LINEAR DESIGN FEATURES LTMag- V18N01-07-LT6105_6_7-Jett User Manual Technical Handbook

L DESIGN FEATURES

Versatile Current Sense Amplifiers Offer Rail-to-Rail Input, 150°C Operating Temperature

by William Jett and Glen Brisebois

Introduction

Fast and accurate current measure- 3V TO 36V

ment is required in an increasing number of electronics subsystems.

RSENSE

The list of applications that call for 100Ω

–IN+IN

current sensing includes diagnostic

system assessment, fault detection,

load protection and scaling, battery

“gas gauge” monitoring, and impend- ing component failure detection, to name just a few. The challenge is that

Q1 there is no one-size-fits-all solution for OUT VOUT

LT6106

200m V/A current measurement. For example, ROUT 1k

protection circuits often emphasize measurement speed, while battery applications usually emphasize ac- curacy and low power. Nevertheless,

Figure 1. Typical current sense application using the LT6106. Sense resistor is 20mΩ and gain is

design time can be reduced by using 10, so transfer function is VOUT/ILOAD = 0.2V/A. an accurate current measurement am- plifier with features suited to the task

AC CU RA CY FU LL CA LE

at hand, such as the latest members SOURCE

LT6105

–0.3V TO 44V

of Linear Technology’s current sense

VS 100Ω

amplifier family, the LT6105, LT6106 +IN

and LT6107. VOUT

RIN1 OUT

0.02Ω VOUT = 1V/A −(

The LT6105 is distinguished by its 100Ω IN

rail-to-rail inputs. It is a perfect fit ROUT

VS 4.99k IN

for automatic test equipment (ATE) IN IN IN

systems and other systems that use a

2.85V TO 36VTO LOAD

combination of fixed voltage supplies and programmable or switched sup- plies. The LT6105 features an input

Figure 2. Typical LT6105 connection. Sense resistor is 20mΩ and gain is 50, so the transfer

voltage range of –0.1V to 44V that function is VOUT/ILOAD = 1V/A. Note the wide input source. is independent of the power supply voltage. The supply voltage for the 250µV and the power supply rejection

LT6105 can be obtained from any of 106d B makes the accuracy almost LIMIT OVER TEMPERATURE

convenient source within the supply independent of supply.

range of 2.85V to 36V. For instance, a The LT6107 is functionally identical

TYPICAL PART AT TA = 25°C

programmable supply with an output to the LT6106, but provides guaran-

of 0V to 24V can be monitored while teed performance and specifications

the LT6105 is powered by a fixed 5V at junction temperatures up to 150°C.

LIMIT OVER TEMPERATURE

supply. This suits it to under hood automotive

The LT6106 is distinguished by and some industrial applications that –0.8 5A FULL SCALE RIN = 100Ω ease-of-use and accuracy in single can exceed 125°C for relatively short –1.0 RSENSE = 0.02Ω ROUT = 1k AV = 10 V+ = 3V

supply environments. Just add two periods of time. Input offset voltage is –1.2 resistors and tie the supply to the sense less than 400µV over the entire tem-

LOAD CURRENT (A)

resistor, and the device is configured perature range of –40°C to 150°C. As to measure currents in supplies from with the LT6106, two external resistors

Figure 3. Measurement accuracy vs load

2.7V to 36V. Input offset voltage is a low set the amplifier gain. current for the LT6106 and LT1607

Linear Technology Magazine • March 2008