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ASL5015FHN 数据表(PDF) 27 Page - NXP Semiconductors |
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ASL5015FHN 数据表(HTML) 27 Page - NXP Semiconductors |
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27 / 69 page  NXP Semiconductors ASL5xxxyHz Matrix LED Controller (MLC) ASL5xxxyHz All information provided in this document is subject to legal disclaimers. © NXP B.V. 2019. All rights reserved. Product data sheet Rev. 2.1 — 5 February 2019 27 / 69 8.8 Charge Pump The charge pump mechanism integrated in the ASL5xxxyHz family is able to detect the maximum LED string voltage to have a voltage always at least 5 V higher than the maximum detected LED string voltage. This action allows the internal charge pump circuit to drive all the switches of the MLC without any problem and in a safe way. This intelligent charge pump controls all the blocks, even when they are driving different LED strings with different configurations. The charge pump only requires one external small capacitor. The multiplexer that is connected to the highest switches in every floating block is responsible for detecting the maximum voltage of the LED string. With this mechanism, the Matrix LED Controller (MLC), is able to detect the maximum voltage in the blocks even when they are controlling different LED strings. The charge pump mechanism needs an external capacitor. The external capacitor value selections are described in Table 20. Table 20. External charge pump capacitor selection N° of switches in parallel Minimum capacitor Comments — 4.7 nF / 16 V / X7R No blocks in parallel 2 10 nF / 16 V / X7R 2 blocks in parallel 3 15 nF / 16 V / X7R 3 blocks in parallel 4 22 nF / 16 V / X7R 4 blocks in parallel The selection criteria are based on the current and gate charge required to close the switches safely. When blocks are parallel, more current is required to act in more switches at the same time, for that reason the charge pump capacitor has a greater value. The maximum allowed capacitor value in the CP pin is 68 nF, because a higher value can affect the IC startup time and may produce a CPFAIL status. A 220 pF capacitor should be connected between the VMAX pin and ground (100 V capacitor) to reduce the charge pump ripple and the electromagnetic emissions. The capacitor con also be connected between VMAX pin and SW15 pin (16 V capacitor) See Figure 6. 8.9 Charge pump fail-safe operation mode (CPFSO) In case of failure in the internal charge pump circuit or external charge pump capacitor, the Matrix LED Controller (MLC) enters in a fail-safe operation mode (CPFSO) to provide the maximum operability as possible. If the charge pump fails, the MLC is not able to drive the following: • Top switch of the top block, in case of driving LED segment. • First two switches of the top block, in case of driving single LED per switch. The charge pump fail-safe operation mode starts when the MLC detects a problem in the charge pump. Depending on the open circuit threshold programmed in the MTP, it opens (high ohmic state) the first switch of the top block (OC = 1) or the first two switches of the top block (OC = 0). |
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