Hi TI,
The TPS92200 datasheet stated that the Inductor current ripple >300mA requirement, even smaller inductor value is required in order to meet the high inductor current ripple to assure loop stability.
What if I set the ILED max to 300mA and below by using very low duty cycle? It means the current ripple ratio is >50% and inductor occur discontinuous conduction mode, thus efficiency and power loss should be in bad performance. Please advice.
Thanks and regards,
ZL Woon
Hi ZL,
When the I_LED is very low, the TPS92200 will not enter discontinuous mode. Instead, the low-side MOSFET will keep turning on in the cycle to maintain a continuous conduction, unless the sinking current exceeds the I_LIM_LS_SINK. (Please refer to the Section 7.3.7.3 Low-Side MOSFET Sinking Overcurrent Protection from the datasheet)
Though the efficiency may be lower at low-current condition due to low-side MOSFET conduction loss, the analog dimming linearity is better in such a continuous way.
Below is a screen capture from the 6.5 Electrical Characteristics from the datasheet.
BR,
Steven
Hi Steven,
In case my duty cycle is dynamic change during operation, which is from 10% to 90%.
Let say,
The inductor current ripple ratio will be 188% during duty cycle = 10% ,
The inductor current ripple ratio will be 21% during duty cycle = 90% ,
What is the lower/upper limit or maximum/minimum inductor current ripple ratio to prevent loop stability issue?
Based on previous product evaluation, the TPS92200 will have stability issue when inductor current goes to negative. Thus, the lower limit is only 13% duty cycle since >300mA inductor current ripple is a strongly request by TPS92200.
But why it is >300mA instead of 30%? Please advice.
Thanks and regards,
ZL Woon
