Linear Technology LTC4361-1/LTC4361-2 Overvoltage/Overcurrent Protection Controller with Latchoff/Auto-Retry DC1506A DC1506A 데이터 시트
제품 코드
DC1506A
LTC4361-1/LTC4361-2
7
436112fb
The typical LTC4361 application protects 2.5V to 5.5V
systems in portable devices from power supply overvolt-
age. The basic application circuit is shown in Figure 1.
Device operation and external component selection is
discussed in detail in the following sections.
applicaTions inFormaTion
Figure 1. Protection from Input Overvoltage and Overcurrent
GATE
M1
Si1470DH
R
SENSE
0.025Ω
SENSE
IN
436112 F01
V
OUT
5V
1.5A
V
IN
5V
LTC4361
OUT
PWRGD
ON
GND
C
OUT
10µF
The GATE ramp rate is limited to 3V/ms. V
OUT
follows at
a similar rate which results in an inrush current into the
load capacitor C
OUT
of:
I
INRUSH
= C
OUT
•
dV
GATE
dt
= C
OUT
• 3 mA/µF
[
]
The servo loop is compensated by the parasitic capaci-
tance of the external MOSFET. No further compensation
components are normally required. In the case where
the parasitic capacitance is less than 100pF, a 100pF
compensation capacitor between GATE and ground may
be required.
An even slower GATE ramp and lower inrush current can
An even slower GATE ramp and lower inrush current can
be achieved by connecting an external capacitor, C
G
, from
GATE to ground. The voltage at GATE then ramps up with a
slope equal to 10µA/C
G
[V/s]. Choose C
G
using the formula:
C
G
=
10µA
I
INRUSH
• C
OUT
Overvoltage
When power is first applied, V
When power is first applied, V
IN
must remain below 5.7V
(V
IN(OV)
–
∆V
OV
) for more than 130ms before GATE is
ramped up to turn on the MOSFET. If V
IN
then rises above
5.8V (V
IN(OV)
), the overvoltage comparator activates the
30mA fast pull-down on GATE within 1µs. After an over-
voltage condition, the MOSFET is held off until V
IN
once
again remains below 5.7V for 130ms.
Overcurrent
The overcurrent comparator protects the MOSFET from
The overcurrent comparator protects the MOSFET from
excessive current. It trips when the SENSE pin falls more
than 50mV below IN for 10µs. When the overcurrent
comparator trips, GATE is pulled low quickly and the
PWRGD pull-down releases. The LTC4361-2 automatically
tries to apply power again after a 130ms start-up delay.
Start-Up
When V
When V
IN
is less than the undervoltage lockout level of
2.1V, the GATE driver is held low and the PWRGD pull-down
is high impedance. When V
IN
rises above 2.1V and ON is
held low, a 130ms delay cycle starts. Any undervoltage or
overvoltage event at IN (V
IN
< 2.1V or V
IN
> 5.7V) restarts
the delay cycle. This delay allows the N-channel MOSFET
to isolate the output from any input transients that occur
at start-up. When the delay cycle completes, GATE starts
its slow ramp-up.
GATE Control
An internal charge pump provides a gate overdrive greater
An internal charge pump provides a gate overdrive greater
than 3.5V when 2.5V ≤ V
IN
< 3V. If V
IN
≥ 3V, the gate drive
is guaranteed to be greater than 4.5V. This allows the use
of logic-level N-channel MOSFETs. An internal 6V clamp
between GATE and OUT protects the MOSFET gate.