A high-voltage amplifier designed for bi-directional current sensing in the presence of fast switching common-mode voltages from -5 to 80V is available from Linear Technology. TheLT1999's input common-mode range is obtained with standard low voltage op amp supplies. A 2MHz bandwidth enables the amplifier to monitor currents in H-bridge motor controls, switching power supplies, solenoid, and battery chargers. It guarantees more than 80dB of common-mode rejection at 100kHz, even when monitoring motor and solenoid current, claims the company, ensuring that it remains insensitive to the large square wave input common-mode voltages present in these applications. A buffered output has three fixed-gain options for 10, 20 and 50V/V. As the output voltage is referenced halfway between the supply voltage and ground, the output can indicate both the magnitude and direction of the sensed current. In addition, the output bias level can be set via a separate input. Gain error is guaranteed at less than 0.5% and input offset voltage is guaranteed at less than 1.5mV over the full temperature range of -40°C to 125°C. The amplifier operates with an independent 5V supply voltage, drawing only 1.5mA while active and just 10µA in shutdown mode. The device is offered in an eight-lead MSOP or eight-lead SOP.
