot-Swap Controllers
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Detailed Description
The MAX5933_ and MAX5947_ are fully integrated hot-
swap controllers for positive supply rails. The devices
allow for the safe insertion and removal of circuit cards
into live backplanes without causing glitches on the
backplane power-supply rail. During startup, the
MAX5933_ and MAX5947_ act as current regulators
using an external sense resistor and a MOSFET to limit
the amount of current drawn by the load.
The MAX5933_ operate from a +33V to +80V supply
voltage range and have a default undervoltage lockout
(UVLO) set to +31V. The MAX5947_ operate from a
+9V to +80V supply voltage range and have a default
UVLO set to +8.3V. The UVLO threshold is adjustable
using a resistive divider connected from V
CC
to ON to
GND (see Figure 5).
The MAX5933_ and MAX5947_ monitor the input volt-
age, the output voltage, the output current, and the die
temperature. These devices feature power-good outputs
(PWRGD/PWRGD) to indicate the status of the output
voltage by monitoring the voltage at FB (see the Power-
Good Detection section).
As shown in Figure 5, a sense resistor is connected
between V
CC
and SENSE to regulate the voltage
across the sense resistor (V
IN
- V
SENSE
) to 47mV when
the voltage at FB ≥ 0.5V. The current-limit threshold
(V
SENSETRIP
) decreases linearly from 47mV to 12mV as
FB decreases from 0.5V to 0V.
An undervoltage fault is detected when ON goes below
the threshold (V
ONL
= 1.233V) and the voltage at GATE
goes low as a result to turn off the MOSFET. ON must
pass the V
ONH
= 1.313V threshold to turn on the
MOSFET again.
