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MAX9643
(Rev.:2011)

60V High-Speed Precision Current-Sense Amplifier

Maxim Integrated 

MAX9643

60V High-Speed Precision Current-Sense Amplifier

input voltage transients below -3.5V should be limited by

the use of input series resistors. For example, if an input

voltage transient or fault condition of -12V were to occur

in the application, use a resistor greater than 8.5V/5mA =

1700I. Use 2kI for margin.

The maximum input common-mode voltage extends up

to 60V over the entire VCC range of 2.7V to 36V. It is rec-

ommended to shield the device from overvoltages above

its 65V absolute maximum rating to protect the device.

Output Voltage Range

The internal negative voltage rail generated by the

charge pump is also used to bias the output stage of

the current-sense amplifier, allowing it to feature true

VOL = 0V performance. This feature allows small sense

voltages to be used and eases interface to other analog

and mixed-signal ICs. In reality, attaining true VOL = 0V

specification is usually limited by the offset voltage of the

current-sense amplifier since VOUT = VOS x gain, when

input VSENSE = 0V.

In addition, the maximum output voltage of the IC is inter-

nally clamped to less than 5V even when it is powered

from a 40V rail. This allows easy interface to low-voltage

downstream circuitry without worrying about protecting

them from large input voltage transients or faults.

Choosing the Sense Resistor

Choose RSENSE based on the following criteria:

U Voltage loss: A high RSENSE value causes the

power-source voltage to reduce due to IR drop. For

minimal voltage loss, use the lowest RSENSE value.

U Accuracy: A high RSENSE value allows lower currents

to be measured more accurately. This is because

input offset voltages become less significant when the

sense voltage is larger.

U Efficiency and power dissipation: At high current

levels, the I2R losses in RSENSE can be significant.

Take this into consideration when choosing the resis-

tor value and its power dissipation (wattage) rating.

Also, the sense resistor’s value might drift if it is

allowed to heat up excessively.

U Inductance: Keep inductance low if ISENSE has a

large high-frequency component. Because of the

high currents that flow through RSENSE, take care

to eliminate parasitic trace resistance from causing

errors in the sense voltage. Either use a four-terminal

current-sense resistor or use Kelvin (force and sense)

PCB layout techniques.

Power-Supply Bypassing and Grounding

For most applications, bypass VCC to GND with a 0.1FF

ceramic capacitor. In many applications, VCC can be

connected to one of the current monitor terminals (RS+

or RS-). Because VCC is independent of the monitored

voltage, VCC can be connected to a separate regulated

supply. There are no specific power-supply sequencing

issues to consider. The part can withstand 60V input

common-mode voltages even when VCC = 0V, and

maintains a high input impedance in this application

condition.

Chip Information

PROCESS: BiCMOS

Ordering Information

PART

PIN-

GAIN

PACKAGE (V/V)

TEMP

RANGE

MAX9643TATA+ 8 TDFN-EP*

MAX9643UATA+ 8 TDFN-EP*

2.5 -40NC to +125NC

10 -40NC to +125NC

+Denotes a lead(Pb)-free/RoHS-compliant package.

*EP = Exposed pad.

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