AN3271 datasheet(22/29 Pages) STMICROELECTRONICS

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High voltage connection

AN3271

22/29

Doc ID 17933 Rev 2

High voltage connection

Even if the maximum operating voltage of STM660x is 5.5 V, high voltage can be also

monitored based on the hookup shown in Figure 20. This extends the application scope to

devices such as notebooks, printers, network storages, etc. The supply voltage of the

application is limited by the maximum drain-source voltage of the P-channel transistor.

Figure 20.

High voltage connection

The STM660x device has active high enable output (EN).

The monitored voltage threshold is determined by resistors R1 and R2. The STM660x

current consumption has to be negligible compared to current through R1 and R2 in order to

not influence the monitored threshold (approx. 100 µA is recommended). The threshold

accuracy decreases with greater R1 and R2 resistors. With lower resistor values the

accuracy improves, but the overall current consumption increases.The value of resistors R1

and R2 can be calculated according to the following equation:

Equation 1

where

R1 is the first resistor of the voltage divider,

VSUPPLY–TH is the monitored threshold of the high voltage power supply,

VTH– is the undervoltage threshold of the STM660x,

I12 is the current through the R1/R2 divider.

SUPPLY

–

TH –

–

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