DC1575A Linear Technology, DC1575A Datasheet - Page 7

• Manufacturer Part Number: DC1575A
• Description: LTC4362-1/LTC4362-2 Overvoltage/Overcurrent Protector With LatchOff/Auto-Retry
• Manufacturer: Linear Technology
• Series: -r

Specifications of DC1575A

• Design Resources: DC1575A Schematic DC1575 Design Files
• Main Purpose: Overvoltage/Overcurrent Protection
• Embedded: No
• Utilized Ic / Part: LTC4362-2
• Primary Attributes: -
• Secondary Attributes: -
• Kit Application Type: Power Management
• Application Sub Type: Overvoltage Protection
• Features: Demonstrates Two Protection Schemes Selected At JP2, Provides Connection For USB Protection
• Lead Free Status / Rohs Status: Not applicable / Not applicable

OPERATION
If the voltage at the IN pin exceeds 5.8V (V
internal N-channel MOSFET is turned off quickly to protect
the load. The incoming power supply must remain below
5.7V (V
delay to restart the OUT ramp-up.
An internal sense resistor is used to implement an
overcurrent protection with a 1.5A current trip thresh-
old and a 10μs glitch fi lter. After an overcurrent, the
LTC4362-1 latches off while the LTC4362-2 restarts fol-
lowing a 130ms delay.
Start-Up
When V
2.1V, the internal N-channel MOSFET is held off and the
PWRGD pull-down is high impedance. When V
above 2.1V and ON is held low, a 130ms delay cycle
starts. Any undervoltage or overvoltage event at IN (V
< 2.1V or V
allows the MOSFET to isolate the output from any input
transients that occur at start-up. When the delay cycle
completes, the MOSFET is turned on and OUT starts its
slow ramp-up.
APPLICATIONS INFORMATION
The typical LTC4362 application protects 2.5V to 5.5V sys-
tems in portable devices from power supply overvoltage.
The basic application circuit is shown in Figure 1. Device
operation and external component selection is discussed
in detail in the following sections.
Figure 1. Protection from Overvoltage and Overcurrent
OUT(OV)
IN
V
5V
IN
is less than the undervoltage lockout level of
IN
> 5.7V) restarts the delay cycle. This delay
– ΔV
IN
ON
LTC4362
GND
OV
PWRGD
) for the duration of the start-up
OUT
436212 F01
V
5V
IO
R1
1k
D1
LN1351CTR
C
10μF
OUT
V
5V
0.5A
OUT
IN(OV)
IN
), the
rises
IN
The LTC4362 has a CMOS compatible ON input. When
driven low, the part is enabled. When driven high, the
internal N-channel MOSFET is turned off and the sup-
ply current of the LTC4362 drops to 1.5μA. The PWRGD
pull-down releases during this low current sleep mode,
UVLO, overvoltage, overcurrent or thermal shutdown and
the subsequent 130ms start-up delay. After the start-up
delay, the internal MOSFET gate starts its 3V/ms ramp-up.
It trips an internal gate high threshold to trigger a 65ms
delay. When that completes, PWRGD pulls low. The output
pull-down device is capable of sinking up to 3mA allow-
ing it to drive an optional LED. The LTC4362 has a GATEP
pin that drives an optional external P-channel MOSFET to
provide protection against negative voltages at IN.
OUT Control
An internal charge pump enhances the internal N-channel
MOSFET with the OUT ramp-rate limited to 3V/ms. This re-
sults in an inrush current into the load capacitor C
Overvoltage
When power is fi rst applied, V
(V
is turned on. If V
overvoltage comparator turns off the internal MOSFET
within 1μs. After an overvoltage condition, the MOSFET is
held off until V
Overcurrent
The overcurrent comparator protects the internal MOSFET
from excessive current. It trips when I
10μs. When the overcurrent comparator trips, the internal
MOSFET is turned off quickly and the PWRGD pull-down
releases. The LTC4362-2 automatically tries to apply power
again after a 130ms start-up delay. The LTC4362-1 has an
internal latch that maintains this off state until it is reset.
To reset this latch, cycle IN below 2.1V (V
IN(OV)
I
INRUSH
– ΔV
= C
LTC4362-1/LTC4362-2
OV
IN
OUT
) for more than 130ms before the output
once again remains below 5.7V for 130ms.
IN
•
then rises above 5.8V (V
dV
dt
OUT
= C
IN
OUT
must remain below 5.7V
• 3 mA/μF
[
OUT
IN(UVL)
IN(OV)
> 1.5A for
]
) or ON
OUT
), the
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of: