MIC2544A Datasheet, PDF (15/19 Pages) Micrel Semiconductor – Programmable Current Limit High-Side Switch

Micrel, Inc.
Setting I_LIMIT
The MIC2544A/2548A’s current limit is user
programmable and controlled by a resistor connected
between the I_LIMIT pin and ground. The value of this
resistor is determined by the following equation:
I _LIMIT
= ^{CurrentLimitFactor(CLF)}
R_SET
or
R _SET
=
CurrentLimitFactor(V)
I_LIMIT (A)
For example: Set I_LIMIT = 1.0A
Looking in the Electrical specifications we will find CLF
at I_LIMIT = 1 A.
Min
Typ
184
230
Max
Units
276
V
Table 1. CLF at I_LIMIT = 1A
For the sake of this example, we will say the typical
value of CLF at an I_OUT of 1A is 230V. Applying the
equation above:
R_SET (Ω) =
230V
1.0A
= 230Ω
R_SET = 232Ω
(the closest standard 1% value)
Designers should be aware that variations in the
measured I_LIMIT for a given R_SET resistor, will occur
because of small differences between individual ICs
(inherent in silicon processing) resulting in a spread of
I_LIMIT values. In the example above a typical value of CLF
was used to calculate R_SET. One can determine I_LIMIT’s
spread by using the minimum and maximum values of
CLF and the calculated value of R_SET.
I_{LIMIT_MIN}
=
184V
232Ω
=
0.79A
I_{LIMIT _ MAX}
=
276V
232Ω
= 1.19A
MIC2544A/2548A
Giving one a maximum I_LIMIT variation over-temperature
of:
I_{LIMIT_MIN}
0.79A (-21%)
I_{LIMIT_TYP}
1.0A
I_{LIMIT_MAX}
1.19A (+19%)
I_OUT
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
1.2
1.3
1.4
1.5
R_SET
1150
767
575
460
383
329
288
256
230
209
192
177
164
153
I_OUT_Min
0.140
0.210
0.280
0.350
0.480
0.560
0.640
0.720
0.800
0.880
0.960
1.040
1.120
1.200
I_OUT_Max
0.260
0.390
0.520
0.650
0.720
0.840
0.960
1.080
1.200
1.320
1.440
1.560
1.680
1.800
Table 2. MIC2544A/2548A R_SET Table
Short-Circuit Protection
In the event of a short circuit, the output current will fold
back to approximately 70% of the short-circuit current-
limit.
Fault Flag
FLG is an N-channel, open-drain MOSFET output. The
fault flag is active (low) for current-limit or thermal
shutdown conditions. The flag output MOSFET is
capable of sinking a 10mA load to typically 100mV
above ground. The FLG response delay time t_D is
typically 5µs.
April 2010
15
M9999-043010