MON35W42 datasheet(17/60 Pages) SMSC

17 / 60 page

Monitor over 4.096V voltage:

The input voltage +12VIN can be expressed using the following equation.

VINV

)

The value of R1 and R2 can be selected as 28K Ohms and 10K Ohms, respectively, when the input

voltage V1 is 12V. The node voltage of +12VIN will be subject to less than 4.096V for the maximum

input range of the 8-bit ADC. Similarly, the node voltage of 5VSB (measured standby power VSB for

ATX power supply) also can be monitored by using two series resistors R3 and R4 which can be 5.1K

ohms and 7.5K ohms so as to obtain the 5VSB as limited to less than 4.096V. Pin 33 is connected to

the power supply VCC at +5V. This pin supports two functions. The first function is to supply internal

analog power in the MON35W42 and the second function is to monitor the 5V input through internal

series resistors. The values of the two series resistors are 34K ohms and 50K ohms so that input

voltage to ADC is 2.98V which is less than 4.096V of the ADC maximum input voltage. The voltage

equation can be represent as follows.

VVCC

in '(

)

298

where VCC is set to 5V.

Monitor negative voltage:

The negative voltage should be connected to series resistors and a positive voltage VREF (equal to

3.6V). In Figure 11, the voltage V3 and V4 are two negative voltages, -12V and -5V respectively. The

voltage V3 is connected to two series resistors and is then connected to VREF which is a positive

voltage. The voltage at node N12VIN must be a positive voltage and will if the values of the two series

resistors are carefully selected. If the value of two series resistors are R5=232K ohms and R6=56K

ohm. The input voltage of node N12VIN can be calculated by the following equation.

NVIN

VREF

232

(

)

() (

)

where VREF is equal 3.6V.

If V5 is equal to -12V then the voltage is equal to 0.567V and the converted hexdecimal data is set to

35h by the 8-bit ADC with 16mV-LSB. This monitored value should be converted to the real negative

voltage and the voltage is calculated by the following equation.

NVIN

VREF

Where

- is 232K/(232K+56K). If the N2VIN is 0.567 then the V5 is approximately equal to -12V.

MON35W42 Datasheet(PDF) 17 Page - SMSC Corporation