MP5092 – DUAL 5.5V, 7.5A LOW RDSON LOAD SWITCH WITH OUTPUT DISCHARGE FUNCTION
MP5092 Rev. 1.0 www.MonolithicPower.com 12
1/8/2015 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2015 MPS. All Rights Reserved.
OPERATION
The MP5092 is designed to limit the in-rush
current to the load when a circuit card is
inserted into a live backplane power source;
thereby limiting the backplane’s voltage drop
and the slew rate of the voltage to the load.
MP5092 integrated two independent load
switches. Any one channel can work alone.
Each channel can provide 7.5A load capability.
It provides an integrated solution to monitor
output current to eliminate the need for an
external current power MOSFET, and current
sense device.
Enable
When input voltage is greater than the under-
voltage lockout threshold (UVLO), typically 0.5V,
MP5092 can be enabled by pulling EN pin to
higher than 1.5V. Pulling down to ground will
disable MP5092.
The recommend start up sequence is power up
V
IN
first. After V
IN
is ready, pull EN voltage to
high.
Current Limit
The MP5092 provides a constant current limit
that can be programmed by an external resistor.
Once the device reaches its current limit
threshold, the internal circuit regulates the gate
voltage to hold the current in the power FET
constant. The typical response time is about
20µs and the output current may have a small
overshoot during this time period.
The pre-set current limit value can be
calculated by below equation:
)(
82000
)(
Ω
=
LIM
LIM
R
AI
(1)
R
LIM
is R1 and R2 which are placed between
ILIM1/2 pin to ground in Figure 4.
If the current limit block starts to regulate the
output current, the power loss on power
MOSFET will cause the IC temperature rise. If
the junction temperature rose to high enough, it
will trigger thermal shutdown. After thermal
shutdown happened, it will disable the output
until the over temperature fault remove. The
over temperature threshold is 155
o
C and
hysteresis is 30
o
C.Bias Vcc Supply
Vcc is the bias supply for internal analog circuit.
It is better to have a decouple capacitor to filter
the noise. If the main power voltage V
IN
is
higher than 3V, the Vcc can be directly
connected to V
IN
.
Short-Circuit Protection
If the load current increases rapidly due to a
short circuit, the current may exceed the current
limit threshold by a lot before the control loop
can respond. If the current reaches an internal
secondary current limit level (about 13A), a fast
turn-off circuit activates to turn off the power
FET. This limits the peak current through the
switch to limit the input voltage drop. The total
short circuit response time is about 200ns. If
fast off works, it will keep off the power FET for
80us. After that time period, it will re-turn on
power FET..
Output Discharge
MP5092 has output discharge function. This
function can discharge the Vo by internal pull
down resistance when IC disabled and the load
is very light.
Soft-Start
A capacitor connected to the SS pin determines
the soft-start time. There is an internal 9uA
constant current source charge SS cap and
ramps up the voltage on the SS pin. The output
voltage rises at 3 times the slew rate to the SS
voltage.
The soft-start time can be calculated by below
equation:
)(
)()(
3
1
)(
uAI
nFCVV
msT
SS
SSOUT
SS
⋅
×=
(2)
T
SS
is the soft-start time, I
SS
is internal 9uA
constant current, C
SS
is external soft-start cap.
The suggestion minimum SS cap should be
bigger than 4.7nF. If the SS pin is floated or SS
cap is too small, the Vo rising time will be just
limited by power MOS charge time.
