POWER AND LINEAR IC SOLUTIONS

Tiny Devices Suit Motion-Control Current Sensing

Powerful, inexpensive microcontrollers and DSPs have enabled rapid advances in motion control electronics. Despite the move to digital control in such applications, there remains a significant need for precision analogue circuitry such as Analogue/Digital Converters (ADCs) and current sense amplifiers.

The H-bridge power transistor topology is increasingly popular as a means of driving motors and other loads bidirectionally from a single power supply. In most cases, there is great value in monitoring the current delivered to the load and using this information real-time to provide operational feedback to the microcontroller or DSP.



Accurately measuring the load currents is best achieved using a pair of precision current sense amplifiers and an ADC. Linear Technology’s LTC6102 current sense amplifier, LTC2451 ADC and LT6660 voltage reference provide a complete and accurate solution for such requirements.

The LTC6102 current sense amplifiers monitor the supply current fed to each half-bridge. The sense resistors are held at a relatively constant common-mode voltage to preserve the fidelity of the Pulse Width Modulated (PWM) current waveform. Monitoring each half-bridge individually at the supply side readily enables detection and management of failed power device operation and load shorts to ground.

The LTC6102 offers 10µV maximum input offset voltage, 50nV/°C input offset drift (maximum) and low 3nA (maximum) input bias current. It also offers a wide 4V to 60V input range for high-side current sensing. It is available in tiny 3mm x 3mm DFN and MSOP packages.

The current sense amplifiers source a 1mA current at their output pins that is proportional to the voltage across the sense resistors. The amplifier’s output current can be measured by connecting a 1kΩ resistor to ground and monitoring the voltage across it with an ADC such as the LTC2451. With only a single LTC2451 ADC measuring both the LTC6102 amplifiers, the half-bridge drive circuit needs to be monitored to determine the direction of the current. This circuit allows the 16-bit ADC to measure an input of 0V to 1V.

The LTC2451 offers very good DC accuracy in tiny eight-pin 3mm x 2mm DFN and ThinSOT-23 packages. Integral NonLinearity (INL) is typically 2LSB, which is only 153µV based on the LTC2451’s 16-bit resolution. Maximum gain error for the device is only 0.02%.

The LT6660 low-noise voltage reference provides a 5V signal to the LTC2451’s supply and reference pins.

Features: LTC6102

• 10µV maximum input offset voltage
• 50nV/°C maximum input offset drift
• 3nA maximum input bias current
• Fast step response: 1µs
• Wide input range: 4V to 60V
• Output currents <1mA
• Power supply rejection ratio: 130dB minimum
• 3mm x 3mm DFN and MSOP packages

Features: LTC2451

• Rail-to-rail input range
• 0.02LSB RMS noise
• 2LSB INL with no missing codes
• 1LSB offset error
• Programmable conversions rate
• Low power: 400μA active, 0.2μA sleep
• Eight-pin (3mm x 2mm) DFN and ThinSOT-23 packages
• Maximum gain error 0.02%

For further information, to register your interest in a Free Demo Board*, or to obtain a copy of the latest Altera/LTC Development Tools Brochure, please click here

* Free demo boards are limited to current or potential Arrow customers with valid opportunities and are at the discretion of local Arrow representatives.