Transconductance amplifier for buck-boost converter

An integrated circuit (IC) controller for a Universal Serial Bus (USB) Type-C device, the IC controller comprising:

• a buck-boost converter to switch an output voltage of a voltage bus of the USB Type-C device that can swing up to at least 24 volts;
• and
• an error amplifier coupled between an output and an input of the buck-boost converter, wherein the error amplifier comprises:
• an output pin coupled to a pulse width modulation (PWM) comparator of the buck-boost converter;
• a first transconductance amplifier to adjust an output current at the output pin, wherein the first transconductance amplifier operates in a constant voltage mode and comprises:
• a first positive input to receive a first voltage reference;
• and
• a first negative input coupled to a tap point of a voltage divider coupled between a voltage bus and a ground of the buck-boost converter;
• a second transconductance amplifier to also adjust the output current at the output pin, wherein the second transconductance amplifier operates in a constant current mode and comprises:
• a second positive input to receive a second voltage reference;
• and
• a second negative input coupled to a current sense amplifier, the current sense amplifier being coupled to a sense resistor positioned inline along the voltage bus.

A method of operating an error amplifier that comprises an output pin coupled to a pulse width modulation (PWM) comparator of a buck-boost converter, a first transconductance amplifier that operates in a constant voltage mode, a second transconductance amplifier that operates in a constant current mode, wherein the method of operating the error amplifier comprises:

• receiving, at a first positive input of the first transconductance amplifier, a first voltage reference;
• receiving, at a first negative input of the first transconductance amplifier, a voltage from a tap point of a voltage divider coupled between a voltage bus and a ground of the buck-boost converter;
• adjusting, at the output pin, an output current based on a voltage difference between the first positive input and the first negative input;
• receiving, at a second positive input of the second transconductance amplifier, a second voltage reference;
• receiving, at a second negative input of the second transconductance amplifier, a voltage of a current sense amplifier, the current sense amplifier being coupled to a sense resistor positioned inline along the voltage bus;
• and
• adjusting, at the output pin, the output current based on a voltage difference between the second positive input and the second negative input.