ST92F120JR9T datasheet(15/320 Pages) STMICROELECTRONICS

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ST92F120 - GENERAL DESCRIPTION

1.2.4.5 Power Supply and Ground

As already said for the I/O pins, in order to guaran-

tee ST9 compliancy with respect to Quality Assur-

ance recommendations concerning ESD and

Latchup, dedicated circuits are added to the differ-

ent power supply and ground pins (digital and an-

alog). These structures create preferred paths for

the high current injected during discharges, avoid-

ing damage to active logic and circuitry. It is impor-

tant for the system designer to take this added cir-

cuitry into account, which is not always transpar-

ent with respect to the relative level of voltages ap-

plied to the different power supply and ground

pins. Figure 7 shows schematically the protection

net implemented on ST9 devices, composed of di-

odes and other special structures.

The clamp structure between the VDD and VSS

pins is designed to be active during very fast tran-

sitions (typical of electrostatic discharges). Other

paths are implemented through diodes: they limit

the possibility of positively differentiating AVDD

and VDD (i.e. AVDD >VDD); similar considerations

are valid for AVSS and VSS due to the back-to-

back diode structure implemented between the

two pins. Anyway, it must be highlighted that, be-

cause VSS and AVSS are connected to the sub-

strate of the silicon die (even though in different ar-

eas of the die itself), they represent the reference

point from which all other voltages are measured,

and it is recommended to never differentiate AVSS

from VSS.

Note: If more than one pair of pins for VSS and

VDD is available on the device, they are connected

internally and the protection net diagram remains

the same as shown in Figure 7.

Figure 7. Power Supply and Ground configuration

VDD

VSS

AVDD

AVSS

VPP

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