Si87xx-EVB
3.5. Adjusting Input Signal Frequency and VDD
Now is a good time to explore some additional functionality of the board. From here the user can do the following:
1. Slowly adjust VDD down to 3 V and up to 30 V. Then, take the VDD voltage below 2.8 V. Once below 2.8 V,
it can be seen that the Si87xx’s UVLO turns on. In this condition, the output should turn off and is pulled to
VDD in which case the square wave disappears.
2. Next, adjust the supply back to 5 V.
3. Another dial the user can adjust is the frequency dial on the square wave generator. Turn this dial from tens
of Hz up to 15 MHz and observe the scope output.
Note: To alter the output drive strength, R4 can be adjusted. Feel free to vary the 348 (the default board setting) R4 to sev-
eral k. Changing this value alters the rise/fall times at the expense or benefit of power consumption. Consult the prod-
uct data sheet as higher value resistors will not accommodate full 30 V operation.
3.6. Enable Test (DIP8, SOIC8, and LGA8 Boards Only)
The next test demonstrates the ENABLE function of the Si8712. To perform this test:
1. Remove the shunt on J4.
2. Connect a clip-to-clip wire from P2, Pin2 (VE/VL) to P2, Pin4 (GND2).
3. The output should be pulled to VDD and the square wave turned off.
4. To resume normal operation, remove the clip-to-clip wire on P2, and reinstall the shunt on J4 (position 1-2).
3.7. Using the Internal Pull-Up Resistor (DIP8, SOIC8, and LGA8 Boards Only)
To use the internal Pull-up resistor, the user will need to:
1. Replace the default device with a Si8711.
2. Remove J5.
3. Move the shunt on J4 to position 2–3.
4. Any of the tests described above can now be repeated.
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Rev. 0.3
SILICONIMAGE [ Silicon image ]
