LM5170-Q1: Function of R102

Jeff Xie

Part Number: LM5170-Q1

Hi all,

Customer want to know the function of R102. Although it is DNP, what is the original purpose as it is connected to IPK, not directly to GND?

Because INP internally has a current source, which will provide a 1V bias at 40.2k resistor.

over 5 years ago

0 Helen chen over 5 years ago

TI__Mastermind 40080 points

Hi Jeff,

The expert for this part is in US, they are currently on new years holiday. Please wait the answer in patience.

0 Youhao Xi over 5 years ago in reply to Helen chen

TI__Guru* 78400 points

Thank you Helen.

Hi Jeff,

This resistor helps to adjust the peak current limit between the buck and boost modes. According to the datasheet EC table, you can see that the buck and boost modes has different peak current limit settings. This resistor can help reduce the difference.

Thanks,

Youhao Xi, Applications Engineering

0 Jeff Xie over 5 years ago in reply to Youhao Xi

TI__Intellectual 1780 points

Hi Youhao,

Thanks for reply. But DIR is logic high in buck mode and logic low in boost mode. IPK buck is 46mV/V and IPK boost is 48mV/V.

When DIR is logic high, is IPK voltage determined by the resistor divider or the internal current source?

When DIR is logic low, is the IPK voltage determined by the 25uA * (R102//R15)? Thanks.

0 Youhao Xi over 5 years ago in reply to Jeff Xie

TI__Guru* 78400 points

The peak current is proportional to the IPK voltage. So, for boost, its IPK voltage should be slightly lower than that of buck mode, in order to keep the same peak current.

Power management

Power management forum

LM5170-Q1: Function of R102