Reference: TVS parameters and selection methods
TVS (Transient Voltage suppressor) or said transient voltage suppression diode. When TVS high energy tube ends is subjected to impact moment, it to 10 -12 order sec, which is a high impedance to a low impedance between the two electrodes, the absorption of up to several kilowatts of power surge, so that between the poles voltage clamped at a predetermined value, the effective protection of electronic circuits precision components, damage from various surge pulse.
A, TVS works
TVS protects against transient pulses, in parallel with the protected device. Under normal operating conditions, TVS the protected circuit presents a high impedance state, when the transient voltage exceeds the breakdown voltage V BR time, TVS provides a low impedance path for the transient current. To flow outside the device to be protected so that pulse current flows most TVS tube, by both ends of the voltage protection device is limited to the TVS clamping voltage across (Clamping volatage) , when the over-pressure disappears, TVS diodes in turn returned to a high impedance state . Which unidirectional TVS tube and bidirectional TVS tube VI characteristic curve shown in Figure 1 .
FIG 1 TVS tube characteristic curve
Two, TVS parameters
2.1, V C --Clamping Voltage @Ipp (maximum clamping voltage)
Means maximum clamping voltage suppress diode peak current transient voltage pulses the I PP voltage value when the presented ends, as shown.
2.2, V the RWM --Working Peak Reverse Voltage (maximum reverse voltage)
The I R & lt --Maximum @VRWM Reverse Leakage Current (maximum reverse leakage current)
Indicates maximum reverse voltage TVS tube when the maximum voltage is not turned on, generally V the RWM = (0.8 ~ 0.9) V BR , this time TVS only a small reverse leakage current of the I R & lt , as shown in FIG 1 .
2.3, V BR --Breakdown Voltage @I T (reverse breakdown voltage)
TVS tube by a predetermined test current the I T voltage, which is TVS turn-on voltage of the flag. TVS breakdown voltage of the tube has a ± 5% error range (without "A" is a ± 10% ).
2.4, P PP --Maximum the Power Pulse Peak (maximum peak pulse power)
Pulse peak power P PP means 10 / 1000us wave pulse peak current the I PP and the maximum clamping voltage Vc product, i.e., P PP = the I PP * V C .
2.5, C J --Junction Capacitance (junction capacitance)
Cj主要是指TVS连接GND和I/O时，具有的电容值。Cd为TVS管的引脚寄生电容，通信速率越高，线路上使用的ESD保护期间的结电容要越低，否则将破坏数据信号。
2.6、Ipp--Peak Forward Surage Current(最大脉冲峰值电流)
TVS管可以承受的最大脉冲峰值电流。
三、TVS选型
3.1、最大篏位电压Vc的选择
瞬变电压抑制二极管(TVS)的最大箝位电压不能大于被防护电路可以承受的最大电压，否则会对被保护器件造成损坏。
3.2、脉冲峰值电流IPP的选择
如果清楚了解流过TVS管的脉冲峰值电流时，可根据所需要的IPP和Vc计算瞬变电压抑制二极管的最大峰值脉冲功率，然后再选取合适的TVS管。如果无法确定TVS管的脉冲峰值电流的大致范围，则尽量选用功率大的TVS管。当TVS管作为第二级保护时，一般使用500W~600W的器件就可以。
3.3、最大反向工作电压VRWM和击穿电压VBR的选择(二者定其一即可)
TVS管的最大反向电压VRWM不应低于电路的最大工作电压，一般可选择VRWM等于或略高于电路最高工作电压UM；按照VRWM=(0.8~0.9)VBR，击穿电压可按公式：VBRmin≥1.2UM或VRWM≥1.1UM选择。直流时，UM即为直流电压；交流时，UM为交流电压的有效值。
四、TVS使用注意事项
4.1、TVS管使用时，一般并联在被保护电路上，为了限制流过TVS管的电流不超过管子允许通过的峰值电流IPP，应在线路上串联限流元件，如电阻、自恢复保险丝、电感等。
4.2、当TVS管用于信号传输电路保护时，一定要注意传输信号的频率和传输速率，信号频率或传输速率较高时，应选用低电容值的TVS管。信号频率(传输速率)≧10MHz(Mb/s)时，Cj应该满足≦60pF;信号频率(传输速率)≧100MHz(Mb/s)时，Cj应该满足≦20pF。
4.3、TVS管所能承受的瞬态脉冲是不重复的，器件规定的脉冲重复频率(持续时间和间歇时间之比)为0.01%，如果电路中出现重复性脉冲，应考虑脉冲功率的累积，不然容易损坏TVS管。
五、TVS特点
优点：1、响应速度快(ps级)、瞬态功率大、漏电流低；
2、击穿电压有从6.8V~550V的系列值，便于各种不同电压的电路使用；
3、钳制电压较准确(±5%)；
缺点：1、结电容比较大(十几pF~几百pF);
2, surge resistance than the discharge capacity and the difference between the varistor, through the flow rate is generally 0.52A ~ 544A range ;