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TPS92691: About higher than 65Vout solution

Satoshi
Guru 19595 points
Part Number: TPS92691
Other Parts Discussed in Thread: TPS92561, , TPS92692

TPS92561 Vout range is 65V_max, but I want to use higher Vout condition. (for example, 110Vout)

I think that operating condition: 65Vout_max is mean the equal to current sense common mode range.

When connect 1/2 divider to CSP/CSN line, common mode range become 1/2 and satisfy the operating condition, is it correct?

Is there the other obstruct for higher Vout condition?

※Example image

Best regards,

Satoshi

  • 0
    TI__Expert 3910 points

    Hi Satoshi-san,

    Your sense signal will be halved in such arrangements.

    Can your system accept low-side current sense, i.e. CSN connects to ground and CSP connects to the LED-?

    I believe low-side current sense is the only way to support VOUT > 65 V with TPS92691.

    Thank you!

  • 0 in reply to Issac Hsu
    Guru 19595 points

    Issac-san

    Thank you for quick reply,

    Low side current sense is OK. (High side current sense is the best)

    Is there application note or reference design for TPS92691(or nearly parts) with low side current sense? 

    Best regards,

    Satoshi

  • 0 in reply to Satoshi
    TI__Expert 3910 points

    Hi Satoshi-san,

    Please refer to the attached diagram for your reference.

    It is a general schematic, therefore, you still need to go through your own calculations on the parametric of passive components.

    The Q2 in the schematic is for PWM dimming for LEDs. If you are not using LED load or do not need PWM dimming, please remove the Q2 and leave DDRV open.

    Thank you!

  • 0 in reply to Issac Hsu
    Guru 19595 points

    Issac-san

    Thank you for kind reply,

    Additional question about low side current sense below, please let me know.

    ①When turn on timing, CSP voltage occur to increase about 110V (steady state is 110V-Vf*LED's).

    　Is low side current sense tolerance voltage change?

    　Are filter value need to change larger than datasheet recommendation? 

    ②Can TPS92692 also use high voltage and low side current sense? 

    　TPS92692 have external slope compensation and need to sense Vout by CSP pin.

    　But CSP voltage is changing depend on ON/OFF timing, LED condition (# of serial, LED's Vf, etc). 

    　I think that difficult to calibrate Vcsp, is there any idea for measure?

    　Or, is SLOPE pin left floating OK? 

    Best regards,

    Satoshi

  • 0 in reply to Satoshi
    TI__Expert 3910 points

    Hi Satoshi-san,

    1. During turn-on, with a correct soft-start setup, the output voltage will not immediately go to 110 V. It takes time and most probably the LED has been turned on in the way and the CSP voltage will have no chance to see the high output voltage. The whole filter network still applies as the CSN in this case does not directly connecting to ground. Instead, CSN connects to ground through RFS. Hence, the whole filter network still work as is.

    2. Does PWM dimming require? If yes, TPS92692 is not suggested for high voltage output as the PWM dimming can only be achieved with an external P-MOS which is driven by CSP voltage. If PWM dimming is not required, then yes, TPS92692 can be considered to be used in low-side current sense configuration. However, we have more customers used TPS92691 low-side sense configuration rather than TPS92692 due to the fact that most of them needs PWM dimming.

    Thank you!

  • 0 in reply to Issac Hsu
    Guru 19595 points

    Issac-san

    Thank you for reply,

    About CSP voltage, is there condition for spec of dimming?

    I think that need to consider CSP voltage spike by PWM dimming (turn-on). 

    Best regards,

    Satoshi

  • 0 in reply to Satoshi
    TI__Mastermind 18890 points

    Hi Satoshi-san,

    I'll answer this for Issac since he's out of the office on travel. 

    The key is not letting CSP or CSN get above the rating voltage specified in the data sheet.  As far as spike by PWM'ing...The TPS92691 or 92 sense the differential voltage across the sense resistor and will also have the differential filter prior to feeding back to the CSP and CSN pin so it will not have any spiking on it.

    Thanks Tuan

  • 0 in reply to Tuan Tran74
    Guru 19595 points

    Tuan-san

    Thank you for reply,

    Sorry for maybe last question, are CSP and CSN voltage not to reach 60V(recommend range) on low side setting?

    Our application is 110~120Vout solution, I'm thinking about whether to connect divider resistance or not (to CSP and CSN).  

    Best regards,

    Satoshi

  • 0 in reply to Satoshi
    TI__Mastermind 18890 points

    Satoshi-san,

    From the schematic that Issac gave you above, you can see that CSN is tied to ground and with current flowing or not the voltage on CSP will be close to ground.  We do not recommend divider resistance since the input current for the sense amplifier will cause a big offset due to the input bias current if you use large resisters values.

    Note that you will still need a filter of two 10 Ohms and 0.1uF for RFS and CFDM.  Please see section 7.3.4 of the data sheet.

    Thanks Tuan