SBASAJ7A June 2022 – August 2022
PRODUCTION DATA
DC link overcurrent detection is a common requirement in DC/DC converter and motor-drive designs. Although the inductor current of a DC/DC converter or the phase currents of a motor drive are typically sensed for control purposes, phase current monitoring alone is not sufficient to detect all possible overcurrent conditions (such as shoot-through in the power stage). The most comprehensive way of implementing DC link overcurrent detection is to monitor the current in the DC+ and DC– lines. This detection, as illustrated in Figure 8-1, can be achieved by monitoring the voltage drop across two shunt resistors.
The DC+ load current flowing through the shunt resistor R10 produces a positive voltage in respect to GND1 that is monitored by the AMC22C11-Q1. When the voltage drop across R10 exceeds the reference value set by the external resistor R11, the comparator trips and signals the overcurrent event on the open-drain output OUT.
The DC– load current flowing through the shunt resistor R20 produces a negative voltage in respect to GND1 that is monitored by a AMC22C12-Q1. When the voltage drop across R20 exceeds the reference value set by the external resistor R21, the comparator trips and signals the overcurrent event on the open-drain output OUT.
The open-drain outputs from both isolated comparators are shorted together to form a single alert signal to the microcontroller unit (MCU). Similarly, both LATCH signals are tied together and can be controlled by a single GPIO pin from the MCU.
The isolated comparator on the DC+ side requires a high-side power supply that is referenced to the DC+ potential. A low-cost solution is based on the push-pull driver SN6501-Q1 and a transformer that supports the desired isolation voltage ratings. The integrated low-dropout (LDO) regulator on the high-side of the AMC22C11-Q1 allows direct connection of the VDD1 pin to the transformer output and no further preregulation of the transformer output voltage is required.
The isolated comparator on the DC– side requires a high-side power supply that is referenced to the DC– potential. A common solution is to power the isolated comparator from the low-side gate driver supply, as illustrated in Figure 8-1, or any other voltage supply referenced to DC–. The integrated low-dropout (LDO) regulator on the high-side of the AMC22C12-Q1 supports a wide range of input voltages and greatly simplifies the power-supply design.
The fast response time and high common-mode transient immunity (CMTI) of the AMC22C11-Q1 ensure reliable and accurate operation even in high-noise environments.