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TPS92511

SNVS901A – MARCH 2014 – REVISED MAY 2014

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7.3 Feature Description

7.3.1 Pulse Level Modulation (PLM) Control

A proprietary Pulse-Level-Modulation (PLM) control method is used in the TPS92511.

It can regulate the

average LED current by sensing only the inductor current at the on-period (Figure 13). The integrated MOSFET

and the sensing and control circuits in the TPS92511 implement the whole PLM control internally so the control

does not suffer from tolerance and noise issues that may be coming from external components. As compared

with the conventional method which regulates average LED current by sensing the current over the entire

switching cycle, the power dissipation on the sensing circuit in PLM is much lower. For example, consider a duty

cycle of 0.5, the power dissipation on current sensing in PLM can be reduced by half. PLM requires no external

loop compensation circuit. Besides, the accuracy of the regulated LED current is high (typically ±3.5% in the

TPS92511).

Figure 13. Waveforms of a Floating Buck LED Driver with PLM

7.3.2 Pulse Level Modulation (PLM) Operaion Principles

The Pulse-Level-Modulation is a patented method to ensure an accurate average output current regulation

without the need of direct output current sensing. Figure 13 shows the current waveforms of a typical buck

reference level, PLM achieves LED current regulation by sensing the main MOSFET current solely, instead of

7.3.3

PLM Control enable Common-Anode Low-Side Sensing (CALS)Technique to Save Wiring

For multi-channel systems with separated driver boards and LED array boards, the Pulse-Level-Modulation

(PLM) control scheme enable Common-Anode Low-Side Current Sensing to save inter-board wirings. Figure 14

shows a conventional configuration with a Low-side switching and High-Side Current Sensing. For an n channel

system with separated driver and an LED array boards, 2n inter-board wirings are required. For example, an

128-channel system needs 256 inter-board wirings, which implies a high material and manufacturing cost.

Figure 15 shows the PLM configuration with Low-side switching and Low-Side Current Sensing. A Common-

Anode configuration is used for the LED array board. As shown in the figure, an n channel system with separated

driver and LED array boards requires only n+1 inter-board wirings. For an 128-channel system, only 129 inter-

board wirings are required. The wiring cost is cut by half, and the cost of the end product can be reduced.

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