Datasheet
Micrel, Inc. MIC20xx Family
August 2011
23
M9999-080211-D
Application Information
Setting I
LIMIT
The MIC2009/2019’s current limit is user programmable
and controlled by a resistor connected between the
I
LIMIT
pin and GND. The value of this resistor is
determined by the following equation:
SET
LIMIT
R
LF)itFactor(CCurrentLim
I =
or
(A)I
LF)itFactor(CCurrentLim
R
LIMIT
SET
=
For example: Set I
LIMIT
= 1.25A
Looking in the Electrical specifications we will find CLF
at I
LIMIT
= 1A.
Min Typ Max Units
190 243 293 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 243V. Applying the
equation above:
Ω==Ω 4.194
1.25A
243V
)(R
SET
R
SET
= 196
(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 we used the typical
value of CLF to calculate R
SET
. We can determine
I
LIMIT
’s spread by using the minimum and maximum
values of CLF and the calculated value of R
SET
.
A97.0
196
190V
I
LIMIT_MIN
=
Ω
=
1.5A
196
293V
I
LIMIT_MAX
==
Giving us a maximum I
LIMIT
variation over temperature
of:
I
LIMIT_MIN
I
LIMIT_TYP
I
LIMIT_MAX
0.97A (-22%) 1.25A 1.5A (+20%)
I
OUT
R
SET
I
LIMIT_MIN
I
LIMIT_MAX
0.1A 1928 0.063A 0.136A
0.2A 993 0.137A 0.265A
0.3A 673 0.216A 0.391A
0.4A 511 0.296A 0.515A
0.5A 413 0.379A 0.637A
0.6A 346 0.463A 0.759A
0.7A 299 0.548A 0.880A
0.8A 263 0.634A 1.001A
0.9A 235 0.722A 1.121A
Table 2. MIC20x9A R
SET
Table
I
OUT
R
SET
I
LIMIT_MIN
I
LIMIT_MAX
0.2A 1125 0.127A 0.267A
0.3A 765 0.202A 0.390A
0.4A 582 0.281A 0.510A
0.5A 470 0.361A 0.629A
0.6A 395 0.443A 0.746A
0.7A 341 0.526A 0.861A
0.8A 300 0.610A 0.976A
0.9A 268 0.695A 1.089A
1A 243 0.781A 1.202A
1.1A 222 0.868A 1.314A
1.2A 204 0.956A 1.426A
1.3A 189 1.044A 1.537A
1.4A 176 1.133A 1.647A
1.5A 165 1.222A 1.757A
Table 3. MIC20x9 R
SET
Table