Microchip Technology MEC172 Series Layout Manual page 20

AN3759
2.12 VCI_IN Pins When Used as GPIO
All the VCI_IN pins can be used as GPIOs. The firmware must program the VCI_BUFFER_EN bit[6:0] at VCI Buffer
Enable Register to disable power up functionality on these VCI pins if these are used as GPIOs.
2.13 VSET Pin (MEC1725 Only)
The MEC1721/MEC1723 VSET pin is an input to the ThermTrip block which sets the ThermTrip shutdown temperature.
The system designer creates a voltage level at these input through a resistor connected to GND as shown in
9. The value of this resistor is used to create an input voltage on the TRIP_SET pin that is translated into a temperature
ranging from 60°C to 123°C; see the VSET Resistor Settings table in the MEC1721/MEC1723 PCS for these values
(see your Microchip representative for availability).
Note 1: VSET is designed to operate using a 1% resistor. If a 5% resistor is used, the decoded temperature may
have an error more than 1°C.
2: An open condition on the VSET pin is decoded as a minimum temperature threshold level.
FIGURE 2-9: VSET CIRCUIT
2.14 Guardian Connections (MEC1725 Only)
The Guardian block is a combination temperature sensor, voltage monitor, hardware set thermal monitor, and fan con-
troller. It monitors one internal diode and four external diodes. Details for this block are included in the MEC1721/
MEC1723 Data Sheet (or PCS). This section includes describes layout considerations for this feature.
2.14.1 THERMAL DIODE LAYOUT CONSIDERATIONS
2.14.1.1 Remote Diode Hardware Considerations
• The remote diode positive (+) and negative (-) tracks should be kept close together (a 10 mil track minimum width
and spacing is recommended), in addition a separation of the diode traces from any other trace by at least a 20 mil
spacing is recommended.
• Place a capacitor between the two leads, as close as possible to the MEC1721/MEC1723 chip. 470pF (beta
enabled) is used for the processor diode and 2200pF (beta disabled) is used for the 3904 diode.
• Both remote temperature sensor channel inputs should be terminated with a thermal diode, a transistor or resistor,
even if they are not used in the design. Transistors that are suitable for use are MMBT3904 or an equivalent. Ter-
mination resistor values for use can be from 510 ohm to 1K ohm, see
perature values for selected resistors.
DS00003759B-page 20
Figure • and Table 2-6 for generated tem-
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Figure 2-