TPS923653: Considering TPS923653 for wide input buck/boost application 12-48VIN 1.4A 18.5VOUT max

Hi Michael,

Michael Brust1 said:

• VIN_MIN: 12V
• VIN_MAX:48V
• WLED Vf max of 18.5V
• Iled_max: 1.4A
• Analog dimming input.

Based on your spec requirements, TPS923655 buck-boost connection does not fit here as when Vin = 48V and Vf = 18.5V, the CSP / CSN / SW pin will see a voltage of 48V + 18.5V = 66.5V, which is out of the Recommended Operating Conditions of the IC. Please refer to Section 7.3 Recommended Operating Conditions from the datasheet.

I would recommend you first use a pre-boost stage to boost the input voltage to a middle voltage, like 52V, and then use a buck LED driver like TPS922052 / TPS922053 to drive the LEDs.

Best Regards,

Steven

Hi Steven,

Thanks for the reply. Does TI have any other buck/boost options here that would work? Or is the only architecture you describe the only path with TI parts?

Thanks again,

-Mike

Hi Michael,

I will check with other teams and will reply to you next Monday.

Best Regards,

Steven

Hi Michael,

I have checked this point with other teams. The architecture I described above is the only path if you want to use a TI LED driver (integrated constant-current driver). 

However, I think it is possible to do this with a normal constant-voltage buck-boost controller like LM5177 (I just list this part number here as an example since I am not quite familiar with those parts and I just did a rough search. So it may not fit.) with some external circuit to modify it from constant-voltage control to constant-current control. You can raise a new E2E question regarding those buck-boost controllers and see if the engineers responsible for these parts have any idea.

Best Regards,

Steven

Hi Steven,

After looking around at our options I think we will pursue the LM5176 as an input regulation stage to provide 12V for our LED drivers.

I am considering the TPS923653- is there anything else to be aware of using this part in boost configuration from a 12V input? Are there any major differences between the different packages and current limits? It seems the VSON package has the best thermal performance so I think we'll use that one. We'd like the spread spectrum feature as well.

Is it possible to get the Altium CAD for the EVK for this part? It would be a big help!

Thanks,

-Mike 

Hi Michael,

I am currently out of office. I will reply to you tomorrow. Thanks for your understanding.

Best Regards,

Steven

Hi Michael,

• You should use TPS923655 instead for Vin = 12V, Vout = 18.5V and Iout = 1.4A condition. The current limit of TPS923653 is too small for your application condition.
• Please also make sure your LED will not light up when Vf = 12V. (There is a possible current leakage from Vin, inductor, Schottky diode, sense resistor, LED and then to GND in boost topology.)
• VSON package has the smallest junction-to-ambient thermal resistance.
• The schematics and PCB layout of the EVM is shown in the EVM User's Guide.

Best Regards,

Steven

Hi Steven,

Thanks for the reply. I will use TPS923655. Our Vf_nominal is 16.5v so I think we should be OK at Vin = 12v.

Could you review the schematic for any issues?

Thanks,

-Mike

Hi Michael,

Please refer to my comments below:

• Using an 18.2A-rating inductor and a 12-A Schottky diode is over spec for your application condition. You can choose those with smaller current rating.
• I recommend you use larger-inductance inductor or use higher switching frequency. I would recommend you choose a K_IND < 60% (Please refer to Section 9.2.1.2.1 Inductor Selection from the datasheet.). 
• You need another larger capacitor C_SENSE across the sense resistor (Please refer to Section 9.2.1.2.5 Other External Components Selection from the datasheet).
• You choose the wrong voltage divider for OVP pin. Please refer to this [FAQ] on how to design the OVP resistor divider.
• C51 is too large and is not needed. Please refer to this [FAQ] on how to design the COMP pin components.

Best Regards,

Steven

Hi Steven,

Thanks for the thorough review. I made the requested changes. I changed the inductor to 15uh / K_IND to be 35%. Thanks!

Hi Michael,

I am currently out of office. I will reply to you tomorrow. Thanks for your understanding.

Best Regards,

Steven

Hi Michael,

Please refer to my comments below:

• I would recommend you leave a footprint for R_DAMP in your design (Please refer to this [FAQ]).
• You still do not design the OVP resistor divider correctly (Please refer to this [FAQ]). You current setting gives (1000/78.7 + 1) * 1.1V = 15.08V and this value is lower than your LED voltage (18.5V). You should make sure this value is higher than your maximum LED voltage if you do not want the output current to be affected by the CV mode.

Best Regards,

Steven