Maxim Calls Its Isolated SiC Gate Driver “Best in Class” for Reducing Power Loss by 30%December 18, 2019 by Gary Elinoff
The MAX22701E features a typical 300kV/µs common-mode transient immunity (CMTI)—the "industry’s highest."
The MAX22701E is part of a family of single-channel isolated gate drivers composed of the MAX22700, MAX22701, and the MAX22702. These devices feature output options for GNDB, Miller Clamp, or Adjustable UVLO, respectively.
There are also two input configurations: the E version is for single-ended inputs with enable, and the D version is for differential inputs.
The MAX22701E isolated SiC gate driver. Image (modified) used courtesy of Maxim Integrated
The MAX22700–MAX22702 family member devices are designed to drive silicon-carbide (SiC) or gallium-nitride (GaN) transistors. Intended uses include switching power supplies, EVs, solar power inverters, and data farms.
What is Common-mode Transient Immunity?
Common-mode Transient Immunity (CMTI) is a way of categorizing a digital isolator's ability to operate when subjected to fast, transient voltage pulses. These common-mode pulses can appear on the transmitting side of the isolator, the receiving side, or on both sides of an isolator.
A device’s CMTI, often specified in volts per microsecond, is the maximum pulse that an isolator can be subjected to and still work safely within specified parameters.
Improved Power Efficiency
Maxim claims that the MAX22701E’s 300kV/µs CMTI is up to three times higher than the closest competitor, resulting in increased system uptime. A propagation specification of 35ns and a maximum 5ns propagation delay matching between the high-side and low-side gate drivers serve to reduce the driven transistor’s dead time.
Test circuit and timing diagram. Image from (PDF) Maxim Integrated
These features serve to improve power efficiency by up to four percentage points. As Maxim explains, in the 90% efficiency range, 1% in efficiency improvement results in about a 10% reduction of power loss.
As an example, improving efficiency from 90% to 94% leads to a roughly 30% to 40% reduction in wasted power.
Specifications of the Family
All members of the new family of isolated gate drivers support a minimum pulse width of 20ns with a maximum pulse-width distortion of 2ns.
The devices all support a CMTI of 300kV/μs (typ), and each can withstand a voltage rating of 3kVRMS for 60 seconds.
The units all have a maximum RDS(on) of 4.5Ω for the high-side driver. For the low-side driver, RDS(on) is 1.25Ω for the MAX22700 and the MAX22702; RDS(on) is 2.5Ω for the MAX22701.
For the high-side transistor, members of the MAX22700–MAX22702 family offer a typical output current of 4 amps. Typical low-side current for the MAX22700 and MAX22702 is 5.7 amps and 2.85 amps for the MAX22701.
Functional diagram of MAX22700–MAX22702. Image from Maxim Integrated
All members of the MAX22700–MAX22702 family are housed in 8-pin, narrow-body SOIC packages with 4mm of creepage and clearance. The packaging material features a minimum comparative tracking index (CTI) of 600V.
This gives it a group I rating in creepage tables. All units are specified for operation at ambient temperatures of -40°C to +125°C.
Evaluation and Support Tools
Maxim offers the MAX22700X–MAX22702X evaluation kits for customers working with any member of the new group of isolated gate drivers. There are two broad types of evaluation kits: the MAX22701EVKIT and the MAX22702EVKIT.
The MAX22700X–MAX22702X evaluation kits. Image from Maxim Integrated
In their various versions, they can help customers as they work with any members of the new family, including the (PDF) MAX22700D, MAX22700E, MAX22701D, MAX22701E, MAX22702D, and MAX22702E.
Around the Industry
The ISO5452 from Texas Instruments offers a 100-kV/μs typical CMTI at a VCM of 1500V. It is meant for use with IGBTs and MOSFETs.
Silicon Lab’s Si827x isolated gate drivers feature a 200 kV/μs CMTI and offer 60ns propagation times. This family of isolators is designed to work with MOSFETs and IGBTs as well as with SiC and GaN semiconductors.