HSMS-270x: first choice HBAT-540x: for higher voltage applications HSMS-282x: general purpose HSMS-280x: highest voltage

Features:

Key Parameters:

Speed :

10s of psec ( vs. 10's of nsec for Au doped PN) for all Agilent Technologies Schottky diodes

I_{f max} (maximum forward current) :

750 mA for HSMS-270x

250 mA for HBAT-540x

160 mA for HSMS-282x

70 mA for HSMS-280x
[values assume use of thermally superior SOT-323 package]

R_s (series resistance) :

0.65 for HSMS-270x

2.4 for HBAT-540x

7 for HSMS-282x

30 for HSMS-280x

Barrier height :

0.34 - 0.41 V for standard Schottky diodes

0.19 V for zero bias Schottky diodes

0.7 V for GaAs Schottky diodes

Breakdown voltage :

15 V for HSMS-270x

16 V for HSMS-282x

30 V for HBAT-540x

70 V for HSMS-280x

Typical Capacitance :

1.0 pF for HSMS-282x

2.0 pF for HSMS-280x

3.0 pF for HBAT-540x

6.7 pF for HSMS-270x

Markets:

Clamping Diode Terms

Speed

What:

how fast the diode can respond to a signal (alternately, how fast a signal can be clipped or clamped).

Goodness:

faster is better.

Forward Current of a Schottky Diode (I_f)

What:

The maximum forward current of a Schottky diode is measure of how much current the diode can sink. The forward current I_f is inversely proportional to R_s, V_f, and _jc, and can be calculated from:
I_f = [T_j - T_a]/[_jc R_s]
or
I_f = [T_j - T_a]/[_jc V_f]

Plots of I_f vs. V_f, and of T_j and P_diss vs. I_f can be calculated using the Mathcad worksheet SCHOTTKY.MCD

Since I_f is inversely proportional to _jc, it is very importat that a thermally efficient package be used. All four clamping diode families are available both SOT-23 and SOT-323 (SC-70) packages. The following table shows why the SOT-323 package is preferred for clamping applications.

package	lead material	thermal resistance
SOT-23	iron alloy	460 C/W
SOT-323	copper	100 C/W

Goodness:

higher is better.

Series Resistance of a Schottky Diode (R_s)

What:

Schottky diode resistance may be expressed as a series resistance R_s or as a dynamic resistance R_D. These two terms are related by the equation R_D = R_s + R_j, where R_j is the resistance of the junction. Junction resistance of a diode with DC bias is quite accurately calculated by R_j = 26/I_b where I_b is the bias current in milliamperes. Either resistance is a measure of the "loss" in the diode.

Goodness:

lower is better.

Barrier height

What:

The term "Barrier height" is related to the voltage required for a given current in a Schottky barrier diode. Low voltage corresponds to low barrier height. Barrier height also sets V_f, the voltage at which the diode starts to clip.

Goodness:

depends on the application - the V_f must match the desired clipping voltage.

Breakdown voltage (Vbr)

What:

the voltage a Schottky barrier diode can tolerate before being damaged.

Goodness:

In clamping applications, breakdown voltage only matters if an anti-parallel pair isn't used (most people use a pair), then a higher breakdown voltage is (usually) better, at the cost of increased R_s (current carrying capacity).