LT4254IGN#TRPBF Linear Technology, LT4254IGN#TRPBF Datasheet - Page 10

• Manufacturer Part Number: LT4254IGN#TRPBF
• Description: IC CTLR HOTSWAP POS 16-SSOP
• Manufacturer: Linear Technology
• Type: Hot-Swap Controllerr

Specifications of LT4254IGN#TRPBF

• Applications: General Purpose
• Internal Switch(s): No
• Voltage - Supply: 10.8 V ~ 36 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-SSOP (0.150", 3.90mm Width)
• Family Name: LT4254
• Package Type: SSOP N
• Operating Supply Voltage (min): 10.8V
• Operating Supply Voltage (max): 36V
• Operating Temperature (min): -40C
• Operating Temperature (max): 85C
• Operating Temperature Classification: Industrial
• Product Depth (mm): 3.99mm
• Product Height (mm): 1.5mm
• Mounting: Surface Mount
• Pin Count: 16
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

APPLICATIO S I FOR ATIO
LT4254
Resistor R7 compensates the current control loop while
R6 prevents high frequency oscillations in Q1.
When the power pins first make contact, transistor Q1 is
held off. If the voltage on the V
externally programmed undervoltage and overvoltage
thresholds, and the voltage on the TIMER pin is less than
4.65V (typ), transistor Q1 will be turned on (Figure 6). The
voltage at the GATE pin rises with a slope equal to 35µA/
C1 and the supply inrush current is set at:
If the voltage across the current sense resistor R5 reaches
V
internal current limit circuitry. The voltage on the GATE pin
is adjusted to maintain a constant voltage across the sense
resistor and the TIMER pin begins to charge.
When the FB pin voltage goes above the low-to-high V
threshold, the PWRGD pin goes high.
Short-Circuit Protection
The LT4254 features a programmable foldback current
limit with an electronic circuit breaker that protects against
short circuits or excessive load currents. The current limit
is set by placing a sense resistor (R5) between V
SENSE.
To limit excessive power dissipation in the pass transistor
and to reduce voltage spikes on the input supply during
short-circuit conditions at the output, the current folds
10
SENSETRIP
I
INRUSH
= C
, the inrush current will be limited by the
L
• 35µA/C1
U
GND
24V
V
IN
U
0.1µF
(SHORT PIN)
C3
CC
W
pin is between the
R1
324k
R2
40.2k
R3
40.2k
C2
33nF
1
2
4
9
UV
OV
OPEN
TIMER
Figure 5. 2A, 24V Application
U
V
CC
16
0.025Ω
LT4254
CC
GND
R5
8
SENSE
PWRGD
and
RETRY
GATE
FB
15
FB
13
10
7
5
back as a function of the output voltage, which is sensed
internally on the FB pin.
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 at the FB pin
increases, the voltage across the sense resistor increases
until the FB pin reaches 2V, at which point the voltage
across the sense resistor is held constant at 50mV (see
Figure 7). The current limit threshold is calculated as:
where R5 is the sense resistor.
For a 0.025Ω sense resistor, the current limit is set at
2000mA and folds back to 600mA when the output is
shorted to ground. Thus, MOSFET dissipation under short-
circuit conditions is reduced from 36W to12W. See the
IRF530
Q1
500mA/DIV
UV = 20V
OV = 40V
PWRGD = 18V
I
LIMIT
R6
10Ω
R7
100Ω
20V/DIV
20V/DIV
PWRGD
20V/DIV
C1
10nF
GATE
V
I
OUT
OUT
= 50mV/R5
D1
CMPZ5241B
11V
Figure 6. Start-Up Waveforms
R8
140k
R9
40.2k
4254 F05
R4
27k
2.5ms/DIV
PWRGD
C
L
V
24V
1.5A
OUT
C
L
= 185µF
4254 F06
4254fb