Datasheet

Power-Supply Bypassing
It is recommended that V
CC
be bypassed to GND with
at least a 0.1µF ceramic capacitor to isolate the IC from
supply voltage transients. It is possible that plugging
in/out a battery or AC adapter/charger could cause
large, fast line transients (>5V/µs) at V
CC
. The simplest
solution is to run V
CC
from a better regulated supply
(+5V for example), since V
CC
and RS+ (or RS-) do not
have to be connected together.
For high-speed V
CC
transients, another solution is to
add a resistor in series with the V
CC
pin and a 0.1µF
capacitor to create an RC time constant to slow the rise
time of the transient. Since these current-sense ampli-
fiers consume less than 100µA, even a 2.5kΩ resistor
only drops an extra 250mV at V
CC
. For most applica-
tions with fast transients, 1kΩ in conjunction with a
0.1µF bypass capacitor works well.
RESET at Power-Up
The RESET pin is used to control the latch function of
comparator 1. Holding RESET low (<0.8V) makes the
latch transparent and COUT1 will respond to changes
at CIN1, above and below the internal 600mV reference
threshold voltage. When RESET is high (>2.0V), once
CIN1 rises above 600mV, COUT1 latches into the
open-drain OFF state and remains in this state even if
CIN1 drops below 600mV. Pulsing RESET low for at
least 1.5µs resets the latch.
There is no internal circuitry to control the reset function
during power-up. To prevent false latching, RESET
must be held low until the V
CC
power has risen above
the 2.7V minimum operating supply voltage. This is
easily accomplished when RESET is driven under µC or
logic gate control. However, if RESET is to be always
connected high, add an RC between V
CC
, RESET and
GND (see Figure 2). Note that RESET cannot exceed
V
CC
+ 0.3V or +12V, whichever is less.
The following formula can be used to determine the
appropriate RC value.
where T is the maximum time for V
CC
to reach 2.7V and
0.8V is the maximum RESET logic low voltage. For
example, a 470kΩ resistor and 0.22µF capacitor will
keep RESET low during a power-up time of up to 36ms.
A faster power-up time is also safe with the calculated
R and C since the capacitor will have even less time to
charge.
RC
T
VV V
T
=
−
()
=
ln . /( . . ) .2 7 2 7 0 8 0 3514
MAX4373/MAX4374/MAX4375
Low-Cost, Micropower, High-Side Current-Sense
Amplifier + Comparator + Reference ICs
______________________________________________________________________________________ 11
RS-RS+
OUT
CIN1
CIN2
LOAD
V
CC
= 2.7V TO 28V
V
IN
= 0 TO 28V
MAX4375
GND
V
CC
GND
R5
R4
R
SENSE
+ V
SENSE
-
R3
COUT1
R2
R1
COUT2
I
LOAD
RESET
V
PULL-UP
(UP TO 5V)
Figure 3. MAX4375 Window Detector