MAX9938T データシートの表示（PDF） - Maxim Integrated

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MAX9938T

1µA, 4-Bump UCSP/SOT23, Precision Current-Sense Amplifier

Maxim Integrated 

1µA, 4-Bump UCSP/SOT23,

Precision Current-Sense Amplifier

Typical Operating Circuit

VBATT = 1.6V TO 28V

ILOAD

RSENSE

RS+

RS-

R1

R1

VDD = 3.3V

LOAD

P

ROUT 10kΩ

GND

MAX9938

OUT

μC

ADC

Detailed Description

The MAX9938 unidirectional high-side, current-sense

amplifier features a 1.6V to 28V input common-mode

range. This feature allows the monitoring of current out

of a battery with a voltage as low as 1.6V. The

MAX9938 monitors current through a current-sense

resistor and amplifies the voltage across that resistor.

The MAX9938 is a unidirectional current-sense amplifier

that has a well-established history. An op amp is used

to force the current through an internal gain resistor at

RS+, which has a value of R1, such that its voltage drop

equals the voltage drop across an external sense resis-

tor, RSENSE. There is an internal resistor at RS- with the

same value as R1 to minimize offset voltage. The cur-

rent 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 gain resistor, ROUT. This

produces an output voltage, VOUT, whose magnitude is

ILOAD x RSENSE x ROUT/R1. The gain accuracy is

based on the matching of the two gain resistors R1 and

ROUT (see Table 1). Total gain = 25V/V for the

MAX9938T, 50V/V for the MAX9938F, 100V/V for the

MAX9938H, and 200V/V for the MAX9938W. The output

is protected from input overdrive by use of an output

current limiting circuit of 7mA (typical) and a 6V clamp

protection circuit.

Table 1. Internal Gain Setting Resistors (Typical Values)

GAIN (V/V)

200

100

50

25

R1 (Ω)

100

100

200

400

ROUT (kΩ)

20

10

10

10

6 _______________________________________________________________________________________

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