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MAX3232E: ESD countermeasure capacitor change

cafain
Mastermind 6775 points

Part Number: MAX3232E

HI Staff

MAX3232EIPWR

ESD countermeasure capacitor change

Let me ask you a question at PCN # 20210625000.1.

In the Rev E data sheet, a note was added that a capacitor of 1uF or more is required
between VCC and GND to meet the IEC 61000-4-2 standard (contact ±8 KV / air ±15 kV).

Currently, customers are using 0.1uF capacitors between VCC and GND.
(Before the datasheet Rev E is published)


In the following e2e, there is no silicon change, so in order to satisfy IEC61000-4-2, it is recommended to connect 1uF between Vcc and GND regardless of Rev in the data sheet. Was confirmed.
e2e.ti.com/.../max3232e-background-for-add-1-f-capacitor-on-new-revision-datasheet

Q1.
Currently, 0.1uF is connected between VCC and GND.
In this case, does the ESD withstand increase or decrease compared to 1uF?
(Will the ESD withstand voltage decrease?)

VCC-GND 1uF:
Contact ± 8KV
Air ± 15kV

VCC-GND 0.1uF:
Contact ±? KV
Air ±? KV

best regards
cafain

  • 0
    TI__Guru 53535 points

    Hi Cafain,

    As briefly mentioned in the linked thread, the external decoupling capacitors are used as an energy sink by the internal protection circuitry in the transceiver. Larger decoupling capacitors will be able to sink more energy and thus work better to aid internal protection. If there is only a small amount of capacitance available, the capacitor will charge fully and the voltage will rise, forcing the internal circuitry to dissipate the energy which can lead to damage. For this reason, we recommend ensuring that sufficient external capacitance is available in order to reach the specified ESD protection ratings. 

    The actual impact of certain capacitance values is difficult to measure due to the variables that can change between applications. We recommend a value of 1µF to ensure a minimum capacitance value is available, but a discrete capacitor is not the only source of supply capacitance. Power supplies, board characteristics, trace length/thickness/proximity, other ICs, and decoupling capacitors can all add to the total supply capacitance. In many applications, these extra sources will be sufficient to meet the needs of this device to achieve the specified ratings. For those applications which may not have sufficient supply capacitance from these sources, an dedicated external capacitor may be needed. Because we cannot know the characteristics of every application, we recommend a standard value so that all implementations can achieve the specified ratings. 

    In short, with less supply capacitance, it is more likely that the internal protection circuitry will be strained. Adding this external capacitance ensures that the available energy sink is sufficient to meet the specified ratings. If you are unsure if the total capacitance of your supply rail can support this, we recommend a discrete addition. If you have bulk capacitance elsewhere on the board for example, this discrete addition may not be necessary. 

    Let me know if this explanation is clear and if you have any more questions.

    Regards,
    Eric Schott