DLPS039F December 2015 – April 2019 TPS99000-Q1
The TPS99000-Q1 provides an output signal, CMODE, that can be used to drive the gate of a FET that switches in a larger capacitor for discontinuous operation. High capacitance mode is only used during discontinuous operation. (High capacitance causes issues in continuous operation, minimizing capacitance is preferred for that mode). The higher capacitance slows the rate at which the forward voltage of the LED increases during the pulse creation process. The slower charge rate causes the transition from no light emission to full light emission to extend in time. In selecting the proper capacitance, a balance between good edge rate control and total time for pulse to reach threshold must be made. Attention should be paid to the temperature characteristics of this capacitor. Less variation of capacitance over temperature will result in more accurate, repeatable results in cold/hot conditions.
The charge and discharge loops using the CMODE big cap are as follows: