LT1641CS8#TRPBF Linear Technology, LT1641CS8#TRPBF Datasheet - Page 9

• Manufacturer Part Number: LT1641CS8#TRPBF
• Description: IC CTRLR HOTSWAP POS VOLT 8SOIC
• Manufacturer: Linear Technology
• Type: Hot-Swap Controllerr

Specifications of LT1641CS8#TRPBF

• Applications: General Purpose
• Internal Switch(s): No
• Voltage - Supply: 9 V ~ 80 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (0.154", 3.90mm Width)
• Family Name: LT1641
• Package Type: SOIC N
• Operating Supply Voltage (min): 9V
• Operating Supply Voltage (max): 80V
• Operating Temperature (min): 0C
• Operating Temperature (max): 70C
• Operating Temperature Classification: Commercial
• Product Depth (mm): 3.99mm
• Product Height (mm): 1.5mm
• Product Length (mm): 5mm
• Mounting: Surface Mount
• Pin Count: 8
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

APPLICATIO S I FOR ATIO
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 diode’s 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 7. Current Limit Sense Voltage vs Feedback Pin Voltage
V
CC
– V
SENSE
47mV
12mV
0V
U
U
0.5V
W
1641 F07
V
FB
U
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 comparator’s 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
12µs
10µs
8µs
6µs
4µs
2µs
RESPONSE TIME
Figure 8. Response Time to Overcurrent
50mV
100mV
150mV
200mV
CC
LT1641
and GND.
V
CC
– V
SENSE
1641 F08
1641fd
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