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TPS92515-Q1: schematic review

Sherry Liang
Genius 10255 points
Part Number: TPS92515-Q1
Other Parts Discussed in Thread: TPS92515

Dear team,

1. Could you please help review below schematic? Because the customer wants to make the PCB's size smaller, could you please help optimize the schematic?

2. When the Vin=7V, Iout=1A, can the Vout reach 6.4V?

3. In the datasheet, the absolute maximum rating of COFF is 5.5V. Now the COFF connect a resistor from the Vout, and the Vout is 6.4V which exceeds 5.5V. Will this pin be damaged?

4. How to change the Fsw?  Can I choose a higher frequency (more than 2MHz)?

Thanks & Best Regards,

Sherry

  • 0
    TI__Mastermind 28655 points

    Hello Sherry,

    1)  The size will depend on the components chosen.  The inductor is one of the larger parts, it needs to be big enough to handle the current without saturating or getting too hot.

    2)  Yes it can, provided the parts chosen and layout do not cause significant voltage drops.  Depending on the current ripple it may start to appear that the average current start increasing when Vin gets close to Vled.  The TPS92515 can run to 100% duty but does need to refresh the boot capacitor when it hits Boot UVLO.

    3)  The Coff pin allows the voltage on the pin to rise to 1.0V as Coff charges, then the TPS92515 discharges the Coff capacitor, this is how the off-time is set.  by design the Coff pin will be pulled to the LED voltage through a resistor and not damage the TPS92515.

    4)  The switching frequency is set by the off-time, Vin and Vled (or duty cycle).  At 50% duty cycle the off-time and on-time are the same.  If the off time is 400 ns, the switching frequency would be 1/(offtime + ontime), in this case 1/(400ns + 400ns).  What is your Vin and Vled range?  Your Toff calculates to 375 ns.  Ton will be longer when Vin = 7V and Vled = 6.4V, I calculate 4 us (not including the current sense voltage drop or any other voltage drops), however it will be operating in an area where the frequency will vary a lot.  It is not recommended to run higher than 2 MHz.  To change the frequency requires going through the calculations to determine toff and ton (at all operating conditions).  Roff, Coff and Vled set the off-time.  This is described in the datasheet.

    Best Regards,

  • 0 in reply to Irwin Nederbragt
    TI__Mastermind 28655 points

    Hello Sherry,

    I haven’t heard back from you, I’m assuming you were able to resolve your issue.
    If not, just post a reply below (or create a new thread if the thread has locked due to time-out)

    Best Regards,