max5939eesat Maxim Integrated Products, Inc., max5939eesat Datasheet - Page 11

• Manufacturer Part Number: max5939eesat
• Description: -48v Hot-swap Controllers With External Rsense And High Gate Pulldown Current
• Manufacturer: Maxim Integrated Products, Inc.

Figure 7. Short-Circuit Protection Waveform
Figure 10 shows how to program the undervoltage and
overvoltage trip thresholds using three resistors. With R4
= 549kΩ, R5 = 6.49kΩ, and R6 = 10kΩ, the undervolt-
age threshold is set to 38.5V (with a 43V release from
undervoltage), and the overvoltage is set to 71V. The
resistor-divider also increases the hysteresis and over-
voltage lockout to 4.5V and 2.8V at the input supply,
respectively.
Use the PWRGD (PWRGD) output to enable a power
module after hot insertion. Use the MAX59__A (PWRGD)
to enable modules with an active-low enable input
(Figure 12), or use the MAX59__B (PWRGD) to enable
modules with an active-high enable input (Figure 11).
The PWRGD signal is referenced to the DRAIN termi-
nal, which is the negative supply of the power module.
The PWRGD signal is referenced to V
When the DRAIN voltage of the MAX5921A (see
Selector Guide for complete selection) or MAX5939A is
high with respect to V
from an undervoltage condition, then the internal pull-
down MOSFET Q2 is off. The PWRGD output goes into
a high-impedance state (Figure 13). PWRGD is pulled
high by the module’s internal pullup current source,
turning the module off. When the DRAIN voltage drops
below V
∆V
enabling the module.
The PWRGD signal can also be used to turn on an LED
GATE
DL
- V
GH
and the GATE voltage is greater than
, Q2 turns on and PWRGD pulls low,
-48V Hot-Swap Controllers with External
______________________________________________________________________________________
R
SENSE
1ms/div
EE
PWRGD /PWRGD Output
or the GATE voltage is low
EE
and High Gate Pulldown Current
.
DRAIN
50V/div
GATE - V
10V/div
INRUSH
CURRENT
5A/div
EE
or optoisolator to indicate that the power is good (Figure
13) (see the Component Selection Procedure section).
When the DRAIN voltage drops below V
GATE voltage is greater than ∆V
Q3 turns on, shorting I
pullup current in the module pulls the PWRGD high,
enabling the module.
When the DRAIN voltage of the MAX5921B/MAX5939B
(see Selector Guide for complete selection) is high with
respect to V
due to an undervoltage condition, the internal MOSFET
Q3 is turned off so that I
clamp PWRGD to the DRAIN turning off the module.
Once the PWRGD and PWRGD outputs are active, the
MAX5921/MAX5939 output does not toggle due to an
overvoltage (OV) fault.
GATE goes high when the following startup conditions
are met: UV is high, OV is low, the supply voltage is
above V
The gate is pulled up with a 45µA current source and is
regulated at 13.5V above V
include an internal clamp that ensures the GATE voltage
of the external MOSFET never exceeds 18V. During a
fast-rising V
GATE and SENSE potentials as close as possible to pre-
vent the FET from accidentally turning on. When a fault
condition is detected, GATE is pulled low (see the Load
Current Regulation section).
Figure 8. Voltage Step-On Input Supply
UVLOH
DD
EE
, an additional dynamic clamp keeps the
, and (V
(Figure 12) or the GATE voltage is low
400µs/div
1
GATE Voltage Regulation
SENSE
to V
1
and the internal MOSFET Q2
EE
EE
- V
. The MAX5921/MAX5939
and turning Q2 off. The
EE
GATE
) is less than 50mV.
- V
V
20V/div
DRAIN
20V/div
I
2A/div
D
EE
(Q1)
GH
DL
, MOSFET
and the
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