gan power system-in-package for efficient emobility · confidential information expectation of gan...

GaN Power System-in-Package

for efficient eMobility

Confidential information

▪ Expectation of GaN switches for high power applications:

from 6kW to 160kW

▪ Complications when reality meets expectations

▪ How to fulfill expectations using the package design and

functional partitioning

Outline


Expectation of GaN switches

▪ High Frequency Decrease magnetics size

▪ High Efficiency Cooling system would be simpler

▪ High Power Density Decrease footprint & weight

COMMON EXPECTATIONS

Small and lightweight GaN based system!


Meeting with reality

▪ High Frequency High voltage & current spikes

▪ Reduced Frequency Again high voltage & current spikes

─ Increase trise/fall Increased power dissipation

▪ High power density Cooling system becoming complex

─ Increase # of transistors The whole system becoming expensive

COMMON COMPLICATIONS

GaN is amazing switch but end user did not gain much out of it…


How can we help

▪ Design the product to make life of designer easier

▪ Provide focused and customized support

▪ Make available relevant reference designs working for realistic

conditions


How can we help

▪ Design the product to make life of designer easier

▪ Solve part of the system challenges by package level integration


Requirement # 1: high frequency

Challenges of high current ( 50 A to 200A ) high frequency

switching are:

1. Simple and robust drive for high frequency switching

2. Fast rise and fall times


Requirement #1: Simple and robust drive for high frequency switching

▪ Two options could be considered for GaN:

▪ D-mode GaN requires negative voltage

▪ E-mode GaN has low VT and requires gate voltage swing from

negative to positive voltage


Requirement # 1: simple and robust drive

▪ Solution: Direct Drive circuit

▪ NOT a Cascode

▪ VT is + 5.5V , to be used with

standard drivers (like Si8239xISO)

with gate voltage 0V to +15V

VDD=+15V +15V

Gate signal: VG 0V to +15V

VGS (Q1) = -15V to 0V




▪ NOT a Cascode

▪ With driver protection


standard drivers (like Si8239xISO)

with gate voltage 0V to +15V

VDD=+15V +15V

Gate signal: VG 0V to +15V

VGS (Q1) = -15V to 0V




▪ NOT a Cascode

▪ With driver protection

▪ With Under Voltage Lock Out


standard drivers with gate voltage

0V to +15V

+15V

Gate signal: 0V to +15V

VGS (Q1) = -15V to 0V

VDD=+15V


Requirement # 2: Fast rise and fall times

▪ Challenge is in fast rise and fall times:→Requirements for

low inductance

Low inductance → low

voltage spikes

∆𝑉 = 𝐿 ×𝑑𝐼

𝑑𝑡

350 kHz HB buck


Requirement # 2: Fast rise and fall times

▪ Low inductance: 2 nH

Leadless SMT packageHigh number of parallel wires

High number

of parallel

wires


Requirement # 3: Over current protection

▪ Challenge: Avalanche voltage of GaN HEMT is well above

breakdown voltage of dielectrics → no avalanche

mechanism to release high current surge

▪ Solution: over current protection circuit



▪ Challenge: provide noiseless current

sense

▪ Using LV MOSFET for current sense

reduces noise and improves

stability RDSON =1.5 mOhm



▪ Solution: Over current

protection circuit

▪ Using LV MOSFET integrated

into the package

▪ Resulting in OCP circuit with

reaction time below 200 ns

GaN

GaN

Deadtime

control

UVLO

Isolation

Vref

Comp

Current sense

Vaux

Speed control

40nSec

40nSec

20nSec

135nSec

Current

Voltage on input of comp.

Current

Voltage on

input of comp.

Current Sense

Control circuit


Requirement # 4: Easy cooling solution

▪ Challenge: Heat transfer to a

heatsink for high power density

GaN die

▪ Solution: Low cost and high

thermal conduction EMPACK

solution. AlN ceramic under the

GaN die→ 2.4 kV isolation

Tθ = 0.3 K/W

No thermal pad is required;

2.5 kV isolated package


Requirement # 4: Easy cooling solution

6kW @ 350kHz hard switching

buck converter

Midpoint Voltage

Inductor Current ≈25A

60°C TJ on High Side

Mid Point Voltage; 200V/div

TRISE=6.3 ns; TFALL= 7.8 ns

60⁰C


Package level integration to ease system design

→ Low inductance

→ High & stable threshold

→ Over current protection

→ AlN-based EMPACK package

low voltage spikes @ fast

rise/fall time

use proven MOSFET driver

solutions

overcome avalanche

deficiency

low thermal resistance to

heat sink

Confidential informationConfidential information

Couple of practical examples


On-Board-Charger ref. design

21

▪ Smallest 6.7kW / 2.3L OBC available

▪ 3kW/L ➔ high power density


Inverter mode: one V22N65ACA per 8 KW of delivered power

▪ FB CCM Hard switching; 80 kHz ; peak current IOUT(peak) = 52A

▪ TJ is below 50°C;


Low voltage spikes

520V input voltage Buck hard switching @5kW 98.9%


Right integration of low RDSON GaN die enables high

power density with high efficiency

Summary

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