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TPS758: Do we have 3A LDO and VIN need > 7V?

Part Number: TPS758
Other Parts Discussed in Thread: LP3966, , UC3845

Hi Team,

         My customers have choose MIC29302A in their system. They required VIN>7V, Vout=4V and Iout=3A. I found TPS758/LP3966 is pin2pin with MIC29302A.

However, TPS758 VIN max voltage is 5.5V and LP3966 VIN max voltage is 7.5V, which I am not sure if its margin is enough or not. 

So I have some questions:

1. Do we have other suitable sockets to take place to MIC29302A ? Must be Pin2Pin.

2. If we have not other choice, if I promote LP3966 to them, when VIN =7.5v or VIN =7v ,  will LP3966 be damaged? 

BTW, VIN = 7V is from UC3845 flyback output.

Thank for your help!

Eggsy.

  • Hi Eggsy,

    1. Looking at the LDO portfolio on the TI website, there does not appear to be another suitable alternative due to the Pin2Pin requirement.

    2. The maximum recommended VIN for the LP3966 is 7 V. This means the regulator will operate consistently and reliably if VIN is less than or equal to 7 V.  If the UC3845 output voltage exceeds this for an extended time, the LP3966 will not be suitable for the application. However, the maximum output voltage ripple for the UC3845 is 100 mVpp. This means that if configured for a 7 V output, VIN for the LP3966 only varies up to 7.05 V max. In this case the LP3966 is still an option for your customer. The device risks being damaged when the input voltage exceeds the absolute maximum rating of 7.5 V. Again, although it will not get damaged, the maximum input voltage for reliable operation is 7 V.

    Another thing to keep in mind if promoting this device is the thermal performance. The MIC29302A has a juntion-to-ambient thermal resistance (θja) of 28 C/W in the TO-263 package compared to about 60 C/W for the LP3966. If the output current is continuously 3 A, 9 W will be dissipated in the pass FET. Depending on the ambient temperature of your customer's application, the LP3966 may need additional heat sinking through a heat sink or through additional copper area on the PCB. The required θja,max for the application can be calculated from the following equation:

    θja,max = (Tj,max - Ta,max)/Pd

    Tj,max = 125 C - max recommended operating junction temperature

    Ta,max = max ambient temperature

    Pd = power dissipated in the regulator

    After calculating θja,max, Figure 23 of the datasheet can be used to determine how much copper area is needed on the PCB. Alternatively, a heat sink can be attached to reduce θja if PCB changes cannot be made. 

    Thanks,

    Gerard

  • Hi Gerard,

           Thanks for your help!

    It looks like our LP3966 don't have any advantages when competed with MIC29302A.

    Do you have other device or roadmap ?

    Thanks!