A 5-100V Input Low-Profile Adaptive Delay Compensated Hysteretic LED Driver with Enhanced Current Accuracy

Nowadays, miniaturized DC-DC LED drivers that can support 10s of output LEDs are essential in different high-brightness LED lighting systems. Instead of multiple LED strings [1],[2], driving a single LED string avoids the current mismatch issue, but it incurs challenges in the design of the LED driver to simultaneously achieve high power efficiency, low profile via using small inductance, and high current accuracy. For power efficiency consideration, previous hard-switching (HS) HV LED drivers operate at a relatively low switching frequency $(\mathrm{F}\mathrm{s}\mathrm{w})$ of 100s-of-kHz to limit its switching power loss, thereby using large-value inductors of $\geq 47\mu \mathrm{H}[3],$ [4]. Although the soft-switching (SS) LED driver was repoited to minimize the switching power loss [5], it adopts a traditional hysteretic current controller (HCC) to regulate the average LED current. Specifically, the circuit delays (TDH and TDL) for controlling high- and low-side power FETs MH and ML shown in Fig. 1 would result in unequal peak and valley current deviations ($\Delta 1_{\mathrm{L},\mathrm{E}\mathrm{P}\mathrm{K}}$ and $\Delta 1_{\mathrm{L},\mathrm{E}\mathrm{V}\mathrm{Y}}$) and thus the LED current error $(\Delta 1_{\mathrm{L}\{\mathrm{E}\mathrm{R}\mathrm{R}\}})$, when regulating both peak and valley sensed inductor currents. In case the inductor current slopes (SH $\varepsilon_{\mathrm{t}}$ SL) increase due to higher input and output voltages, and both delays TDH and TDL occupy a larger portion at a higher frequency $\mathrm{F}\mathrm{s}\mathrm{w}($where a smaller-value inductor is used), $\Delta 1_{\mathrm{L}(\mathrm{E}\mathrm{R}\mathrm{R})}$ would be significantly increased. Hence, $\Delta 1_{\mathrm{L}(\mathrm{E}\mathrm{R}\mathrm{R})}$ in [5] is ± 25% of a nominal $350\mathrm{m}\mathrm{A}$ LED current with a $10\mu \mathrm{H}$ inductor and 1. $6\mathrm{M}\mathrm{H}\mathrm{z}$ maximum $\mathrm{F}\mathrm{s}\mathrm{w}$.