TPS922052: TPS922052 – Shunt Resistor + UVP Divider Dimensioning

Alexander Wagner

Part Number: TPS922052

Tool/software:

Hi,

we're using the TPS922052 in an LED driver. We had an issue with the LEDs glowing when turned off, which we resolved by adding a high-ohmic shunt resistor(as suggested in this forum).

Now we're trying to tune the UVP/UVLO divider so that the voltage drops below 1 V in an open-load condition to trigger a shutdown.

We can achieve that, but then during normal operation, the UVLO pin voltage also stays below 1.4 V, which seems too low for reliable operation.

Question:

Is there a formula or rule of thumb to properly size the UVLO/UVP divider so that:

open-load < 1 V, and
normal operation > 1.4 V?
no glowing in turn off mode

Thanks!
Alexander

1 month ago

0 Lucia Gao 1 month ago

TI__Mastermind 30291 points

Hi Alexander,

Pls kindly refer to below link:

[FAQ] How to design the UVP resistor divider for TPS922055 / TPS922054 / TPS922053 / TPS922052?

Thank you!

BRs

Lucia

0 Alexander Wagner 1 month ago in reply to Lucia Gao

Prodigy 10 points

Yes, I am aware of this FAQ article. However, it refers to another post where it is recommended to use a shunt resistor (e.g., 390k) to prevent the residual glow. In that example, the voltage divider UVP1/UVP2 is also set to a very high resistance, in the range of 1–2 MΩ.

However, with the shunt resistor in place, it is not possible to set UVP so that open load is reliably detected while at the same time ensuring that the 1.4 V threshold is safely maintained during normal operation. In order for UVP2 to drop below 1 V when using the shunt resistor, UVP2 needs to become extremely small—which in turn means that the operating voltage can no longer reliably stay above 1.4 V. This makes the configuration problematic for normal operation.

0 Lucia Gao 1 month ago in reply to Alexander Wagner

TI__Mastermind 30291 points

Hi Alexander,

Pls kindly let me clarify, just as the E2E thread explained, there are two ways in order not to make LEDs slightly glowing when it's in OFF state because of leakage current.

Use UVP resistor divider with a larger value.
Parallel a large resistor R_shunt (may in hundreds of kohm) with LED string and shunt the leakage current. Actually, the R_shunt, R4 and R6 act like a voltage divider when the IC is disabled, where you should set the voltage across the LED string less than the voltage that will light up the LED. An illustration graph is shown below.

You can just try first way and use UVP resistor divider with larger value just like below thread explained:

e2e.ti.com/.../faq-how-to-design-the-uvp-resistor-divider-for-tps922055-tps922054-tps922053-tps922052

Thank you!

BRs

Lucia

0 Alexander Wagner 1 month ago in reply to Lucia Gao

Prodigy 10 points

Thank you for the clarification!
It now also works for me with a total resistance of the voltage divider of 5–6 MΩ without a shunt resistor. The LEDs fade out after switching off, but that’s just due to the very low current and the output capacitance.

Thanks again for your help and the clear explanation!

0 Lucia Gao 1 month ago in reply to Alexander Wagner

TI__Mastermind 30291 points

Hi Alexander,

Your welcome. Have a nice day!

BRs

Lucia

Power management

Power management forum

TPS922052: TPS922052 – Shunt Resistor + UVP Divider Dimensioning

Question:

[FAQ] How to design the UVP resistor divider for TPS922055 / TPS922054 / TPS922053 / TPS922052?