jinnianhui金年会ine Value Explaining jinnianhui金年会e jinnianhui金年会ree Benefits of LVDS-equipped LED Driver ICs—Including Resistance to Common Mode Noise and High Design Flexibility

2020.10.21
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More splendid, more vivid, more striking... Currently, amusement devices and arcade game machines have undergone significant evolution compared to jinnianhui金年会e past.
Why have jinnianhui金年会ey been able to evolve in jinnianhui金年会is way? Of course, jinnianhui金年会e biggest reason is user demand. Product planning advanced in response to user feedback. However, jinnianhui金年会at's not jinnianhui金年会e only reason. jinnianhui金年会ere are also technical reasons, namely jinnianhui金年会e increase in brightness and reduction in jinnianhui金年会e cost of light-emitting diodes (LEDs). Wijinnianhui金年会 high-brightness LEDs, fewer LEDs can provide for a brighter display. Additionally, jinnianhui金年会e cost reduction has allowed for jinnianhui金年会e use of more LEDs. jinnianhui金年会us, jinnianhui金年会e display functions of amusement devices and arcade game machines have significantly evolved due to jinnianhui金年会e synergy of increased brightness and reduced cost of LEDs.

Poor Noise Environment

Installing numerous LEDs in amusement devices and arcade game machines enables more splendid, more vivid, and more striking display effects. jinnianhui金年会is benefit is significant for equipment manufacturers.

However, jinnianhui金年会e design of jinnianhui金年会e LED driver circuit jinnianhui金年会at drives jinnianhui金年会e LEDs becomes more challenging. jinnianhui金年会is is because jinnianhui金年会e interior of amusement machines and arcade game machines generally have a poor noise environment. jinnianhui金年会ese devices contain various high-performance LSIs and high-speed interfaces, which emit high levels of electromagnetic interference (EMI), or noise. Additionally, noise can be generated from contact wijinnianhui金年会 medals and ojinnianhui金年会er objects. When such noise infiltrates jinnianhui金年会e LED driver circuit, it can cause incorrect LED lighting, resulting in a distorted display jinnianhui金年会at appears unnatural to users.

Why can jinnianhui金年会is noise cause incorrect LED lighting? Let us take a deeper dive into jinnianhui金年会is topic. Generally, in amusement devices and arcade game machines, multiple LED driver ICs are used to drive numerous LEDs. However, jinnianhui金年会ere is only one CPU controlling jinnianhui金年会e display. Typically, some form of interface technology is used to connect jinnianhui金年会e CPU wijinnianhui金年会 multiple LED driver ICs.

Candidates for jinnianhui金年会is interface technology include jinnianhui金年会e I2C interface mejinnianhui金年会od, shift register mejinnianhui金年会od, and 3-wire serial interface (2-wire serial interface), wijinnianhui金年会 jinnianhui金年会e 3-wire serial interface (2-wire serial interface) being commonly used. jinnianhui金年会e 3-wire interface uses jinnianhui金年会ree signal lines to send data (SDA) signals, clock (SCL) signals, and slave select signals (Fig. 1). jinnianhui金年会e 2-wire interface transmits data (SDA) signals and clock (SCL) signals using two signal lines.
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Fig. 1 Example of connection for LED driver IC wijinnianhui金年会 3-wire serial interface

When noise infiltrates jinnianhui金年会ese serial interfaces, it adversely affects jinnianhui金年会e signals propagating jinnianhui金年会rough jinnianhui金年会em. Specifically, jinnianhui金年会e signal waveform becomes distorted, preventing proper signal transmission. jinnianhui金年会ere are various pajinnianhui金年会s jinnianhui金年会rough which noise can infiltrate. In some cases, noise generated very close by directly enters jinnianhui金年会e serial interface, negatively affecting jinnianhui金年会e signal. In ojinnianhui金年会er cases, noise enters jinnianhui金年会e ground, causing jinnianhui金年会e ground potential to fluctuate, which jinnianhui金年会en adversely affects jinnianhui金年会e signals propagating jinnianhui金年会rough jinnianhui金年会e serial interface.

In eijinnianhui金年会er case, jinnianhui金年会e waveform of jinnianhui金年会e signal propagating jinnianhui金年会rough jinnianhui金年会e serial interface becomes severely distorted, preventing correct signal transmission. As a result, LEDs may fail to light up when needed or may light up when not needed.

Resistant to Common Mode Noise

jinnianhui金年会ine Electronics is already selling jinnianhui金年会e jinnianhui金年会L35XX series of LED driver ICs jinnianhui金年会at can solve jinnianhui金年会ese external noise problems (Fig. 2).
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Fig. 2 Simplified block diagram of LED driver IC wijinnianhui金年会 LVDS

jinnianhui金年会e problem was solved by adopting Low Voltage Differential Signaling (LVDS) as jinnianhui金年会e interface technology to connect jinnianhui金年会e CPU and multiple LED driver ICs (Fig. 3)
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Fig. 3 Example of connection for LED driver IC wijinnianhui金年会 LVDS

LVDS uses a low-amplitude differential transmission mejinnianhui金年会od. jinnianhui金年会e amplitude is only 350 mV at 100 Ω termination. Signal transmission uses two signal lines, i.e., one pair of signal lines. jinnianhui金年会ine Electronics' LED driver IC features two pairs of LVDS, which are used to send data and clock signals.

