MAX4373/MAX4374/MAX4375
Low-Cost, Micropower, High-Side Current-Sense
Amplifier + Comparator + Reference ICs
10 ______________________________________________________________________________________
Internal Comparator(s)
The MAX4373/MAX4374/MAX4375 contain an open-
drain output comparator for current limiting. The com-
parator’s negative terminal is connected to the internal
600mV reference. The positive terminal is accessible at
CIN1. When RESET is high, the internal latch is active,
and once CIN1 rises above 600mV, the output latches
into the open state. Pulsing RESET low for 1.5µs resets
the latch, and holding RESET low makes the latch
transparent. See
RESET at Power-Up
section
The MAX4374/MAX4375 contain an additional open-
drain comparator. The negative terminal of the
MAX4374’s additional comparator and the positive ter-
minal of the MAX4375’s additional comparator are con-
nected to the internal 600mV reference as shown in
Figure 1. The positive terminal of the MAX4374’s addi-
tional comparator and the negative terminal of the
MAX4375’s additional comparator are accessible at
CIN2.
___________Applications Information
Recommended Component Values
Ideally, the maximum load current will develop the full-
scale sense voltage across the current-sense resistor.
Choose the gain version needed to yield the maximum
output voltage required for the application:
where V
SENSE
is the full-scale sense voltage, 150mV for
gains of +20V/V and +50V/V or 100mV for a gain of
+100V/V. A
V
is the gain of the device. The minimum
supply voltage is V
OUT
+ 0.25V. Note that the output for
the gain of +100V/V is internally clamped at 12V.
Calculate the maximum value for R
SENSE
so that the
differential voltage across RS+ and RS- does not
exceed the full-scale sense voltage:
Choose the highest value resistance possible to maxi-
mize V
SENSE
and thus minimize total output error.
In applications monitoring high current, ensure that
R
SENSE
is able to dissipate its own I
2
R loss. If the resis-
tor’s power dissipation is exceeded, its value may drift
or it may fail altogether, causing a differential voltage
across the terminals in excess of the absolute maxi-
mum ratings. Use resistors specified for current-sens-
ing applications.
Overcurrent Protection Circuit
The overcurrent protection circuit, shown in Figure 2,
uses the MAX4373 to control an external P-channel
MOSFET. The MOSFET controlled by the MAX4373
opens the current path under overload conditions. The
latched output of the MAX4373’s comparator prevents
the circuit from oscillating, and the pushbutton resets
the current path after an overcurrent condition.
Window Detection Circuit
Figure 3 shows a simple circuit suitable for window
detection. Let I
OVER
be the minimum load current
(I
LOAD
) required to cause a low state at COUT2, and let
I
UNDER
be the maximum load current required to cause
a high state at COUT1:
where A
V
is the gain of the device and V
REF
is the inter-
nal reference voltage (0.6V typ).
Connect COUT1 and COUT2; the resulting comparator
output will be high when the current is inside the cur-
rent window and low when the current is outside the
window. The window is defined as load currents less
than I
OVER
and greater than I
UNDER
.
