Datasheet

Applications Information
Setting ON, OFF, and OV Voltage Levels
The trip levels for ON, OFF, and OV can readily be set
with a 4-element resistor-divider. Total resistance is a
trade off of quiescent current, threshold tolerance due
to pin input bias current (25nA), and the ability to follow
very fast supply transients. Both ON and OV have hys-
teresis on the reference threshold voltage: the rising
reference threshold is 1.25V and the falling threshold is
1.125V. The reference threshold voltage for OFF is
1.25V. In determining a set of resistors, use V
REF
=
1.25V for ON, OFF, and OV and an R
TOT
= 100kΩ in
this example. See Figure 12 for nomenclature. For this
example, use V
OV
= 80V, V
ON
= 42V, and V
OFF
= 38V
as the desired voltage trip levels.
1) R
4
= R
TOT
x V
REF
/ V
OV
2) R
3
= R
TOT
x V
REF
/ V
ON
- R
4
3) R
2
= R
TOT
x V
REF
/ V
OFF
- R
3
- R
4
4) R
1
= R
TOT
- R
2
- R
3
- R
4
The exact result to three decimal places is R1 =
96.711kΩ, R2 = 313Ω, R3 = 1.414kΩ, and R4 =
1.563kΩ. When converted to the nearest 1% standard
resistor, the values become R1 = 97.6kΩ, R2 = 316Ω,
R3 = 1.40kΩ, and R4 = 1.58kΩ.
MAX5938
-48V Hot-Swap Controller with V
IN
Step Immunity,
No R
SENSE
, and Overvoltage Protection
14 ______________________________________________________________________________________
Figure 12. Programming the MAX5938’s ON, OFF, and OV
Thresholds
MAX5938
GND
OFF
ON
V
IN
= (GND - V
EE
)
R4
R3
R2
R1
OV
V
EE
Figure 13. MAX5938 Circuit-Breaker Threshold Adjustment
MAX5938
C
LOAD
LOAD
SC TRIP
R
ON
V
OUT
I
LOAD
CB TRIP
t
CB_DLY
R
INT
2kΩ
±0.5%
R
CB_ADJ
R
R
V
SC
V
EE
GND
50µA
CB_ADJ
I
CB_ADJ