Diodes Incorporated Debuts New Bidirectional Current Monitors
The fresh series is designed to measure particularly low-sense voltages, enabling inexpensive, low-value shunt resistors to monitor large currents.
Introduced July 13, Diodes Incorporated’s ZXCT199 series current monitors are bidirectional, single-stage instrumentation amplifiers designed to accurately measure minute sense voltages across a wide range of common-mode voltages.
ZXCT199 series members are designed to accurately measure minute sense voltages. Image used courtesy of Diodes Incorporated
The units’ low offset voltage and zero drift architecture enables them to accurately measure current passing through shunts even with a voltage drop as low as 10mV full-scale, the company said in its announcement release. This allows high currents to be measured across inexpensive, small-value resistors, Diodes noted.
One New Series, Nine New Members
The ZXCT199 series sports nine members, whose available gains cover 50, 100, and 200 V per V.
As illustrated in the series datasheet, those gains are stable up until just under 10 kHz, with all three derateing to zero at frequencies above 1.2 MHz.
Gains for ZXCT199 series members derate past 10 kHz. Image used courtesy of Diodes Incorporated
At each of the three gain points, Diodes Incorporated offers variants featuring offset voltages (Vos) of either ±80, ±100, or ±150 microvolts.
Basic Operational Theory
As depicted below, the current to be measured passes through the shunt resistor. Some power must be wasted crossing the resistor (P = I2R), so its resistive value must be as low as is practicable. Because E = I x R, the voltage across the shunt is directly proportional to that current, and because the resistive value is low, so too will be the voltage measured across it.
A typical application circuit for the ZXCT199 series of current monitors. Image used courtesy of Diodes Incorporated
That tiny voltage, directly proportional to the current being measured, is fed into the op amp. Depending on which ZXCT199 version is chosen, the measured voltage is multiplied by either 50, 100 or 200, and is thus more easily measured by other system components and readily converted into the current’s value.
Design Considerations and Key Device Specifications
These current monitors operate with an unusually wide supply range of 2.7 to 26 volts, and draw a maximum current of 100 microamps. Per Diodes, these wide allowable supply voltages provide engineers significant design flexibility.
Inputs and Outputs
ZXCT199 series members can measure voltages across shunts at common-mode voltages from -0.1 to 26 V. An important consideration for this series is that members can measure inputs greater than the power supply’s voltage.
To protect the components that read the current monitor’s output, a 5-volt power supply will ensure non-hazardous voltage to 5 V devices, such as analog-to-digital converters (ADC). Another alternative is to employ a voltage divider at the ZXCT199’s output.
Gain Error and Drift
The maximum gain error over the specified temperature range is 0.8%. Zero-drift performance is at a maximum of 0.5 µV/℃.
Applications include battery chargers, high-side/low-side current sensing, large-scale computing, computer racks, server farms, high-performance video cards, industrial devices, robotic systems, power management devices, instrumentation, control systems, and metering devices
Specialized Automotive Applications
Diodes can produce specialized versions of these current monitors for automotive OEMs that require specific change control. Per the series' product page, the company can qualify parts to AEC-Q100/101/104/200 and PPAP, and manufactures in IATF 16949-certified facilities.
All members of the ZXCT199 series operate from -40 to +125 ℃ and are available in SOT363 packages.
The units are “Green,” meaning they contain no halogen or antimony. They are also lead-free and RoHS-compliant.