MAX4373/MAX4374/MAX4375

Low-Cost, Micropower, High-Side

Current-Sense Amplifier +

Comparator + Reference ICs

Maxim Integrated | 11

www.maximintegrated.com

Power-Supply Bypassing

It is recommended that VCC 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 VCC. The simplest

solution is to run VCC from a better regulated supply

(+5V for example), since VCC and RS+ (or RS-) do not

have to be connected together.

For high-speed VCC transients, another solution is to

add a resistor in series with the VCC 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 VCC. 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 VCC 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 VCC, RESET and

GND (see Figure 2). Note that

RESET cannot exceed

VCC + 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 VCC 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

RS-

RS+

OUT

CIN1

CIN2

LOAD

VCC = 2.7V TO 28V

VIN = 0 TO 28V

MAX4375

GND

VCC

GND

R5

R4

RSENSE

+ VSENSE -

R3

COUT1

R2

R1

COUT2

ILOAD

RESET

VPULL-UP

(UP TO 5V)

Figure 3. MAX4375 Window Detector