參數(shù)資料
型號: LT1641IS8#TR
廠商: Linear Technology
文件頁數(shù): 9/12頁
文件大小: 192K
描述: IC CTRLR HOTSWAP POS VOLT 8SOIC
標準包裝: 2,500
類型: 熱交換控制器
應(yīng)用: 通用
內(nèi)部開關(guān):
電源電壓: 9 V ~ 80 V
工作溫度: -40°C ~ 85°C
安裝類型: 表面貼裝
封裝/外殼: 8-SOIC(0.154",3.90mm 寬)
供應(yīng)商設(shè)備封裝: 8-SOIC
包裝: 帶卷 (TR)
9
LT1641
1641fd
APPLICATIO  S I FOR  ATIO
U
U
U
Automatic Restart
To force the LT1641 to automatically restart after an
overcurrent fault, the bottom plate of capacitor C1 can be
tied back to the ON pin (Figure 10).
When an overcurrent condition occurs, the GATE pin is
driven to maintain a constant voltage across the sense
resistor. The capacitor C2 at the TIMER pin will begin to
charge. When the voltage at the TIMER pin reaches
1.233V, the GATE pin is immediately pulled to GND and
transistor Q1 turns off. Capacitor C1 momentarily pulses
the ON pin low and allows the part to turn off. When the
voltage at the TIMER pin ramps back down to 0.5V, the
LT1641 turns on again. If the short-circuit condition at the
output still exists, the cycle will repeat itself indefinitely
with a 3.75% on-time duty cycle which prevents Q1 from
overheating. The waveforms are shown in Figure 11.
Undervoltage and Overvoltage Detection
The ON pin can be used to detect an undervoltage condi-
tion at the power supply input. The ON pin is internally
connected to an analog comparator with 80mV of hyster-
esis. If the ON pin falls below its threshold voltage (1.233V),
the GATE pin is pulled low and is held low until ON is high
again.
Figure 12 shows an overvoltage detection circuit. When
the input voltage exceeds the Zener diodes breakdown
voltage, D2 turns on and starts to pull the TIMER pin high.
After the TIMER pin is pulled higher than 1.233V, the fault
latch is set and the GATE pin is pulled to GND immediately,
Figure 8. Response Time to Overcurrent
12mV
0V
0.5V
V
FB
1641 F07
47mV
V
CC
  V
SENSE
Figure 7. Current Limit Sense Voltage vs Feedback Pin Voltage
50mV
100mV
150mV
200mV
1641 F08
12祍
10祍
8祍
6祍
4祍
2祍
RESPONSE TIME
V
CC
  V
SENSE
turning off transistor Q1. The waveforms are shown in
Figure 13. Operation is restored either by interrupting
power or by pulsing ON low.
Power Good Detection
The LT1641 includes a comparator for monitoring the
output voltage. The noninverting input (FB pin) is com-
pared against an internal 1.233V precision reference and
exhibits 80mV hysteresis. The comparators output
(PWRGD pin) is an open collector capable of operating
from a pull-up as high as 100V.
The PWRGD pin can be used to directly enable/disable a
power module with an active high enable input. Figure 14
shows how to use the PWRGD pin to control an active low
enable input power module. Signal inversion is accom-
plished by transistor Q2 and R7.
Supply Transient Protection
The LT1641 is 100% tested and guaranteed to be safe
from damage with supply voltages up to 100V. However,
spikes above 100V may damage the part. During a short-
circuit condition, the large change in currents flowing
through the power supply traces can cause inductive
voltage spikes which could exceed 100V. To minimize the
spikes, the power trace parasitic inductance should be
minimized by using wider traces or heavier trace plating
and a surge suppressor placed between V
CC
 and GND.
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