max5932esat Maxim Integrated Products, Inc., max5932esat Datasheet - Page 10

• Manufacturer Part Number: max5932esat
• Description: Max5932 Positive High-voltage, Hot-swap Controller
• Manufacturer: Maxim Integrated Products, Inc.

Positive High-Voltage, Hot-Swap Controller
When circuit boards are inserted into a live backplane,
the supply bypass capacitors on the boards draw high
peak currents from the backplane power bus as they
charge up. The transient currents can permanently
damage the connector pins and glitch the system sup-
ply, causing other boards in the system to reset.
The power supply on a board is controlled by placing
an external n-channel MOSFET (Q1) in the power path
(Figure
and capacitor C1 provides control of the GATE slew
rate. Resistor R6 provides current control-loop compen-
sation while R5 prevents high-frequency oscillations in
Q1. Resistors R1 and R2 provide undervoltage sensing.
After the power pins first make contact, transistor Q1 is
turned off. When the voltage at ON exceeds the turn-on
threshold voltage, the voltage on V
voltage lockout threshold, and the voltage on TIMER is
less than 1.233V, transistor Q1 turns on
The voltage at GATE rises with a slope equal to
10µA/C1 and the supply inrush current is set at:
When the voltage across the current-sense resistor
R
limited by the internal current-limit circuitry that adjusts
the voltage on GATE to maintain a constant voltage
across the sense resistor.
Once the voltage at the output has reached its final value,
as sensed by resistors R3 and R4, PWRGD goes high.
Figure
SENSE
6. Power-Up Waveforms
5). Resistor R
reaches V
POWER-UP WAVEFORMS
I
Applications Information
INRUSH
SENSETRIP
20ms/div
SENSE
= C
L
provides current detection
, then the inrush current is
Hot-Circuit Insertion
Power-Up Sequence
x 10µA/C1
CC
exceeds the under-
(Figure
GATE
50V/div
I
2A/div
OUTPUT
50V/div
PWRGD
50V/div
SENSE
6).
The MAX5932 features a programmable foldback current
limit with an electronic circuit breaker that protects
against short circuits or excessive supply currents. The
current limit is set by placing a sense resistor between
V
To prevent excessive power dissipation in the pass
transistor and to prevent voltage spikes on the input
supply during short-circuit conditions at the output, the
current folds back as a function of the output voltage
that is sensed at FB
When the voltage at FB is 0V, the current-limit circuit
drives GATE to force a constant 12mV drop across the
sense resistor. As the output voltage at FB increases,
the voltage across the sense resistor increases until FB
reaches 0.5V, at the point that the voltage across the
sense resistor is held constant at 47mV.
The maximum current limit is calculated as:
For a 0.025Ω sense resistor, the current limit is set at
1.88A and folds back to 480mA when the output is
shorted to ground.
The MAX5932 also features a variable overcurrent
response time. The time required to regulate Q1’s drain
current depends on:
•
•
•
Figure
until GATE voltage starts falling, as a function of
overdrive.
Figure
CC
Q1’s input capacitance.
GATE capacitor C1 and compensation resistor R6.
The internal delay from SENSE to GATE.
(pin 8) and SENSE (pin 7).
V
47mV
12mV
CC
7. Current-Limit Sense Voltage vs. Feedback Voltage
8 shows the delay from a voltage step at SENSE
- V
0V
SENSE
I
LIMIT
(Figure
= 47mV/R
Short-Circuit Protection
0.5V
7).
SENSE
V
FB