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MAX34406

Quad Current-Sense Amplifier

with Overcurrent Threshold Comparators

Detailed Description

The MAX34406 quad-channel, unidirectional, high-side,

current-sense amplifier features a 2.0V to 28V input

common-mode range. This feature allows the monitoring

of current out of a voltage supply as low as 2.0V. The

device monitors current through a current-sense resistor

and amplifies the voltage across that resistor.

Current-sense amplifier output voltages (OUT1 to OUT4)

exceeds 1.0V, the corresponding overcurrent warning

output (OC1 to OC4) is asserted. If the enable input

(ENA) is logic-high, SHTDN asserts when any of the four

overcurrent outputs go logic-high. Assertion of SHTDN on

overcurrent can be delayed and/or filtered by attaching

an external capacitor to CDLY. Once SHTDN is latched

high impedance, it remains so until ENA is toggled.

The unidirectional current-sense amplifiers used in each

channel of the device have a well established history. For

each channel, an op amp is used to force the current

through an internal gain resistor at IN+, which has a value

of R1, such that its voltage drop equals the voltage drop

internal resistor at IN- with the same value as R1 to mini-

mize offset voltage. The current through R1 is sourced by

a high-voltage p-channel FET. Its source current is the

same as its drain current, which flows through a second

The gain accuracy is based on the matching of the two

for the MAX34406T, 50V/V for the MAX34406F, 100V/V

for the MAX34406H, and 200V/V for the MAX34406W.

The output is protected from input overdrive by use of a

6V clamp-protection circuit.

Applications Information

Choosing the Sense Resistor

lowing sections.

Voltage Loss

to drop due to IR loss. For minimal voltage loss, use the

The device is unique because the supply voltage for

the current-sense amplifier in each channel is the input

common-mode voltage for that channel (the average

voltage at INx+ and INx-). There are no separate supply

voltage pins for the current-sense amplifiers. Therefore,

the OUTx voltage swing for a given channel is limited by

the minimum voltage at IN+ for that channel.

and

OUTx

SENSE

LOAD

V

(MAX)

R

G I

(MAX)

=

×

minimum INx+ voltage. For best performance with a 3.6V

120mV (gain of 25V/V), 60mV (gain of 50V/V), 30mV (gain

of 100V/V), or 15mV (gain of 200V/V) of sense voltage for

the full-scale current in each application. These can be

increased by use of a higher minimum input voltage.

Accuracy

and gain error (GE). For all variants of the device,

MAX34406T/F/H or 0.8% (max) for the MAX34406W. Use

the linear equation to calculate total error:

OS

SENSE

V

Error (%) GE

100

V





=

±×









more accurately because offsets are less significant

when the sense voltage is larger.

Table 1. Internal Gain Setting Resistors

(Typical Values)

GAIN (V/V)

R1 (I)

200

100

20

100

100

10

50

200

10

25

400

10