infineon 2EDF7275K Driving CoolGaN GIT HEMTs 600 V User Guide

infineon 2EDF7275K Driving CoolGaN GIT HEMTs 600 V

About this document

Scope and purpose
This application note introduces the RC interface configuration for Infineon CoolGaN™ gate injection high electron mobility transistor (GIT HEMT) 600 V gate driving. First a brief introduction of Infineon’s CoolGaN™ GIT HEMT 600 V ohmic p-GaN structure and typical driving circuit is given. By using a dedicated/standard gate driver, CoolGaN™ GIT HEMTs can be driven easily through the RC interface. A step-by-step RC interface tuning guide is then given. Finally, typical RC interface configuration values are given in the form of look-up tables for different slew-rate requirements and target applications.

This application note is intended to be used as a quick-reference guide for RC interface design in driving Infineon CoolGaN™ GIT HEMTs (Figure 1). For a more in-depth explanation of the driving mechanism, please refer to Driving CoolGaN™ GIT HEMT 600 V high electron mobility transistors [1]. In addition, to get more insights on the gate drive requirements and driving solutions for CoolGaN™ GIT HEMTs, check out the available Whitepaper [4].

CoolGaN™ GIT HEMTs and CoolGaN™ IPS products

Intended audience
This application note is mainly targeted at application engineers and circuit designers using CoolGaN™ GIT HEMTs 600 V [2] and CoolGaN™ Integrated Power Stage (IPS) [3].

What are CoolGaN™ GIT HEMT and RC interface

Infineon’s CoolGaN™ GIT HEMT is a highly efficient GaN transistor technology for power conversion in the voltage range up to 600 V. CoolGaN™ GIT HEMT 600 V adopts an ohmic p-GaN gate structure. Relevant advantages of this construction include:
Positive gate threshold voltage
CoolGaN™ GIT HEMT is a normally-off device, and its improved figure of merit (FOM) makes it an ideal replacement for a silicon MOSFET in SMPS applications.
Robust and reliable gate drive
CoolGaN™ GIT HEMTs have diode-like input characteristics. This provides voltage clamp and helps avoid any overvoltage damage to the transistor gate.
Highly stable RDS(on) over drain current
During the CoolGaN™ GIT HEMT on-state, constant gate current enables independence of RDS(on) over drain current.

Although CoolGaN™ GIT HEMTs are robust enhancement mode devices, their gate module differs from a MOSFET, which behaves like a diode with a forward voltage VF of 3 to 4 V. Therefore, a continuous gate current Iss of a few mA is needed during the steady on-state, and high gate charging currents Ion and Ioff up to 1 A are needed for fast-switching transients. Since the switch is normally-off with a low threshold voltage Vth around 1.2 V, a negative gate bias during the off-state is needed to prevent false gate triggering in hard- switching applications. To avoid a dedicated driver with two separate on-paths and bipolar supply voltage, the RC interface is the gate drive circuit recommended by Infineon for CoolGaN™ GIT HEMTS 600 V GIT, which is shown in Figure 2.

Three components in the RC interface are included in the gating circuit:

• Rss: steady-state gate current tuning resistor
• Rtr: transient switching speed dv/dt tuning resistor
• CC: coupling capacitor as charge pump to provide fast-switching transient as well as negative gate bias
  Typical gate drive RC interface for Infineon CoolGaN™ GIT HEMT 600 V

RC interface advantages

Key advantages of the RC interface scheme include:

Ease of use
Negative gate voltage can be directly tuned with the RC interface configuration. No level-shift circuit is needed in the gate driver. The RC interface is compatible with dedicated/standard gate drivers.

Controllable dv/dt transient control
Turn-on/-off speed, on-state gate current and off-state reverse gate bias voltage are controllable thanks to the RC interface, which can be fine-tuned for EMI control, common-mode noise reduction and motor-drive applications.

Efficient drive
Negative gate bias is gradually discharged after the turn-off transient, which is beneficial for power loss reduction during operation in the third quadrant. The typical gating waveform of the Infineon RC interface and piecewise analysis of the gating procedure of CoolGaN™ GIT HEMTs are given in Figure 3 and Figure 4 respectively. During the gate-on transient, the fast-charging path is formed by Rtr and CC. After that, constant current is injected into the CoolGaN™ GIT HEMT gate through Rss during the transistor steady on-state. During the gate-off transient, gate charge is discharged through Rtr and CC. During the off-state, charge stored in the coupling capacitor CC is gradually discharged, which contributes to negative gate voltage -VN and then gradually decreases to -VNf.

Typical gate voltage of CoolGaN™ GIT HEMT

Typical gating procedure of CoolGaN™ GIT HEMTs

Tuning the RC interface

General tuning rules

Rss tuning
Rss is tuned according to gate voltage VDD, gate diode forward voltage drop VF (3~4 V), and desired on-state gate current Iss. Reference Rss selection in different RDS(on) devices is given in Table 1.

