Linear Design Features LTMag-V18N01-02-LTC4151-Z_Hou Technical Manual

DESIGN FEATURES L

Voltage and Current Monitoring from 7V to 80V in 3mm × 3mm DFN-10

by Zhizhong Hou

Introduction Accurate power supply voltage and with changing load current. This can current monitoring is increasingly The LTC4151 and result in the load seeing significant important in everything from in- ground noise during transient spiking

LTC4151-1 offer the benefits

dustrial and telecom applications to load currents. Worse yet, a failed or

of high side current sensing

automotive and consumer electronics. disconnected low side sense resistor

without any of the usual

A complete power monitoring system causes the load ground to be charged

typically includes a sense resistor, a complexity. Each integrates to the full supply voltage, presenting

precision amplifier, an analog to digital a precision high voltage a potential safety hazard. converter (ADC) and a proper interface amplifier and associated High side sensing avoids these prob- to report data to a host controller. The lems, but requires a number of high

level shift circuit for high

LTC411 and LTC411-1 combine all performance devices and interfaces.

side current sensing, a

of these components (except the sense For instance, a robust high side sense

precision voltage divider for

resistor) into one IC, resulting in a full amplifier is required to withstand

featured, rugged and simple-to-use supply voltage monitoring, high supply voltage or high voltage

solution for accurate high side cur- a 12-bit ADC and an I2C transients. Also, a precision level shift rent sensing and voltage monitoring interface—all in small MS10 circuit is needed to accurately trans- (see Figure 1). late the large supply-referred signals

or tiny 3mm × 3mm

to appropriate ground level signals

DFN-10 packages.

High Side vs for the ADC. Low Side Sensing

In a power monitoring system, the it is traditionally more difficult to Full Featured High Side, sense resistor can be placed either implement. High Voltage Digital Monitors

between the system ground and the Low side sensing is relatively simple The LTC411 and LTC411-1 offer the load (low side sensing) or between in concept and design, but a low side benefits of high side current sensing the system supply and the load (high sense resistor floats the load above without any of the usual complex- side sensing). For many applications, system ground. Thus, the ground ity, plus they provide supply voltage high side sensing is desirable, but potential seen by the load varies monitoring in the same package. Each

VIN 7V TO 80V

VIN SENSE+ SENSE–

LTC4151

ADR1 –+ SHDN

VREF = 2.048V

I2C SCL

12-BIT ADCMUX

6V µCONTROLLER

SDA 6V

GND ADIN

Figure 1. Full featured current and voltage monitor simplifies high voltage, high side sensing.

Linear Technology Magazine • March 2008