This applicaTIon note discusses how to "Charlieplex" a display driver circuit to reduce pin-count. This unusual mulTIplex technique is used by the MAX6950, MAX6951, MAX6954, MAX6955, MAX6958, and MAX6959 LED display drivers. Charlieplexing reduces driver pin-count by using some pins alternately as cathode and anode drivers. This differs from the standard LED multiplex connection, which uses separate driver pins for anodes and cathodes.
The standard connection for multiplexing common cathode (CC) LED digits uses a separate pin for each digit's CC connection, while the anode segment connections are communed across all the digits. Similarly, the standard connection for multiplexing common anode (CA) LED digits uses a separate pin for each digit's CA connection, while the cathode segment connections are communed across all the digits. The number of connections required can be calculated as being 1 for every digit used, plus 1 for every segment within a digit. Therefore an 8-digit, 8-segment multiplex driver typified by the MAX7219 and MAX7221 CC drivers uses 8 cathode drive pins and 8 anode drive pins, 16 drive outputs in total (Figure 1).
For Larger Image
Figure 1. The MAX7219 and MAX7221 use standard connections - 16 pins to drive 8 digits.
A more pin-efficient scheme relies on the fact that during the multiplex operation, only one CC or CA digit drive output is actually in use. The other digit drives are high-impedance, ensuring that no drive current flows into these undriven digits. By making the LED drive pins alternate duty between driving digits and segments, n drive pins can be used to drive n digits each with n-1 segments. Charlie Allen originally championed this technique internally at Maxim, and so the shorthand name "Charlieplexing" came into use to distinguish reduced pin count multiplexing from the traditional method. The first Maxim product to use Charlieplexing is the Maxim MAX6951 LED driver, which drives 8 numeric digits with only 9 pins (Figure 2).
For Larger Image
Figure 2. The MAX6951 uses Charlieplexing - only 9 pins to drive 8 digits.
To understand how Charlieplexing works, first examine the pin connections shown in Table 1. There is one row per multiplexed digit, and each row contains 9 columns. For each digit, one column corresponds to the CC digit drive, and the remaining 8 columns correspond to the 8 anode (segment) drives.
Table 1. The MAX6951 Driver to LED Display Connections
Pin 6
Pin 5
Pin 4
Pin 3
Pin 14
Pin 13
Pin 12
相关文章
- 网约车经营暂行管理办法总则全文 十一月一日起正式实施
- 深圳巴士集团在新能源汽车推广上走过八年,目前终于实现了出租车100%电动化
- 2017新能源汽车排行榜_新能源汽车哪款好(2017)
- 用一根导线传递联络信号的电路图
- 浙江大学研发盲人视觉辅助眼镜
- 基于加速度测量传感器实现高精度惯性测量组件系统的应用方案
- 位移传感器你真的懂?选型及常见故障排除方法介绍
- 丰田奔跑者,这款进口越野车不到30万,品质不输路虎揽胜!
- 2025年汽车光电市场规模有望达到98.0亿美元
- 关于音箱的技术测试和主观音质的评价
- Cirrus Logic数字音视频处理器、模拟及混合信号IC
- BOS 21M ADCAP多功能光电传感器有哪三种独特高阶性能?