参数资料
型号: MAX5932ESA+T
厂商: Maxim Integrated
文件页数: 10/15页
文件大小: 247K
描述: IC HOT-SWAP CONTROLLER 8-SOIC
产品培训模块: Lead (SnPb) Finish for COTS
Obsolescence Mitigation Program
标准包装: 2,500
类型: 热交换控制器
应用: 通用
内部开关:
电源电压: 9 V ~ 80 V
工作温度: -40°C ~ 85°C
安装类型: 表面贴装
封装/外壳: 8-SOIC(0.154",3.90mm 宽)
供应商设备封装: 8-SOIC
包装: 带卷 (TR)
Positive High-Voltage, Hot-Swap Controller
10   ______________________________________________________________________________________
Applications Information
Hot-Circuit Insertion
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.
Power-Up Sequence
The power supply on a board is controlled by placing
an external n-channel MOSFET (Q1) in the power path
(Figure 5). Resistor R
SENSE
provides current detection
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
CC
exceeds the under-
voltage lockout threshold, and the voltage on TIMER is
less than 1.233V, transistor Q1 turns on (Figure 6).
The voltage at GATE rises with a slope equal to
10礎/C1 and the supply inrush current is set at:
I
INRUSH
= C
L
x 10礎/C1
When the voltage across the current-sense resistor
R
SENSE
reaches V
SENSETRIP
, then the inrush current is
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.
Short-Circuit Protection
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
CC
(pin 8) and SENSE (pin 7).
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 (Figure 7).
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:
I
LIMIT
= 47mV/R
SENSE
For a 0.025& 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 Q1s drain
current depends on:
"   Q1s input capacitance.
"   GATE capacitor C1 and compensation resistor R6.
"   The internal delay from SENSE to GATE.
Figure 8 shows the delay from a voltage step at SENSE
until GATE voltage starts falling, as a function of
overdrive.
POWER-UP WAVEFORMS
I
SENSE
2A/div
PWRGD
50V/div
OUTPUT
50V/div
GATE
50V/div
20ms/div
Figure 6. Power-Up Waveforms
V
CC
 - V
SENSE
V
FB
12mV
47mV
0.5V
0V
Figure 7. Current-Limit Sense Voltage vs. Feedback Voltage
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