TVS Diode Selection Guide for 800V Electric Vehicle Systems: High-Voltage Platform Protection

Selecting a TVS diode for an 800 V EV system requires working backward from three hard constraints: the maximum DC bus voltage (typically 450–900 V in a charged 800 V platform), the available energy from the load-dump or regenerative transient, and the clamping voltage that downstream SiC or GaN devices can tolerate. This guide covers TVS selection for each subsystem in a 400 V and 800 V EV powertrain, with specific part numbers from ASIM's high-voltage TVS product line.

Why 800 V EV Systems Require Different TVS Components Than 12 V or 48 V Systems

In a 400 V or 800 V EV platform, the high-voltage battery pack charges to approximately 400–450 V (400 V platform) or 750–900 V (800 V platform) at full state of charge. Every TVS diode connected to that bus must have a standoff voltage (VRWM) above the maximum bus voltage — otherwise the TVS conducts during normal operation, dissipating power continuously until failure.

Critical rule: VRWM ≥ maximum DC bus voltage × 1.05 (minimum), ideally × 1.10.

Standard automotive TVS parts such as SM8S-series (VRWM up to approximately 80 V) or SMCJ-series (VRWM up to 440 V) are inadequate for 800 V main bus protection. ASIM's 15KPA and 20KPA series cover VRWM values from 440 V to 540 V with peak pulse powers of 15,000 W and 20,000 W respectively — designed for high-voltage EV and industrial applications.

What Are the TVS Requirements for Each 800 V EV Subsystem?

High-Voltage DC Bus (Main Traction Bus)

The main traction bus connects the battery pack to the motor controller (inverter). Transient events include:

· Load dump: Bus voltage spike when high-power load (e.g., traction inverter) suddenly disconnects

· Regenerative braking: Energy injection back into the bus during braking

· Pre-charge relay switching: Voltage step when pre-charge circuit connects battery to inverter capacitors

TVS specification for 800 V main bus:

Recommended ASIM parts for 800 V main bus:

The 15KPA series is suitable for 400 V platform (where bus voltage peaks near 450 V). The 20KPA series provides higher surge margin for applications with aggressive regenerative braking transients or high peak bus voltages.

On-Board Charger (OBC) AC Input

The OBC converts AC grid power (single-phase 220 V or three-phase 380 V) to DC at the HV bus voltage. The AC input is exposed to grid-side transients including lightning-induced surges.

Protection scheme (single-phase 220 V input):

AC L/N input → [GDT 600 V] → [MOV (varistor)] → [Common Mode Choke] → [SMCJ440V 1500 W TVS] → Rectifier

The TVS at the AC input (SMCJ440V, VRWM = 440 V) handles residual transients after the GDT and MOV handle the primary surge. SMCJ440V: VRWM = 440 V, PPPM = 1,500 W, SMC package.

OBC DC Output (HV Bus Side)

After the OBC converts AC to DC, the output rail connects to the HV bus:

· Nominal voltage: 350–420 V (400 V platform) or 700–900 V (800 V platform)

· Use same 15KPA/20KPA series as main traction bus

DC-DC Converter (HV-to-12 V)

The DC-DC converter steps down 400 V or 800 V HV bus voltage to 12 V for the low-voltage (LV) network. Both the HV input side and the LV output side require protection.

HV input side: 15KPA440A or 20KPA440A (same as main bus selection above)

LV output side (12 V):

ASIM SM6S15V (VRWM = 15 V, PPPM = 6,600 W) is designed for 12 V automotive systems and passes ISO 7637-2 load-dump pulses. Customers include Toyota and Harman programs.

SiC Gate Driver Protection

SiC MOSFET gate oxide is thinner than silicon IGBT gate oxide, reducing ESD tolerance. Most 1,200 V SiC devices specify Vgs max = ±25 V with ESD tolerance around 500–1,000 V HBM.

Gate protection requirements:

· Bidirectional TVS (gates swing positive and negative)

· VRWM = gate drive positive voltage (typically 18–20 V)

· Clamping voltage VC ≤ Vgs max (25 V for most 1,200 V SiC)

· Cj ≤ 50 pF (gate circuit is high impedance; large capacitance slows switching)

Recommended part: ASIM SMAJ20CA (VRWM = 20 V, bidirectional, VC max = 32.4 V, SMA package) or SMBJ20CA (SMB package for higher pulse power).

Placement: Mount the gate TVS with ≤ 5 mm trace length between the TVS and the gate pin. GND connection to the gate source, not the power ground.

Charging Port (GB/T 20234 DC Connector)

The Chinese DC charging standard GB/T 20234.3 uses a nine-pin connector carrying both power (DC+/DC−) and control signals (CP, CC1, CC2, CAN differential pair).

Power pins (DC+/DC−):

Same as main HV bus protection: 15KPA440A or 20KPA440A.

