January 14, 2020 by Luke James
Almost every modern electrical system uses switching power supplies. Due to its low current digital signaling, a microcontroller is not considered to be efficient in driving high power transistors of power supplies. Therefore, a gate driver is used to amplify the microcontroller output before it is fed into the input of a high power transistor.
In a nutshell, gate drivers act as interfaces between control signals and power switches. Maxim Integrated, a leading manufacturer of analog/mixed signal ICs has designed a family of CMTI isolated gate drivers (MAX22700–MAX22702) which can be used in numerous applications to drive high power transistors.
Maxim’s MAX22700–MAX22702 series is specifically designed to drive silicon-carbide (SiC) or gallium nitride (GaN) transistors in various inverter or motor control applications. They can also drive SiC or GaN field-effect transistors (FETs) with different output gate drive circuitry and B-side supply voltages. This family of devices offers high common-mode transient immunity, high electromagnetic interference (EMI) immunity, and stable temperature performance through Maxim’s proprietary process technology.
The devices feature variants with output options for gate driver common pin GNDB (MAX22700), Miller clamp (MAX22701), and adjustable UVLO (MAX22702).
Functional diagram of MAX22700-MAX22702 isolated gate drivers. Image credit: Maxim Integrated.
CMTI (Common Mode Transient Immunity) is the ability of an isolator to maintain safe and normal operation, while being subjected to a large common-mode transient on one or both sides of the isolator. CMTI is a critical specification for any gate driver to measure its robustness for handling differential voltages between two separate ground references. The typical value of for the MAX22700-MAX22702 series is 300kV/µs.
Isolation is required for any electrical system, where the individual parts have different ground potentials to prevent current flow during fault conditions. The MAX22700–MAX22702 provide basic galvanic isolation for digital signals transmitted between two ground domains, and block high-voltage/high-current transients. They can withstand differences of up to 3kVRMS for up to 60 seconds, and up to 1.2kVPEAK of continuous isolation.
The Ultra-high CMTI isolated gate drivers evaluation kit. Image Credit: Maxim Integrated.
The MAX22700–MAX22702 gate drivers operate at an ambient temperature up to +125°C on a standard multilayer PCB. They enter thermal shutdown mode when the junction temperature of the device exceeds +160°C (typ). During thermal shutdown, the output is set to logic-low to turn off the external power transistor regardless of the state of the MAX22700–MAX22702 inputs.
The MAX22701 features an active Miller clamp to prevent false turn-on of the external power transistor caused by the Miller current.
The MAX22702 features an adjustable B-side UVLO (Undervoltage-Lockout) to accommodate UVLO requirements of different types of external power transistors.
With new power transistors, such as Silicon MOSFETs and GaN transistors being increasingly used in modern electrical and power electronics systems, it has become necessary to use special drivers instead of microcontrollers for switching.
Since the MAX22700-22702 series provides high CMTI, short propagation delay, built-in galvanic isolation, they can ensure the highest switching speeds for SiC or GaN transistors in a broad range of applications such as UPS/PV Inverters, motor drives, and more.
