TPS650864: ILIM calculation (BUCK1,2,6)

PAN-M

Mastermind 8375 points

Part Number: TPS650864
Other Parts Discussed in Thread: CSD87381P

Hi,

Please teach me about ILIM calculation.
I calculate by Equation 1 and 2.

Equation 2
VOUT=0.85, Vin(min)=5, Lmax=0.47uH, fsw=2.2MHz
Iripple(min)=0.682

Equation 1
RDSON=1, ILIM=3, ILIMref=50uA
RILIM=553kohm

About 10kohm is implemented with the EVM.
The result of this calculation is different digit.

Is this calculation correct?

Regards,
PAN-M

Iripple(min)

over 5 years ago

0 Layne J over 5 years ago

TI__Genius 12735 points

Hi PAN-M,

Your calculations are correct given the values you are using. However, RDSON should be much much lower than 1 Ohm. Typical RDSON values are around 10-20 mOhms, which will decrease the value of RILIM you are calculating. The setup for the EVM will not match your calculations as the EVM uses different output voltage levels and current limits than you are using for your calculations.

Best regards,

Layne J

0 PAN-M over 5 years ago in reply to Layne J

Mastermind 8375 points

Can we use 15mΩ as a typical?
I want to use one value for calculate.

Regards,
PAN-M

0 Layne J over 5 years ago in reply to PAN-M

TI__Genius 12735 points

Hi PAN-M,

It depends on which external FETs are chosen for the buck you are calculating for. One of the FETs we recommend (depending on how much load current you will be using) is CSD87381P (datasheet here). This FET has an RDSON between 13-20 mOhm depending on your exact use case. You need to chose which FETs you will be using before you can accurately complete the RILIM calculations.

Best regards,

Layne J

0 PAN-M over 5 years ago in reply to Layne J

Mastermind 8375 points

Thank you, Layne.

PAN-M

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TPS650864: ILIM calculation (BUCK1,2,6)