Panjit Protection Devices

Standoff voltage (Vrwm) is the maximum voltage the TVS can withstand in normal operation without conducting. Selection guidelines: (1) Vrwm must be higher than maximum normal operating voltage

(2) Include margin for voltage tolerances and transients

(3) For 5V circuits: use 5.0V or 6.0V TVS

(4) For 12V circuits: use 15V TVS

(5) For 24V circuits: use 24V or 27V TVS

(6) For 48V circuits: use 48V or 51V TVS. If Vrwm is too low, TVS will conduct during normal operation causing failure. If Vrwm is too high, clamping voltage may exceed protected circuit rating. Always check both Vrwm and Vc (clamping voltage) specifications.

Select Vrwm above maximum normal voltage but ensure Vc is below circuit damage threshold.

Clamping voltage (Vc) is the maximum voltage across the TVS during a transient event when conducting peak pulse current. This is the voltage that your protected circuit will see during the surge. Critical considerations: (1) Vc must be below the damage threshold of protected components

(2) Check IC datasheets for absolute maximum voltage ratings

(3) Include safety margin - typically 10-20% below max rating

(4) Higher power TVS diodes generally have lower clamping voltage for same standoff voltage

(5) Bidirectional TVS have slightly higher Vc than unidirectional. Example: For protecting a 5V logic IC with 6V absolute max, select TVS with Vc < 5.5V at expected surge current.

Ensure Vc is below your circuit's maximum voltage rating with safety margin.

TVS power rating (PPPM) determines surge current capability: 400W (P4KE): Suitable for ESD protection and low-energy transients on signal lines. 600W (P6KE/SMBJ): General-purpose protection for power lines and I/O ports. 1500W (1.5KE/SMCJ): Higher surge capability for industrial and automotive applications. 5000W (5KP): Severe surge protection for load dump, lightning, and industrial transients. Selection depends on: (1) Expected transient energy

(2) Source impedance of transient

(3) Standards requirements (IEC, ISO)

(4) PCB layout and trace inductance. When in doubt, use higher power rating for margin. Automotive applications typically require 1500W-5000W for load dump protection.

Match TVS power rating to expected transient severity. Use higher rating for automotive and industrial applications.

TVS placement is critical for effective protection: (1) Place as close as possible to the connector or entry point - minimizes inductance between transient source and TVS

(2) Minimize trace length between TVS and protected line - reduces voltage overshoot due to trace inductance

(3) Use ground planes for low-impedance return path - reduces ground bounce during surge

(4) For differential pairs, place TVS across each line to ground and between lines

(5) Avoid vias between TVS and protected circuit if possible. Layout guidelines: Keep traces short and wide

Use Kelvin connections

Place TVS on same layer as protected traces when possible. Poor layout can reduce effective protection by 50% or more.

Place TVS at connector with minimal trace length. Use good grounding practices.

Unidirectional TVS: Conducts in reverse direction only

Suitable for DC circuits with known polarity

Lower clamping voltage for positive transients

Cathode connects to protected line, anode to ground. Bidirectional TVS: Conducts in both directions

Suitable for AC circuits or bipolar signals

Same clamping voltage for positive and negative transients

Can be used on any signal polarity. Selection: Use unidirectional for DC power rails (5V, 12V, 24V) for best protection. Use bidirectional for AC lines, data lines, and differential signals. In bidirectional TVS, two diodes are connected back-to-back, providing symmetrical protection. Clamping voltage is typically 10-15% higher than unidirectional for same standoff voltage.

Use unidirectional for DC, bidirectional for AC and data lines. Unidirectional provides better protection for known polarities.

Automotive load dump is a severe transient (ISO 7637-2 Pulse 5) caused by battery disconnect while alternator is charging. Characteristics: 12V system: up to 100V for 400ms

24V system: up to 200V for 400ms

Source impedance: 0.5-4 ohms. Protection strategy: (1) Use 5000W TVS diodes (5KP series) for primary protection

(2) Place TVS at power entry point with short traces

(3) Use unidirectional TVS for DC lines

(4) Add series resistance or inductance to limit current

(5) Consider TVS + fuse combination for complete protection. TVS selection: 12V systems: 5KP22A or 5KP24A

24V systems: 5KP36A or 5KP48A. Verify clamping voltage at expected surge current is below circuit maximum rating.

Use 5000W TVS diodes for load dump protection. Place at power entry with good layout.