LINEAR LTC2460 User Guide and Manual

DESIGN IDEAS L

3mm × 3mm, 16-Bit ADC Brings Accurate, Precise High Side Current Sensing to Tight Spaces

by Leo Chen

Introduction

Power monitoring circuits are increas- 4V TO 60V

ingly used throughout automotive, RIN

VSENSE

industrial, communications and 6mΩ

+IN –INS

computing applications as electronics

–+ –INF

designers strive to continually im- 5V

prove thermal performance, increase V+V– 0.1µF

efficiency and generally make their 0.1µF

products more “green.”

The problem is that power monitor-

VOUT CS, SCK, OUT LTC2460

ing always looks like the perfect feature LTC6102 IN SDI, SDO 16-BIT ADC

TO CONTROLLER

until space and cost constraints come ROUT

1k GND

into play. Power monitoring is usually ROUT VOUT SENSE RIN

considered an ancillary function, so its footprint should be as small as

Figure 1. A simple and compact high side current sensing solution that combines a high

possible to maximize space available

resolution DS ADC (LTC2460) with a high precision current sensing amplifier (LTC6102).

to the main application. The LTC2460 16-bit Delta-Sigma ADC solves the space and design cost problem when sense resistor and sources a propor- mum current out of its OUT pin. This paired with one of Linear Technology’s tional signal current. If the current is current is converted into a voltage current sense amplifiers, such as the monitored on a high voltage power sup- across the 1kΩ resistor to ground, LTC6102. ply, an accurate and precise current which allows the connected LTC2460 The LTC2460 proves that big-fea- sense amplifier, such as the LTC6102, to measure a 0V to 1V input. This input ture ADCs can come in tiny packages. is required to accurately resolve the range spans 80% of the ADC’s input It is available in a 3mm × 3mm DFN small voltage drop riding on the high resolution. Of course, the output of the (or a 12-pin MSOP), and integrates a common mode voltage. current sense amplifier can be scaled 10ppm/°C precision reference. The Typically the signal current pro- to use as much of the LTC2460’s input integrated reference paired together duced by the current sense amp is range as needed, while providing for with an extremely easy to drive input converted via a grounded resistor to a overrange conditions. stage (50n A average input current) properly scaled voltage, which, in this Another advantage to the LTC2460 makes it possible to use the LTC2460 case, can be measured directly using is the narrow input bandwidth of with little to no support circuitry. the LTC2460’s easy to drive input. approximately 30Hz. This provides

The 16-bit output data can then be excellent rejection of power supply

Measuring Power Means used to compute power consumption ripple noise, and allows accurate Measuring Current and efficiency. measurement of the DC component Measuring power supply input and of the current.

output voltages is fairly straightfor- Accurate, Precise and Very

ward, as any voltage can be scaled Compact High Side Current Conclusion

with a simple divider or amplifier and Sense Design The LTC2460 and the LTC6102 facili- compared to a voltage reference. Cur- Figure 1 shows a 48V, 8A current mea- tate a compact, high resolution, high rent measurement is generally more surement application. The LTC6102 accuracy current sense solution. The complicated, especially at commonly is a precision current sense amplifier LTC2460 is a 16-bit ADC in a tiny used high voltages such as –12V, 24V that offers 10µV maximum input off- package that includes an integrated and 48V. set voltage, 50n V/°C input offset drift precision reference, while the LTC6102 To measure current, a small sense (maximum), and low 3n A (maximum) provides high precision, current mea- resistor is placed directly in series with input bias current. surements that in turn can be easily the supply. A current sense amplifier This current sense amplifier has digitized by the ADC. L takes the small voltage drop across this zero-drift and sources a 1m A maxi-

Linear Technology Magazine • September 2009