It should be noted that reference Iss and Rss values are given to maintain the device at low RDS(on) in typical applications. In low source current applications, dependence of device RDS(on) on Iss is low. In this case, a higher Rss value can be chosen to lower gate driver loss and achieve higher overall efficiency. In high source current applications, a lower Rss value should be used to maintain the device at the lowest RDS(on).

Please always refer to typical drain-source on-resistance curve in the CoolGaN™ GIT HEMT and CoolGaN™ IPS product datasheet for fine-tuning in different source current use cases.

Reference Iss value for different CoolGaN™ GIT HEMTs

Note:
Reference Rss values are given with VDD = 8 V.

Rtr tuning
Rtr is tuned according to the desired switching slew rate in different applications. In hard-switching conditions, low Rtr is desired to achieve a high slew rate and thus reduce hard-switching loss. A typical Rtr value for RDS(on,typ) = 140 mΩ device is within the range of 20 to 50 Ω with VDD = 8 V. This value can be scaled to other ohmic class devices according to the desired slew rate. In soft-switching conditions, selection of Rtr is uncritical.

Maximum source and sink current can be quantified according to:

CC tuning
CC is tuned according to the desired negative gate voltage bias -VN during the transistor off-state. VN must always be positive and can be quantified according to:

with QGeq denoting an equivalent switching gate charge (QGeq = QGS for a hard- switching system and QGeq ~ QGS + QGD for a soft-switching system).

In hard-switching conditions, VN is recommended around 4 to 5 V depending on circuit topology and slew rate, which should be designed according to a trade- off between false trigger immunity and third-quadrant.

Tuning the RC interface
operation loss. In soft-switching conditions, VN can be lowered down to 2 V or even close to zero in specific soft-switching topologies.

Reference RC interface tuning for typical applications

Hard-switching and soft-switching
In hard-switching applications, the turn-on slew rate should be well- controlled to achieve a trade-off between switching loss and drain-source voltage overshoot. Typical RC interface designs in hard-switching applications are given.

Typical RC interface designs in hard-switching applications

R DS(on,typ)| R DS(on,max)| R tr| R ss| C C| Turn-on slew rate| -V N
---|---|---|---|---|---|---
55 mΩ| 70 mΩ| 5.6 Ω| 470 Ω| 3.3 nF| ~ 105 V/ns| ~ -3 V
10 Ω| 470 Ω| 3.3 nF| ~ 90 V/ns| ~ -3 V
15 Ω| 470 Ω| 3.3 nF| ~75 V/ns| ~ -3 V
10 Ω| 470 Ω| 4.7 nF| ~ 90 V/ns| -4 V ~ -5 V
140 mΩ| 190 mΩ| 20 Ω| 1.8 kΩ| 1.5 nF| ~ 100 V/ns| ~ -3 V
27 Ω| 1.8 kΩ| 1.5 nF| ~ 80 V/ns| ~ -3 V
47 Ω| 1.8 kΩ| 1.5 nF| ~ 60 V/ns| ~ -3 V
20 Ω| 1.8 kΩ| 3.3 nF| ~ 100 V/ns| -4 V ~ -5 V

Note:
Reference values are given with EiceDRIVER™ 1EDi/2EDi series gate driver and VDD = 8 V. The slew rate in applications is subject to system design and PCB layout. Reference RC interface design for CoolGaN™ GIT HEMT in separate gate path applications
When designing a gate driver with a separate gate path, the RC interface can be configured with an independent transient gate-on resistor Rtr_on and gate- off resistor Rtr_off, as shown in Figure 5(a). For a gate driver with unified output, a diode in the gate-off loop can be installed to independently control the turn-on and turn-off speed as shown in Figure 5(b). In hard-switching applications, a larger Rtr_on is selected to avoid transistor drain-source voltage overshoot and a smaller Rtr_off is selected to guarantee sufficient damping of oscillations in the gate loop.

In soft-switching applications, simultaneous high current and high voltage in the power switching is avoided, which yields much slower voltage transients with typical slopes of only a few V/ns. Negative gate voltage bias (-VN) should be chosen to be as low as possible, recommended within -2 V. Rtr_on and Rtr_off are obviously less critical in soft-switching applications and can be chosen to be higher than in hard-switching applications.

CoolGaN™ IPS products

RC interface configuration in CoolGaN™ IPS products

The RC interface circuit is also compatible with CoolGaN™ IPS products. The same tuning circuit and methodology can be configured in half-bridge and single-channel products, as shown.

Motor-drive applications

CoolGaN™ GIT HEMTs are advantageous in motor-drive applications for their low switching loss, small form factor and high temperature stability characteristics. Considering the physical limitations of motor winding, the slew rate of CoolGaN™ GIT HEMTs should be largely reduced. To achieve this goal, the RC interface shown in Figure 7 should be configured.

