SGM2523
Programmable Current Limit Switch
DETAILED DESCRIPTION (continued)
Overload Protection
Once an overload occurs, the internal current limit
amplifier limits the output current to the predetermined
value by increasing the on-resistance of the power
switch.
1μA
SS
CSS
CINT
nSWEN
GND
During current limit regulation, the output voltage drops,
resulting in increased power consumption. The
SGM2523 allows ILIM pin floating operation. If ILIM pin
is floating, the current limit will be set as fixed 0.2A
internally.
SGM2523
Figure 7. Output Ramp Time is Set by CSS
Equation 2 shows how to calculate the total output
ramp time (tSS) when the output rises from 0V to VIN:
When the over-current limit condition lasts more than
2ms, the SGM2523A enters the hiccup mode with 2ms
on time and 700ms off time, whereas the SGM2523B
enters shutdown mode.
tSS = 16.1 × 104 × VIN × CSS
(2)
where CSS is in F.
Short-Circuit Protection
A transient short-circuit occurs, due to the limited
bandwidth of the current limit amplifier, which cannot
respond quickly to this event. The SGM2523 contains a
Inrush current can be calculated by the following
formula.
V
IN
I
= COUT
×
(3)
INRUSH
tSS
fast-trip comparator with a threshold (IFAST-TRIP). If IOUT
>
I
FAST-TRIP, the comparator turns off the N-MOSFET and
Rise time can be calculated by multiplying the input
voltage by the slew rate. If floating this pin, the slew
rate of the output obtains a default value ~50V/ms
(minimum tSS).
terminates the short-circuit peak current across the
N-MOSFET rapidly. The fast-trip threshold is 2 times
the overload current limit. The fast-trip comparator can
terminate the transient short-circuit peak current, and
then the current limit function limits the output current to
Overload and Short-Circuit Protections
The device limits current to the output in case of output
shorts and overloads. If an event occurs, device goes
into current limit action, and the value of the current
limit (ILIMIT) is set by RILIM resistor:
ILIMIT
.
IFAST-TRIP = 2 × ILIMIT
(6)
where:
IFAST-TRIP is the fast-trip current limit threshold, which is
measured in A.
I
LIMIT = 10.5 × 10-3 × RILIM
ILIMIT
(4)
(5)
RILIM
=
After the fast-trip is triggered, the fast-trip circuit will first
make the FET turn off for several microseconds, and
then the device enters the current limit start-up period,
where the output current is limited to ILIMIT. After this
period, the behavior of the device is the same as that of
over-current.
10.5×10−3
where:
LIMIT is overload current limit in A.
ILIM is the current limit programming resistor in kΩ.
I
R
In addition to the general over-current protection, the
SGM2523 also integrates fast-trip over-current
protection with quicker response time.
IFAST-TRIP
IFAST-TRIP = 2 × ILIMIT
ILIMIT
Figure 8. Over-Current Protection Levels
SG Micro Corp
www.sg-micro.com
JANUARY 2023
10
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