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Original question:

LM5170EVM-BIDIR: when use buck mode, input voltage is 48V, but the output is not 12V

LM5170EVM-BIDIR: LM5170EVM

Vishnu Maheswar
Prodigy 70 points
Part Number: LM5170EVM-BIDIR
Other Parts Discussed in Thread: LM5170, LM6142

Hi,

We are using LM5170 EVM as 12 V Lead Acid battery charger. (48 V i/p, 14.5 V o/p)

We need to set the current limit as 60 A and keep the voltage regulated around 14.5 V.

We rely on the analog voltage loop to set the voltage at 14.5 V (keeping the EVM resistor values as such).

When we use the analog voltage loop, we observe that we cant load more than 25 A, as it sets the ISETA pin voltage at 0.66 V.

I think it is supposed to work in the same way, as the U2B (LM6142 opamp) output clamps to 2.048 V (U13 REF voltage) and limiting the ISETA voltage around 0.66 V (corresponding to 25 A).

Please suggest the ideal solution from your side to operate the EVM to regulate the voltage around 14.5 V and setting the current limit to 60 A.

Waiting for your response.

Thanks in advance,

Vishnu Maheswar

  • 0
    TI__Guru* 78190 points

    Hi Vishnu,

    Thank you for using the LM5170.  The EVM set the current limit to about 64A, not 25A.  The output of LM6142 should be as high as close to 5V.  I don't understand why you said is is clamped by U13. 

    It is the resistor divider consisting of R86 and R81 that clamps the max ISETA voltage, and thereby limiting the max dc current at the buck output.  The 5V from the op-amp minus the diode drop of D9  or D8 is the max voltage seen by the resistor divider, which is close to 4.5V.   If you want to lower the current limit you may reduce R86 slightly. 

    Hope this clarifies.

    Thanks,

    Youhao Xi, Applications Engineering