LMZ31506 and LM3880

takahiko yokota

Other Parts Discussed in Thread: LMZ31506, LM3880

My customer will use LMZ31506 and LM3880 under Vin=12V and control enable of LMZ31506(INH terminal) by LM3880.

As long as I watched 4page of attached document, I think the voltage level of flag terminal is under 5V. When they have simulated it by LTspice, the voltage level of INH terminal was 8.5V.

But this voltage is over absolute maximum rating of LM3880's flag terminal.

Could you tell me internal resister and voltage level of LMZ31506's INH terminal when Vin is 12V, Output pulling up is 5V and 100kΩ?

http://www.tij.co.jp/jp/lit/df/tidrcm6/tidrcm6.pdf

Best regards,

Yokota

over 9 years ago

0 Frank De Stasi over 9 years ago

TI__Guru 72845 points

Let me pass this to the correct engineer.

0 J Arrigo over 9 years ago

TI__Mastermind 28020 points

The LMZ31506 INH pin has an internal pullup current source, allowing the user to float the INH pin for enabling the device. The pull-up voltage level is approximately 2.8V when this pin is floating. There is no internal resistor divider on this pin.

0 takahiko yokota over 9 years ago in reply to J Arrigo

Mastermind 7135 points

Thank you for the answer. I'll give a reply it to my customer.

But I have a question. The result of LTspice was 8.5V, can I think it is wrong?

Best regards,

Yokota

0 J Arrigo over 9 years ago in reply to takahiko yokota

TI__Mastermind 28020 points

The LMZ31506 will not pull the voltage up to 8.5V. The simulation may be incorrect.
Please verify that there is no other voltage being applied to the INH/UVLO pin of the device.

0 takahiko yokota over 9 years ago in reply to J Arrigo

Mastermind 7135 points

Let me ask you two questions in addition.
1.
There are text "The Inhibit control has its own internal pull-up to VIN potential" at 20 page of LMZ31506's datasheet.
Can I think that the INH terminal is 2.8V regardless of Vin as long as Vin is more than 4.5V, INH is floating ?

2.
In Xilinx Zynq 8w power reference design, PVIN = VIN = 12V, INH terminal is pulled up 5V(100kΩ).
Is the voltage level of IHN terminal 5V in this case?

Best regards,
Yokota

0 J Arrigo over 9 years ago in reply to takahiko yokota

TI__Mastermind 28020 points

1. Yes, the INH terminal is 2.8V regardless of Vin
2. Yes, the INH terminal will pull up to almost 5V if a 5V/100kΩ pull-up is applied.

0 takahiko yokota over 9 years ago in reply to J Arrigo

Mastermind 7135 points

I'm sorry to add a question.

Could you tell me internal circuit of INH terminal?

Best regards,

Yokota

0 J Arrigo over 9 years ago in reply to takahiko yokota

TI__Mastermind 28020 points

The INH pin of the LMZ31506 is a direct connection to the EN pin of the internal controller. There is no additional circuitry on this pin.

0 takahiko yokota over 9 years ago in reply to J Arrigo

Mastermind 7135 points

If the INH terminal is 2.8V, I think it needs zener diode etc attached document(TPS625261 datasheet).

So if the INH terminal direct connection to the EN pin of the internal controller, I think it's voltage level isn't 2.8V.

What is correct?

Best regards,

Yokota

Power management

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LMZ31506 and LM3880