Motorola MCF5282, MCF5281 user manual Iinjn, Iinjp

Models: MCF5282 MCF5281

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Signal Connection Considerations

 

 

 

VSTRESS

 

RSTRESS

 

IinjP

AN

Signal Under

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

n

 

Stress

VDDA

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

+

 

10 kΩ

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Parasitic

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

RSELECTED

 

IIN

Device

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

VIN

Adjacent ANn+1 Signal

Figure 27-51. Input Signal Subjected to Positive Stress

The current into the signal (IINJN or IINJP) under negative or positive stress is determined by these equations:

IINJN

=

–(VStress – VBE)

--------------------------------------------RStress

 

 

IINJP

=

VStress – VEB – VDDA

------------------------------------------------------------RStress-

 

 

Where:

 

 

VStress = Adjustable voltage source

VEB = Parasitic PNP emitter/base voltage VBE= Parasitic NPN base/emitter voltage

RStress= Source impedance (10 kΩ resistor in Figure 27-50and Figure 27-51on stressed channel)

RSelected = Source impedance on channel selected for conversion

The current into (IIn) the neighboring pin is determined by the KN (current coupling ratio) of the parasitic bipolar transistor (KN ‹‹ 1). The IIn can be expressed by this equation:

IIn = – KN * IINJ Where:

IINJ is either IINJN or IINJP.

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.

27-70

MCF5282 User’s Manual

MOTOROLA

Page 654
Image 654
Motorola MCF5282, MCF5281 user manual Iinjn, Iinjp