LT1641CS8#TRPBF Linear Technology, LT1641CS8#TRPBF Datasheet - Page 8

• 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

LT1641
APPLICATIO S I FOR ATIO
To prevent excessive power dissipation in the pass tran-
sistor 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, which is
sensed at the FB pin (Figure 7).
When the voltage at the FB pin is 0V, the current limit
circuit drives the GATE pin to force a constant 12mV drop
across the sense resistor. As the output voltage at the FB
pin increases, the voltage across the sense resistor in-
creases until the FB pin reaches 0.5V, at which point the
voltage across the sense resistor is held constant at 47mV.
The maximum current limit is calculated as:
For a 0.025Ω sense resistor, the current limit is set at
1.88A and folds back to 480mA when the output is shorted
to ground.
The LT1641 also features a variable overcurrent response
time. The time required for the chip to regulate the GATE
pin (Pin 6) voltage is a function of the voltage across the
sense resistor connected between the V
the SENSE pin (Pin 7). The larger the voltage, the faster the
gate will be regulated. Figure 8 shows the response time
as a function of overdrive at the SENSE pin.
8
SHORT
GND
24V
V
I
IN
49.9k
PIN
LIMIT
3.4k
1%
1%
R1
R2
= 47mV/R
1
TIMER
ON
V
CC
0.025Ω
8
5
Figure 5. Typical Application
R
C2
0.68µF
S
SENSE
SENSE
U
7
LT1641
10Ω
5%
R5
IRF530
GATE
GND
Q1
U
6
4
1k, 5%
R6,
PWRGD
10nF
C1
D1
CMPZ
5248B
FB
W
2
3
CC
R3
59k
1%
R4
3.57k
1%
pin (Pin 8) and
R7
24k
5%
U
+
PWRGD
1641 F05
C
L
V
OUT
TIMER
The TIMER pin (Pin 5) provides a method for program-
ming the maximum time the chip is allowed to operate in
current limit. When the current limit circuitry is not active,
the TIMER pin is pulled to GND by a 3µA current source.
After the current limit circuit becomes active, an 80µA pull-
up current source is connected to the TIMER pin and the
voltage will rise with a slope equal to 77µA/C
as the current limit circuit remains active. Once the desired
maximum current limit time is set, the capacitor value is:
C(nF) = 62 • t(ms).
If the current limit circuit turns off, the TIMER pin will be
discharged to GND by the 3µA current source.
Whenever the TIMER pin reaches 1.233V, the GATE pin is
immediately pulled to GND and the TIMER pin is pulled
back to GND by the 3µA current source. The part is not
allowed to turn on again until the voltage at the TIMER pin
falls below 0.5V.
The waveform in Figure 9 shows how the output turns off
following a short-circuit. The drop across the sense resis-
tor is held at 12mV as the timer ramps up. Since the output
did not rise bringing FB above 0.5V, the circuit turns off.
Figure 6. Power-Up Waveforms
TIMER
as long
1641fd