TRS3232E: Selecting External capacitor (voltage rating and Values)

Gumpol Gorjarernrut

Prodigy 70 points

Part Number: TRS3232E

Tool/software:

Hi,

I have question about selecting External capacitor (C1 to C4) to use with TRS3232EIDR for Vcc = 5V.

from datasheet,

C1–C4 = 0.1 μF at VCC = 3.3 V ± 0.3 V

C1 = 0.047 μF, C2–C4 = 0.33 μF at VCC = 5 V ± 0.5 V.

Questions are

1. How many minimum voltage rating for external cap.? is it depend on Vcc (cap. voltage > Vcc+our margin)?

I notice that design ref. use to 25V. (maximum Vcc of TRS3232E is 6V.) why they not select cap. voltage 10V or 16V?

2. What happen, incase we use C1 to C4 = 0.1uF with Vcc 5V?

Thank you.

10 months ago

0 Clemens Ladisch 10 months ago

Guru 321890 points

1. The capacitors must be able to handle double the supply voltage, i.e., 10 V. Ceramic capacitors reduce their capacitance when there is a DC bias (see, e.g., this paper), so there should be a headroom.

2. Correct operation is not guaranteed.

0 Ethan Sempsrott 10 months ago

TI__Mastermind 22442 points

Hi Gumpol,

1. This does depend on VCC. For 5V systems, 10V is the minimum recommendation (i.e. 2x VCC). But 16V or higher is recommended for that headroom that Clemens mentioned.

2. Operating outside the recommend capacitance values means we cannot fully support that devices operation. If you intend to have different VCC supply voltages, please reference the bottom row in Table 8-1 from the datasheet:

As a side note, this E2E page has references to common RS-232 design questions such as this: https://e2e.ti.com/support/interface-group/interface/f/interface-forum/1518337/faq-rs-232-transceiver-resources

This includes a document on charge pump capacitors and other useful resources which you might find helpful.

Let us know if that helps or if you have any further questions,

-Ethan

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TRS3232E: Selecting External capacitor (voltage rating and Values)