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MAX9643

60V High-Speed Precision Current-Sense Amplifier

Maxim Integrated 

MAX9643

60V High-Speed Precision Current-Sense Amplifier

Detailed Description

The MAX9643 is a high-speed precision current-sense

amplifier ideal for a wide variety of high-performance

industrial power-supply applications. The device’s low

input offset voltage, tight gain error, and low temperature

drift characteristics allow the use of smallsense resistors

for current measurements to improve power-supply con-

version efficiency and accuracy of measurements. Its fast

response allows it to react quickly to switching currents as

is common in power-supply circuits, and makes it possible

to be used as part of control loops.

The unidirectional high-side, current-sense amplifier also

features a wide -1.5V to +60V input common-mode

range. This feature allows monitoring of power-supply

load current even if the rail is shorted to ground. Highside

current monitoring does not interfere with the ground path

of the load being measured, making the IC particularly

useful in a wide range of high-reliability systems.

The IC has been designed on a proprietary high-speed

complementary BiCMOS SOI process. This high-voltage

analog process is optimized for excellent AC dynamic per-

formance, ultra-low noise, wide operating voltage range,

and low-drift signal conditioning circuitry.

Applications Information

Internal Charge Pump

An internal charge pump on the part is utilized to provide

two attractive application features:

• Input common-mode voltage range extends to 1.5V

below ground.

• Output voltage range extends down to true ground.

A 250kHz internal charge pump is used to generate a

negative voltage rail to bias both the input stage and

output stage of the current-sense amplifier. Use a 1µF

ceramic capacitor between the CP1 and CP2 pins of the

IC, and ensure a tight layout to minimize loop area. Using

a 1µF ceramic capacitor from VEE to GND is essential to

good low-noise performance.

It is possible to also connect the VEE pin directly to an

external -5V power supply. Ensure that this voltage is

lower than the internally generated charge-pump voltage.

The -4.7V voltage is the minimum necessary to guarantee

the charge pump is turned off.

The MAX9643 EV kit shows a good example layout. A

representation is shown in Figure 1.

Input Common-Mode Voltage Range

The use of an internal negative voltage rail for its input

stage allows the current-sense amplifier to extend its

input common-mode voltage below ground without any

crossover inaccuracies. Crossover problems with preci-

sion can occur with alternate architectures of current-

sense amplifiers that use two different input differential

stages to cover the entire operating common-mode volt-

age range (either npn/pnp transistors or pnp transistor

and resistor-based input stages).

The minimum input common-mode voltage capability is

dependent on the internal negative voltage rail generated

by the charge pump. Since this negative voltage rail goes

down at low values of VCC (i.e., when under 5V), the

minimum input common-mode voltage rail is also limited

at low VCC.

The negative input common-mode voltage specification

can be exceeded if the input current is limited to under

5mA. This is typically accomplished by using series input

resistors. The input ESD structure for negative input

common-mode voltages looks like 5 series-connected

diodes. Assuming an on-drop of 0.7V per diode, negative

FROM RSENSE

TO ADC

8765

Figure 1. PCB Layout

MAX9643

+

1 234

1µF

1µF

0.1µF

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