CP (control pilot) signal:

CP is a ±12 V PWM signal used for charge control protocol. Requires bidirectional TVS, VRWM = 12 V.

· Recommended: ASIM SMA04J12CA (VRWM = 12 V, bidirectional, 400 W, SMA package)

CC1/CC2 (connection confirmation):

DC level signals, ±12 V maximum.

· Recommended: ASIM SMA04J12B (VRWM = 12 V, bidirectional, 400 W)

CAN bus (A+/A− differential pair):

For CAN FD communication between vehicle and charger.

· Common mode choke: ASIM CMF1210UD101MST (100 Ω at 100 MHz)

· TVS: ASIM SMA04J12B × 2 (one per CAN line)

How Does an 800 V EV System Differ from a 400 V System in TVS Selection?

The SiC gate driver and 12 V LV-side TVS requirements are identical regardless of whether the HV platform is 400 V or 800 V.

What EMC and Reliability Standards Apply to EV High-Voltage TVS Components?

High-voltage TVS diodes used in EV systems are evaluated against:

ISO 7637-2: Road vehicles — Electrical disturbances from conduction and coupling. Defines test pulses 1–5b for 12 V system transients. The SM6S series is designed to absorb pulse 5a/5b load-dump waveforms.

ISO 16750-2: Road vehicles — Environmental conditions for electrical and electronic equipment. Defines voltage range, reverse polarity, and transient limits for automotive electronics.

IEC 61000-4-5: Surge immunity. 1.2/50 µs voltage waveform, 8/20 µs current waveform. Applies to EV charging equipment (OBC, DC charger) rather than vehicle-side electronics.

AEC-Q101: Automotive qualification standard for discrete semiconductors. ASIM's automotive TVS product line is evaluated per AEC-Q101 methodology. Customers should verify specific part qualification status with ASIM engineering before finalizing a design.

Frequently Asked Questions

Q: Can a 440 V VRWM TVS (15KPA440A) be used on an 800 V platform?

A: It depends on the actual bus voltage. In an 800 V platform, the battery pack can charge to 900 V at 100% state of charge. At 900 V, a TVS with VRWM = 440 V would be in full conduction — it cannot be used on the main bus. For 800 V platforms, select VRWM = 480 V (15KPA480A) or VRWM = 540 V (15KPA540A) depending on actual maximum bus voltage. For 400 V platforms (max ~450 V), the 15KPA440A is appropriate.

Q: Why use a 15,000 W or 20,000 W TVS when the transient event lasts only microseconds?

A: TVS peak pulse power ratings (PPPM) are specified at 1 ms pulse width. For shorter transients (8/20 µs waveform), the actual peak power capacity is higher due to thermal time constants. The 15,000 W or 20,000 W rating ensures the device survives the 1 ms standardized pulse — not that it continuously dissipates that power. This gives adequate margin for real-world transients including load-dump, regenerative braking, and relay bounce.

Q: How should a 15KPA-series TVS be mounted for best thermal performance?

A: The P600 package has a large-area cathode tab that acts as a heat spreader. Mount to a copper pour of at least 4 cm² connected directly to the vehicle chassis ground (GND/PE). For high-power applications (repeated transients at high frequency), use a thermally conductive paste between the package and any metal heatsink or PCB pad. Operating junction temperature should remain below 150 °C.

Q: Does ASIM supply automotive-grade TVS to Tier 1 suppliers?

A: Yes. ASIM manufactures TVS diodes used in programs at Toyota, Harman, and other automotive-adjacent customers. For Tier 1 supply chain qualification, ASIM can provide full PPAP Level 3 documentation, AEC-Q101 test reports for applicable parts, and traceability documentation. Contact ASIM at +86-400-014-4913 for automotive program inquiries.

Q: Is there an alternative to placing a single large TVS on the main bus?

A: In some designs, engineers use a crowbar (SCR-based) circuit upstream of a lower-power TVS, or place multiple TVS in parallel to increase total IPP. Parallel TVS diodes should be matched (same batch, same lot) to ensure current sharing. For 800 V systems, contact ASIM engineering to discuss whether a single 20KPA device or a parallel configuration better fits the system constraints.

About ASIM Electronics: ASIM (阿赛姆电子) is a Shenzhen-based manufacturer of ESD and TVS protection components, founded in 2013. The high-voltage TVS product line (15KPA and 20KPA series, P600 package) covers VRWM from 440 V to 540 V and peak pulse power from 15,000 W to 20,000 W — designed for 400 V and 800 V EV system protection. Full product line: 1200+ TVS models (200 W to 20 kW), 330+ ESD models, 118 common mode choke models. In-house EMC laboratory. Certifications: ISO 9001, ISO 14001, ISO 45001, QC080000, RoHS, REACH. Contact: +86-400-014-4913 | +86-18822897174 (WeChat) | asim@asim.com.cn