3

Quad Capacitance

Capacitance of Schottky diode quads is measured using

an HP4271 LCR meter. This instrument effectively isolates

individual diode branches from the others, allowing ac‑

curate capacitance measurement of each branch or each

diode. The conditions are: 20 mV R.M.S. voltage at 1 MHz.

Avago defines this measurement as “CM”, and it is equiva‑

lent to the capacitance of the diode by itself. The equiva‑

lent diagonal and adjacent capaci‑tances can then be cal‑

culated by the formulas given below.

In a quad, the diagonal capacitance is the capacitance be‑

tween points A and B as shown in the figure below. The

diagonal capacitance is calculated using the following

formula

where

T = temperature,

°K

n = ideality factor (see table of SPICE parameters)

Note:

To effectively model the packaged HSMS-281x product,

please refer to Application Note AN1124.

Linear Equivalent Circuit Model Diode Chip

ESD WARNING:

Handling Precautions Should Be Taken To Avoid Static Discharge.

SPICE Parameters

Parameter

Units

HSMS-281x

V

25

pF

1.1

eV

0.69

A

E‑5

A

4.8E‑9

N

1.08

Ω

10

V

0.65

2

M

0.5

1

1

1

1

–– + –– + ––

1

1

1

1

–– + –– + ––

The equivalent adjacent capacitance is the capacitance

between points A and C in the figure below. This capaci‑

tance is calculated using the following formula

This information does not apply to cross‑over quad di‑

odes.