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

accurate 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

equivalent to the capacitance of the diode by itself. The

equivalent diagonal and adjacent capacitances can then

be calculated by the formulas given below.

In a quad, the diagonal capacitance is the capacitance

between points A and B as shown in the figure below.

The diagonal capacitance is calculated using the follow-

ing formula

CDIAGONAL = __C_1_x__C_2 + ___C_3_x_C_4

C1 + C2 C3 + C4

A

C1 C3

C

C2 C4

B

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

CADJACENT = C1 + _______1_____

–1– + –1– + –1–

C2 C3 C4

This information does not apply to cross-over quad

diodes.

Linear Equivalent Circuit, Diode Chip

Rj

RS

Cj

RS = series resistance (see Table of SPICE parameters)

C j = junction capacitance (see Table of SPICE parameters)

Rj =

8.33 X 10-5 nT

Ib + Is

where

Ib = externally applied bias current in amps

Is = saturation current (see table of SPICE parameters)

T = temperature, K

n = ideality factor (see table of SPICE parameters)

Note:

To effectively model the packaged HSMS-280x product,

please refer to Application Note AN1124.

SPICE Parameters

Parameter Units

BV V

CJ0 pF

EG eV

IBV A

IS A

N

RS Ω

PB V

PT

M

HSMS-280x

75

1.6

0.69

E-5

3.00E-08

1.08

30

0.65

2

0.5

3