LM25148-Q1: MOSFET selection and VCCX connection

Frank QIN

Part Number: LM25148-Q1

Tool/software:

Hi Team,

We have some discussion in this internal thread before, while customer's engineer want to directly have some further discussion here.

(1) LM25148-Q1: Schematic Review - Power management - INTERNAL forum - Power management - INTERNAL - TI E2E support forums

The main questions are about how to calculate the MOSFET spec for selection and VCCX connection.

Regards,

Frank

6 months ago

0 Frank QIN 6 months ago

TI__Expert 8930 points

Will let customer post the questions here.

Regards,

Frank

0 Dino Maslic 6 months ago in reply to Frank QIN

TI__Expert 5510 points

Not seeing any extra questions, all previous questions were answered in the above linked thread.

Thanks,

Dino Maslic

0 Shiyu Luo 6 months ago

Prodigy 110 points

1. Now you calculate the TYP value, how to determine the maximum and minimum values of HO and LO? Our MOS Vgsth=4.5V, is there already a risk?

2. About the VCCX pin, for our current application (input 9-16V, output 6.5V, current 7.2A;), how to connect this VCCX?

3.The value of the sensing resistance can be different from the calculated value, so how can the chip sense the required compensation value?

0 Shiyu Luo 6 months ago in reply to Dino Maslic

Prodigy 110 points

1. Now you calculate the TYP value, how to determine the maximum and minimum values of HO and LO? Our MOS Vgsth=4.5V, is there already a risk?

2. About the VCCX pin, for our current application (input 9-16V, output 6.5V, current 7.2A;), how to connect this VCCX?

3.The value of the sensing resistance can be different from the calculated value, so how can the chip sense the required compensation value?

0 Dino Maslic 6 months ago in reply to Shiyu Luo

TI__Expert 5510 points

Hi Shiyu,

1. The typ is lower than the threshold you have specified so not sure if this will work, may want to consider a different FET.

2. For VCCX, the absolute maximum voltage on the pin is 6.5V, TI recommends to use a 5V rail to connect to VCCX. 6.5V is the absolute maximum rating of the pin, so connecting a 6.5V rail to VCCX is not advised to do.

3.The sense resistor sets the current limit, so if there is some variance on the sense resistor the current limits will slightly differ. If you are worried about variation, you can use a resistor that has tighter resistance ratings.

Thanks,

Dino Maslic

0 Shiyu Luo 6 months ago in reply to Dino Maslic

Prodigy 110 points

1. Can the MOS of HO and LO be used only if the VGSth is lower than the typical value (4.2V)?

2.SO,How to use this Pin？connect it to VCC？

3.If the calculated value is 12mR, can 3mR be used and does the chip have an adjustment function?

0 Dino Maslic 5 months ago in reply to Shiyu Luo

TI__Expert 5510 points

Hi Shiyu,

1. Can you send me the part number of your MOSFET so I can take a look at it to clear up questions.

2. What pin are you referencing, I don't see SO?

3. If you use a 3m ohm resistor then the current limit will be higher.

Thanks,

Dino Maslic

0 Shiyu Luo 5 months ago in reply to Dino Maslic

Prodigy 110 points

1.OK；

2.VCCX

3.Just the current limit will be higher？

0 Shiyu Luo 5 months ago in reply to Dino Maslic

Prodigy 110 points

1.Part number：IAUCN04S7N056D

0 Shiyu Luo 5 months ago in reply to Dino Maslic

Prodigy 110 points

Could you please give me all your calculations for this IC?

0 Dino Maslic 5 months ago in reply to Shiyu Luo

TI__Expert 5510 points

Hi Shiyu,

In regards to VCCX you can connect it to a 5V rail as recommended in the datasheet, the absolute maximum voltage rating on the pin is 6.5V.

For the current limit, yes that is correct, the current limit will be larger with smaller sense resistor.

For your MOSFET, it looks like the HO voltage may be too low to drive this as you would like with 4.5V of gate voltage. The FET referenced in the datasheet is "IAUC60N04S6L039", this may be suitable for your application.

For the all the calculations, please see the datasheet, as well as the design calculator on the product's product page on TI's website, under "Design & development"

Thanks,

Dino Maslic

0 Shiyu Luo 5 months ago in reply to Dino Maslic

Prodigy 110 points

So,can we connect the VCCX to VCC Pin?

0 Dino Maslic 5 months ago in reply to Shiyu Luo

TI__Expert 5510 points

No you cannot connect VCCX to VCC, the VCCX pin is what powers VCC if it is above 4.3V. Needs to be an external rail.

Thanks,

Dino Maslic

0 Shiyu Luo 5 months ago in reply to Dino Maslic

Prodigy 110 points

1.May I ask whether IAUZ20N08S5L300 can meet the requirements；

2.In the current demand, is it possible to ground VCCX directly, and how much impact will it have on power consumption?

0 Dino Maslic 5 months ago in reply to Shiyu Luo

TI__Expert 5510 points

I cannot comment on the FET as I am not sure what your requirements are, please see application section of data sheet to see if your requirements match up to what the example application was designed for.

Grounding VCCX would make the device's LDO power off of VIN which would be less efficient than a 5V rail on VCCX.

Thanks,

Dino Maslic