Reference RC interface configuration for CoolGaN™ GIT HEMTs in motor-drive applications

Reference RC interface design for CoolGaN™ GIT HEMTs in motor-drive applications

R DS(on,typ)| R DS(on,max)| R tr_on| R tr_off| C C| R ss| C gd_ext| R damp| C gs_ext| Slew rate
---|---|---|---|---|---|---|---|---|---
270 mΩ| 340 mΩ| 200 Ω| 20 Ω| 3 nF| 2 kΩ| 5~9 pF| 50 Ω| 100 pF| ~ 5 V/ns
270 mΩ| 340 mΩ| 200 Ω| 20 Ω| 3 nF| 2 kΩ| w/o| w/o| 2 nF| ~ 10 V/ns

Note:
Reference values are given with EiceDRIVER™ 1EDi/2EDi series gate driver and VDD = 8 V. The slew rate in applications is subject to system design and PCB layout.

The RC interface values shown in Table 3 are given as reference design for motor-drive applications. A large gate-on resistor Rtr_on is selected to slow down the switching speed. A low gate resistance path formed by Rtr_off  and Doff provides safe turn-off conditions. Extra capacitance Cgs_ext and Cgd_ext is paralleled to the transistor input to slow down the switching speed to 5 V/ns and prevent false triggering. Rdamp is installed to the external Cgd_ext path to prevent unwanted gate ringing. For space-constrained applications, a high blocking voltage Cgd_ext capacitor is not wanted. In this case, a larger Cgs_ext can be selected to reduce slew rate down to 10 V/ns.

References

1. Application note: Driving CoolGaN™ GIT HEMT 600 V high electron mobility transistors
2. Infineon CoolGaN™ HEMT: https://www.infineon.com/coolgan
3. Infineon CoolGaN™ Integrated Power Stage (IPS): https://www.infineon.com/coolgan-ips
4. White paper: Gallium nitride – Gate drive solutions for CoolGaN™ GIT HEMTs.

List of abbreviations

• HEMT ………………………………………………………………………………………………………… high electron mobility transistor
• CoolGaN™ IPS ………………………………………………………………………………………….. CoolGaN™ Integrated Power Stage
• MOSFET ……………………………………………………………………………. metal-oxide semiconductor field-effect transistor
• SMPS …………………………………………………………………………………………………………………. switch-mode power supply
• RDS(on) ……………………………………………………………………………………………………………… transistor on-state resistance
• RDS(on,typ) ………………………………………………………………………………………. transistor on-state resistance typical value
• RDS(on,max) …………………………………………………………………………………. transistor on-state resistance maximum value
• VF ………………………………………………………………………………………………………………. gate diode forward voltage drop
• Vth ……………………………………………………………………………………………………………………………. gate threshold voltage
• Ion ………………………………………………………………………………………………………………………………………. gate-on current
• Ioff ………………………………………………………………………………………………………………………………………. gate-off current
• Rss ………………………………………………………………………………………………….. steady-state gate current tuning resistor
• Rtr ………………………………………………………………………………………… transient switching speed dv/dt tuning resistor
• Rtr_on …………………………………………………………………………………………………………………….. transient gate-on resistor
• Rtr_off …………………………………………………………………………………………………………………….. transient gate-off resistor
• CC …………………………………………………………………………………………………………………………… gate coupling capacitor
• -VN ……………………………………………………………………………. negative gate voltage at the start of transistor off-state
• -VNf ……………………………………………………………………………… negative gate voltage at the end of transistor off-state
• VDD ……………………………………………………………………………………………………………………………….. gate-supply voltage
• VGS ……………………………………………………………………………………………………………………………….. gate-source voltage
• Iss ……………………………………………………………………………………………………………………………….. on-state gate current
• Ion,max …………………………………………………………………………………………………….. transient maximum gate-on current
• Ioff,max …………………………………………………………………………………………………….. transient maximum gate-off current
• Qgeq …………………………………………………………………………………………………………… equivalent switching gate charge
• CGS ………………………………………………………………………………………………………………………… gate-source capacitance
• QGS ………………………………………………………………………………………………………………………………… gate-source charge
• QGD………………………………………………………………………………………………………………………………….. gate-drain charge
• Cgd_ext ……………………………………………………………………………………………………………….external gate-drain capacitor
• Cgs_ext ……………………………………………………………………………………………………………. external gate-source capacitor
• Rdamp ………………………………………………………………………….. damping resistor in external gate-drain capacitor path

Revision history

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E dition 2021-12-02

Published by

Infineon Technologies AG
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• © 2021 Infineon Technologies AG. All Rights Reserved.
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• AN_2107_PL52_2108_141427

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Except as otherwise explicitly approved by Infineon Technologies in a written document signed by authorized representatives of Infineon Technologies, Infineon Technologies’ products may not be used in any applications where a failure of the product or any consequences of the use thereof can reasonably be expected to result in personal injury.

References

• Semiconductor & System Solutions - Infineon Technologies
• Semiconductor & System Solutions - Infineon Technologies
• GaN HEMT – Gallium Nitride Transistor - Infineon Technologies
• GaN HEMT – Gallium Nitride Transistor - Infineon Technologies
• CoolGaN™ Integrated Power Stage (IPS) - Infineon Technologies

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