# TPS61197 IC issues for outer LED driver circuit

In this setup, we've employed the TPS61197 IC to boost the voltage for both the inner and outer LED rings. The inner ring LEDs require separate brightness control from the outer ring LEDs. The inner ring comprises 18 LEDs, while the outer ring has 34 LEDs.

For the inner ring, the total series LED voltage is approximately 3V x 18 = 54V. Each LED can draw up to 200 mA of current, resulting in a total LED string current of 200 mA. To achieve this, we need a step-up LED driver capable of delivering 54V/200 mA from a 12-24 volts power source.

For the outer ring, the total series LED voltage is approximately 3V x 34 = 102V. Similarly, each LED can draw up to 200 mA of current, leading to a total LED string current of 200 mA. To power this, we also require a step-up LED driver capable of supplying 102V/200 mA from a 12-24 volts power source.

The inner LED driver circuit is functioning perfectly, as demonstrated in the video. However, the outer LEDs' driver circuit encounters an issue—it boosts the voltage but briefly turns on the LEDs and then turns them off immediately.

There appears to be an issue with the outer LEDs' driver circuit.

Here is the link to the video: Google Drive

• Could you attach a schematic of your design, or at least the section in question? Since you already have a full PCB fab did you have a working prototype?
– Nedd
Sep 20 at 7:40
• Are you monitoring the Fault pin? Per the data sheet this will be low during normal operation, then go to a Hi-Z state during a fault condition. An LED with a resistor to Vin could monitor this. Have you reviewed the possible Fault Conditions listed in Table 3 (p16) ?
– Nedd
Sep 20 at 8:00
• Sep 20 at 11:08

As in the answer from Velvel, the series string of C45, C75, C84, C85, C86 and C87 are all connected incorrectly. The reason your LEDs flash briefly is because the current flows only for the short time while the caps charge up. I can only assume that you used all these caps in series because of the high voltage involved. Is that correct?

If the total summed up voltage ratings of these 6 caps exceed the expected high voltage then there is a moderately easy set of corrections you can make.

1: Completely remove the far right pin of C87 from the board, connect it directly to GND*.

2: Connect the D57,C45 point to the "Vout Outer Ring",R11 point.
.

*Read the recommendations in the datasheet at section 10.1 "Layout Guidelines", especially as related to EC2, which in your case is the string of 220uF capacitor(s).

During testing you'd be best advised to wear safety glasses, if an electrolytic cap is inverted or over stressed (by high voltage) it could explode. Also, be sure to keep your hands well away from any open high voltage connections.

Be sure that over voltage components on the OVP pin have been correctly calculated. For added circuit protection you might later think about placing an over voltage component or an additional protection circuit at the D57-C45 point.

• #Nedd #Velvel "Thank you for your help now and in the future. Your assistance is greatly appreciated. Sep 21 at 15:12

The TPS61197 is a current mode boost controller.

From a first glance the design of the inner LED ring seems sane:

But I have no idea what the outer LED ring is supposed to do:

The capacitors C45, C75, C84, C85, C86 and C87 don't allow a constant current to flow. You need to design this similarly to the inner LED ring (C35, C7).

Just make sure that COUT doesn't exceed 200 µF.