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In the datasheet for a MCU, it is mentioned that TM "Test Mode" pin require an external pull down device.

But there is no details: If I will put pull down resistor, what value should I choose then ?

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    \$\begingroup\$ What's the voltage? I would ballpark it to 10 kohm and see if it works. \$\endgroup\$ – winny Jul 12 '16 at 7:21
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    \$\begingroup\$ If "Test Mode" is not something that you will use in your application, then I would just tie it to ground. \$\endgroup\$ – Mark Jul 12 '16 at 7:42
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The exact value may not be critical. Typical ballpark values range from 1k to 100k.

With a 1k resistor, lots of current flows through so it is considered "strong" or more immune to noise. This is at the expense of efficiency.

With a 100k resistor, little current flows through so it is considered "weak" or more susceptible to noise. In this case efficiency is improved.

If the device is used in a noisy environment you would typically favor a lower value pull down but if you have a low power battery operated device you would favor a higher value pull down resistor.

10k is a very commonly used value since its easily available and balances both of these concerns.

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