Datasheet

Power-On Reset
The MAX9611/MAX9612 include power-on reset circuitry
that ensures all registers reset to a known state on power-
up. Once V
CC
goes above 2.4V, the POR circuit releases
the registers for normal operation.
Applications Information
Inrush Current Limiter
The MAX9611 can be used as an inrush current limiter
for a number of applications as shown in Figure 3. Note
that the sense resistor can be placed on either side of
the pFET. Since the input common-mode voltage of the
MAX9611 extends to ground, the sense resistor can be
placed at the load side as well, allowing current to be
sensed even when there is a dead-short on the load.
The inrush current limiting circuit reads and measures
the load current during normal operation and can limit
the load current to a user-set value. In normal operation,
the load current is below the set threshold. The pFET is
fully turned on because the op-amp output is at 0V. In the
event of an overcurrent situation at the load, the op-amp
controls the pFET’s gate-voltage so it transitions to a
linear region, thus limiting the load current. In this case,
the op-amp output voltage is between 0V and V
BAT
, as
required for current-limiting.
Choose a suitable sense resistor and a low R
DS-ON
pFET
to ensure the best efficiency during normal operation.
Choose a pFET with large power dissipation to ensure com-
pliance with safe operating area of the pFET. The MAX9611
comes equipped with a variety of watchdog options to help
with this design (see Control Register 2, Table 7).
Choose resistor values R1 and R2 to ensure that the
pFET is fully on in normal operating conditions and to
ensure that the VGS maximum rating is not exceeded.
Also, R1 and R2 help limit the current in the open-drain
output stage of the internal op amp. R
COMP
and C
COMP
help rolloff high-frequency gain of the feedback control
system. R2 and C
COMP
set a pole, for which 10kHz is a
good choice. R
COMP
and C
COMP
set a zero, for which
100kHz is a good choice.
With the internal gain of the current-sense amplifier
(2.5V/V), the inrush current-limit threshold can be set
using resistor-divider R3 and R4 as follows:
( )
( )
CC
LIMIT
SENSE
V R3
I
R4 R3 2.5 R
×
=
+×
Note: The inrush current limiter can be changed to a high-
side relay-disconnect circuit by using the MAX9611 set to
comparator mode (MODE 111).
Figure 3. Inrush Current Limiter
MAX9611
0.1µF
R4R1
R2
C
COMP
V
BAT
R
COMP
R3
0.1
µF
1
µF
V
CC
I
2
C CLOCK
INPUT
I
2
C DATA
INPUT/OUTPUT
RS+ RS-
A0
A1
SCL
SDA
OUT
SET
2.7V TO 5.5V
GND
LOAD
R
SENSE
P
(OUTPUT SET TO OP-AMP MODE)
INRUSH CURRENT LIMITER
MAX9611/MAX9612 High-Side, Current-Sense Ampliers with
12-Bit ADC and Op Amp/Comparator
www.maximintegrated.com
Maxim Integrated │ 17