DP83848I / resitor value for RD,TD and RBIAS pins

Ryuji

Guru 20090 points

Other Parts Discussed in Thread: DP83848I

Hello,

According to DP83848I datasheet P.33 , pull up resitors of RD+/-.TD+/-(13,14,16,17pin) are 49.9ohm.

Can we use 51ohm instead of 49.9ohm?

Regarding RBIAS, A 4.87kohm 1% resistor should be conected from RBIAS to GND.

Can we use 4.7kohm instead of 4.87kohm?

I would like to use E24 resistors.

Best Regards,
Ryuji Asaka　

over 11 years ago

0 John Hamilton1 over 11 years ago

TI__Intellectual 1885 points

Hello,

We do not recommend using resistor values other than the values listed in the datasheets and design guidelines.

Regarding the value of RBIAS, 4.87K ohm resistors must be used.

Thanks,

John

0 Ryuji over 11 years ago in reply to John Hamilton1

Guru 20090 points

Hello John san,

Thank you for the reply.

Could you please let me the concerning when we use the 4.7kohm for RBIAS and 51ohm for RD/TD?

Best Regards,

Ryuji Asaka

0 Patrick OFarrell over 11 years ago in reply to Ryuji

TI__Mastermind 31600 points

Ryuji-san,

The IEEE 802.3 specification defines the required 100BASE-TX VOD (Voltage Output Differential). Per the specification, this voltage must be 1V +/-5%.

The value of the RBIAS resistor and the termination resistors for RD/TD have a direct impact on this output voltage. If these vary by more than 1% from the stated datasheet values, compliance to the 100BASE-TX VOD cannot be guaranteed.

Patrick

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DP83848I / resitor value for RD,TD and RBIAS pins