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PDF MAX5939 Data sheet ( Hoja de datos )
| Número de pieza | MAX5939 | |
| Descripción | -48V Hot-Swap Controllers | |
| Fabricantes | Maxim Integrated | |
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19-2946; Rev 1; 2/06
-48V Hot-Swap Controllers with External
RSENSE and High Gate Pulldown Current
General Description
The MAX5921/MAX5939 hot-swap controllers allow a cir-
cuit card to be safely hot plugged into a live backplane.
The MAX5921/MAX5939 operate from -20V to -80V and
are well suited for -48V power systems. These devices
are pin compatible with both the LT1640 and LT4250 and
provide improved features over these devices.
The MAX5921/MAX5939 provide a controlled turn-on to
circuit cards preventing damage to board connectors,
board components, and preventing glitches on the
power-supply rail. The MAX5921/MAX5939 provide
undervoltage, overvoltage, and overcurrent protection.
These devices ensure that the input voltage is stable
and within tolerance before applying power to the load.
Both the MAX5921 and MAX5939 protect a system
against overcurrent and short-circuit conditions by turn-
ing off the external MOSFET in the event of a fault con-
dition. The MAX5921/MAX5939 protect against input
voltage steps by limiting the load current to a safe level
without turning off power to the load.
The device features an open-drain power-good status
output, PWRGD or PWRGD for enabling downstream
converters (see Selector Guide). A built-in thermal shut-
down feature is also included to protect the external
MOSFET in case of overheating. The MAX5939 features
a latched fault output. The MAX5921 contains built-in
autoretry circuitry after a fault condition.
The MAX5921/MAX5939 are available in an 8-pin SO
package and operate in the extended -40°C to +85°C
temperature range.
Applications
Telecom Line Cards
Network Switches/Routers
Central-Office Line Cards
Server Line Cards
Base-Station Line Cards
Features
♦ Allows Safe Board Insertion and Removal
from a Live -48V Backplane
♦ Pin-Compatible with LT1640 and LT4250
♦ Circuit Breaker Immunity to Input Voltage Steps
and Current Spikes
♦ 450mA GATE Pulldown Current During Short-
Circuit Condition
♦ Exponential GATE Pulldown Current
♦ Withstands -100V Input Transients with No
External Components
♦ Programmable Inrush and Short-Circuit Current
Limits
♦ Operates from -20V to -80V
♦ Programmable Overvoltage Protection
♦ Programmable Undervoltage Lockout
with Built-In Glitch Filter
♦ Overcurrent Fault Integrator
♦ Powers Up into a Shorted Load
♦ Power-Good Control Output
♦ Thermal Shutdown Protects External MOSFET
Ordering Information
PART
MAX5921AESA
MAX5921BESA
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
8 SO
8 SO
Ordering Information continued at end of data sheet.
TOP VIEW
Pin Configuration
Typical Operating Circuit and Selector Guide appear at end
of data sheet.
PWRGD
(PWRGD) 1
OV 2
UV 3
VEE 4
MAX5921
MAX5939
8 VDD
7 DRAIN
6 GATE
5 SENSE
SO
() FOR MAX5921B/F AND MAX5939B/F.
________________________________________________________________ Maxim Integrated Products 1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
1 page  
-48V Hot-Swap Controllers with External
RSENSE and High Gate Pulldown Current
R
5kΩ
V+
5V
PWRGD/PWRGD
VDD
OV DRAIN
VOV MAX5921
MAX5939
UV GATE
VEE SENSE
VUV
VDRAIN
+
VS +48V
-
VSENSE
Figure 1a. Test Circuit 1
PWRGD/PWRGD
OV
VDD
DRAIN
MAX5921
MAX5939
GATE
UV
+
VS +48V
-
+
VS +20V
-
10kΩ
0.1µF
10Ω
IRF530
VUV VEE SENSE
Figure 1b. Test Circuit 2
_______________________________________________________________________________________ 5
5 Page 
-48V Hot-Swap Controllers with External
RSENSE and High Gate Pulldown Current
DRAIN
50V/div
GATE - VEE
10V/div
VEE
20V/div
DRAIN
20V/div
1ms/div
INRUSH
CURRENT
5A/div
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.
PWRGD/PWRGD Output
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 VEE.
When the DRAIN voltage of the MAX5921A (see
Selector Guide for complete selection) or MAX5939A is
high with respect to VEE or the GATE voltage is low
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 VDL and the GATE voltage is greater than
∆VGATE - VGH, Q2 turns on and PWRGD pulls low,
enabling the module.
The PWRGD signal can also be used to turn on an LED
ID (Q1)
2A/div
400µs/div
Figure 8. Voltage Step-On Input Supply
or optoisolator to indicate that the power is good (Figure
13) (see the Component Selection Procedure section).
When the DRAIN voltage drops below VDL and the
GATE voltage is greater than ∆VGATE - VGH, MOSFET
Q3 turns on, shorting I1 to VEE and turning Q2 off. The
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 VEE (Figure 12) or the GATE voltage is low
due to an undervoltage condition, the internal MOSFET
Q3 is turned off so that I1 and the internal MOSFET Q2
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 Voltage Regulation
GATE goes high when the following startup conditions
are met: UV is high, OV is low, the supply voltage is
above VUVLOH, and (VSENSE - VEE) is less than 50mV.
The gate is pulled up with a 45µA current source and is
regulated at 13.5V above VEE. The MAX5921/MAX5939
include an internal clamp that ensures the GATE voltage
of the external MOSFET never exceeds 18V. During a
fast-rising VDD, an additional dynamic clamp keeps the
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).
______________________________________________________________________________________ 11
11 Page | ||
| Páginas | Total 18 Páginas | |
| PDF Descargar | [ Datasheet MAX5939.PDF ] | |
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