SDAA392 July   2026 TPS922050 , TPS922051 , TPS922052 , TPS922053 , TPS922054 , TPS922055 , TPS923650 , TPS923651 , TPS923652 , TPS923653 , TPS923654 , TPS923655

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Precise Dimming Control and Enhanced Dimming Ratio
  6. 3Key Factors for Improved Dimming Performance
    1. 3.1 LED Current Settling Time Reduction and Overshoot Current Suppression
    2. 3.2 LED String Off State Glow Suppression
    3. 3.3 Switching Start Voltage Adjustment
    4. 3.4 Low LED Full Scale Current Improvement
  7. 4Design Guidance for Application Circuit
    1. 4.1 Design of CSP and CSN CFLT and RFLT
    2. 4.2 Design of UVP and OVP Resistors
  8. 5Summary
  9. 6References

3.2 LED String Off State Glow Suppression

Due to leakage paths through SW/CSP/CSN, the LED string may weakly illuminate even when DIM is low. As shown in Figure 3-12, an optional resistor RLK_COMP can be selected to compensate for the CSP+CSN common-mode leakage current and prevent it from flowing through the LEDs. Without RLK_COMP, a leakage path exists when VIN is supplied, there is leakage current path. This leakage path only exists with TPS92205x family which is Buck topology but not Boost and Buck-Boost configuration of TPS92365x family.

Schematic of TPS922051/0 Figure 3-12 Schematic of TPS922051/0

The SW/CSN/CSP leakage current path before and after adding RLK_COMP is shown in Figure 3-13 and Figure 3-14 which shows that the RLK_COMP can help to compensate for the CSP+CSN common mode leakage current and avoid it passing through LEDs.

SW/CSN/CSP leakage path with RLK_COMP Figure 3-13 SW/CSN/CSP leakage path with RLK_COMP
SW/CSN/CSP leakage path without RLK_COMP Figure 3-14 SW/CSN/CSP leakage path without RLK_COMP

To design RLK_COMP, measure the LED voltage and leakage current when VIN is supplied and DIM is pulled down. Then calculate the shunt resistor according to it. For example, the test application is VIN_MAX=54V and 5pcs LEDs. Since the larger VIN, larger leakage current. Thus, considering the worst case which is VIN_MAX, When VIN=54V and DIM is pulled down, ILED is measured as 30.7uA. With 5pcs LEDs, VF is measured as 11.7V. RLK_COMP < 11.7V/30.7uA=381kΩ. It is an effective way to get RLK_COMP.