TRS3232E-Q1 VCC against Negative Voltage

Shinichi Yokota

Other Parts Discussed in Thread: TRS3232E-Q1

Hello,

I'm concerned about how TRS3232E-Q1 will withstand a negative voltage which could be applied to its V_CC pin. In the system, -32 V could be applied to the V_CC pin, but a resistor of 2.2 kΩ will be put on the V_CC line to prevent an excessive current flown out of the V_CC pin. A Schottky diode of about 0.35 V will also be added externally to the V_CC pin, therefore the negative voltage will be clamped to nearly -0.35 V at the V_CC pin.

Does TRS3232E-Q1's V_CC pin have an internal clamping diode against a negative voltage? I guess the data sheet's Absolute Max Rating of V_CC -0.3 V to 6 V suggests the existence of a diode inside the chip.
If the above is correct, a current of about 14.4 mA could be flown out of the V_CC pin when -32 V is applied through the 2.2-kΩ resistor. Could the device survive or damage?

Best regards,
Shinichi Yokota

over 9 years ago

0 Ron Michallick over 9 years ago

TI__Guru**** 170776 points

Shinichi,

There is a diode internal, but it isn't there to clamp. It is a parasitic (unneeded and unwanted) diode due to integrated circuit physics.

The Schottky diode will take most of the 14.4mA current so I see no problem with this.

When VCC power is normal, does it also pass through a 2.2 kohm resistor? (That would be a problem)

0 Shinichi Yokota over 9 years ago in reply to Ron Michallick

TI__Genius 9715 points

Ron-san,

Thank you for the feedback. Now I understand an excessive current will not flow out of the V_CC pin. However, what about a voltage? A V_CC voltage clamped by the external Schottky diode will be about -0.35 V. Will it violate the V_CC absolute Max rating?

Best regards,
Shinichi Yokota

0 Ron Michallick over 9 years ago in reply to Shinichi Yokota

TI__Guru**** 170776 points

Shinichi-san,

It does violate the letter of the specification.

However, it doesn't violate the reason for the specification, the reason is to prevent excessive current. -0.35V plus the series resistance will prevent almost all current flow.

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TRS3232E-Q1 VCC against Negative Voltage