Motorola MCF5281 사용자 설명서

27-70

MOTOROLA

 

The current into the signal (I

INJN

 or I

INJP

) under negative or positive stress is determined by

these equations:

Where:

V

Stress 

= Adjustable voltage source

V

EB

 = Parasitic PNP emitter/base voltage 

V

BE

= Parasitic NPN base/emitter voltage 

R

Stress

= Source impedance (10 k

Ω resistor in Figure 27-50 and Figure 27-51 on stressed

channel)

R

Selected

 = Source impedance on channel selected for conversion

The current into (I

In

) the neighboring pin is determined by the K

N

 (current coupling ratio)

of the parasitic bipolar transistor (K

N 

‹‹ 1). The I

In

 can be expressed by this equation:

I

In

 = – K

N

 * I

INJ

Where:

I

INJ

 is either I

INJN

 or I

INJP

.

A method for minimizing the impact of stress conditions on the QADC is to strategically
allocate QADC inputs so that the lower accuracy inputs are adjacent to the inputs most
likely to see stress conditions.

Also, suitable source impedances should be selected to meet design goals and minimize the
effect of stress conditions.

R

STRESS

R

SELECTED

Adjacent

10 k

Ω

Signal Under

Parasitic

I

injP

I

IN

+

Stress

V

STRESS

Device

Signal

V

IN

V

DDA

AN

n

AN

n+1

IINJN

VStress VBE

–

(

)

–

RStress

---------------------------------------------

=

IINJP

VStress VEB

–

VDDA

–

RStress

-------------------------------------------------------------

=