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The picture below shows a pin on a voltage regulator that must be connected to the ground, so I am wondering why not connected this pin directly to ground without using the circuit shown in the picture. However, there is no recommendation in the datasheet of the regulator for connecting this pin.

enter image description here

Edit 1: The following is the complete schematic. It is from AWR1642BOOST datasheet.

enter image description here

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  • \$\begingroup\$ Because this leaves the option open to change the connection if you want between HI and LO. Did you read what the pin actually does in the datasheet? \$\endgroup\$ – DKNguyen Oct 30 '19 at 15:50
  • \$\begingroup\$ Where does this schematic come from? Usually a 0 Ohm resistor is used by the manufacturer to use the same circuit for different products. For a product A where the pin has to be connected to ground, the manufacturer would solder the 0 Ohm resistor, and for a product B where the pin must no be connected to ground the manufacturer would not put the resistor. \$\endgroup\$ – Wheatley Oct 30 '19 at 15:52
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    \$\begingroup\$ That's a nice short in that documentation. \$\endgroup\$ – Voltage Spike Oct 30 '19 at 16:16
  • \$\begingroup\$ I updated the question, please check! \$\endgroup\$ – Basel Tahboub Oct 31 '19 at 7:41
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This looks like bad documentation. The idea is you can pull the port SS_CTRL high to PMIC_1V8 or low to GND by populating R120 or R119 respectively. This would allow you to access both values without manufacturing two different boards.

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Note that since both resistors are shown as 0 Ohms, you would only install one of them. If you installed both, you would short the power supply.

Having the two resistor positions allows you to select either of two modes of operation when you build the board.

Without seeing the datasheet for the part, I can't say what the different modes might do.

When you ask for usage details of a specific part, you should provide a linnk to the appropriate datasheet, or at least provide the part number so we can make more informed comments.

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  • \$\begingroup\$ I got this schematic from AWR1642BOOST design document provided by Texas Instrument. I know that that it would short the circuit, but the schematic is as shown. \$\endgroup\$ – Basel Tahboub Oct 31 '19 at 7:39
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The schema is likely done this way to enable changing the regulator output voltage later, by just replacing the resistors. Here is the idea:

LM317 voltage regulator circuit

From http://www.learningaboutelectronics.com/Articles/How-to-connect-an-adjustable-voltage-regulator

Peter Bennett is right that both resistors must not be mounted at the same time, or you would have a short-circuit. Normally, only R119 would be mounted.

It's quite common to add 0-ohm resistors to designs, to allow easy modifications or tests. I recently added a 0-ohm on a power line only for the purpose of replacing it with a low-resistance shunt resistor to monitor the current of the device when evaluating the design.

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I have just checked the BOM for the project I am working on and found out that R119 is NOT FITTED on the PCB so its just pulled up.

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