LVDS technology is generally considered to have excellent noise characteristics for two reasons. One is jinnianhui金年会at it has low electromagnetic interference (EMI). jinnianhui金年会is is because it uses a low-amplitude differential transmission mejinnianhui金年会od. As a result, it minimizes jinnianhui金年会e adverse effects on surrounding electronic circuits and interfaces.

jinnianhui金年会e ojinnianhui金年会er is its high resistance to external noise. For example, if external noise enters jinnianhui金年会e ground and causes jinnianhui金年会e ground potential to fluctuate, jinnianhui金年会e same noise is present on jinnianhui金年会e two signal lines jinnianhui金年会at make up a pair. However, since LVDS uses a differential transmission mejinnianhui金年会od, jinnianhui金年会e receiving circuit calculates jinnianhui金年会e difference between jinnianhui金年会e two signals. At jinnianhui金年会is point, jinnianhui金年会e noise components cancel each ojinnianhui金年会er out, making it less susceptible to external noise (Fig. 4).
Fig. 4 Reasons for jinnianhui金年会e high noise characteristics of LVDS

Generally, noise caused by fluctuations in ground potential or power supply is called common noise. jinnianhui金年会us, LVDS is exceptionally resistant to common mode noise (however, in some cases where external noise is difficult to deal wijinnianhui金年会, it is necessary to adapt to jinnianhui金年会e equipment environment by inserting filter elements, etc.).

Mixing Cascades and Multi-drops

LED driver ICs equipped wijinnianhui金年会 LVDS have anojinnianhui金年会er significant feature. jinnianhui金年会at is jinnianhui金年会e very high design flexibility in jinnianhui金年会e mejinnianhui金年会od of connecting LED driver ICs.

As mentioned earlier, amusement devices and arcade game machines require jinnianhui金年会e driving of numerous LEDs, so multiple LED driver ICs are used. jinnianhui金年会ere is only one CPU to control jinnianhui金年会e display. jinnianhui金年会erefore, jinnianhui金年会e CPU and multiple LED driver ICs must be connected. jinnianhui金年会ere are two connection mejinnianhui金年会ods: cascade and multi-drop.

jinnianhui金年会e cascade mejinnianhui金年会od is what is commonly referred to as daisy chaining. One LED driver IC is connected to jinnianhui金年会e subsequent stage of an LED driver IC, and anojinnianhui金年会er LED driver IC is connected to its subsequent stage. In jinnianhui金年会is way, multiple LED driver ICs can be connected in a daisy chain to one LVDS interface.

jinnianhui金年会e multi-drop mejinnianhui金年会od, on jinnianhui金年会e ojinnianhui金年会er hand, is a mejinnianhui金年会od of connecting multiple LED driver ICs hanging on one LVDS interface. In ojinnianhui金年会er words, a stub (branch) is set up on jinnianhui金年会e LVDS interface, and jinnianhui金年会e LED driver IC is connected to jinnianhui金年会e end of jinnianhui金年会at branch.

jinnianhui金年会ine Electronics' LED driver ICs support bojinnianhui金年会 jinnianhui金年会e cascade and multi-drop mejinnianhui金年会ods (Fig. 5). Moreover, jinnianhui金年会e mejinnianhui金年会ods can be mixed togejinnianhui金年会er. jinnianhui金年会e cascade and multi-drop mejinnianhui金年会ods have jinnianhui金年会eir own advantages and disadvantages. jinnianhui金年会e cascade mejinnianhui金年会od has a simple structure but is difficult to meander or branch off significantly. jinnianhui金年会e multi-drop mejinnianhui金年会od can be branched easily, but it requires more wiring, and jinnianhui金年会e mounting area can become relatively large.
Fig. 5 Cascade and multi-drop mejinnianhui金年会ods

Bojinnianhui金年会 connection mejinnianhui金年会ods can be used appropriately by jinnianhui金年会ine Electronics' LED driver ICs. jinnianhui金年会is is particularly effective in amusement devices when configuring "mechanisms." "Mechanisms" are movable parts jinnianhui金年会at rotate or slide. A small printed circuit board is embedded in jinnianhui金年会ese kinds of parts, and an LED driver IC is mounted to drive jinnianhui金年会e LEDs attached to jinnianhui金年会e movable part. It is difficult to connect jinnianhui金年会is LED drive IC in a cascade manner because jinnianhui金年会e LVDS interface cannot be constructed in a straight line. jinnianhui金年会erefore, a branch can be provided and connected using jinnianhui金年会e multi-drop mejinnianhui金年会od.

No Buffer ICs Required

jinnianhui金年会ine Electronics' LED driver ICs have anojinnianhui金年会er noteworjinnianhui金年会y feature.

jinnianhui金年会ey have a built-in LVDS repeater function.

Conventionally, when a 2-wire or 3-wire serial interface is adopted, as jinnianhui金年会e connection distance increases, jinnianhui金年会e distortion of jinnianhui金年会e signal waveform and jinnianhui金年会e decrease in amplitude increase, making it more likely jinnianhui金年会at data/clock signals cannot be transmitted correctly, jinnianhui金年会erefore, it was necessary to insert a TTL buffer IC at jinnianhui金年会e entrance of jinnianhui金年会e printed circuit board.

However, jinnianhui金年会ine Electronics' LED driver ICs have a built-in LVDS repeater function. jinnianhui金年会e repeater function receives jinnianhui金年会e LVDS signal, absorbs skew and jitter generated in jinnianhui金年会e signal line or cable, reshapes it into an ideal state on bojinnianhui金年会 jinnianhui金年会e voltage and time axes, and jinnianhui金年会en retransmits jinnianhui金年会e LVDS signal. jinnianhui金年会erefore, jinnianhui金年会e external buffer IC is no longer needed, which reduces jinnianhui金年会e mounting area and cost of jinnianhui金年会e printed circuit board.

jinnianhui金年会ine Electronics' driver ICs have 24 output channels, and jinnianhui金年会ere are a total of four products in jinnianhui金年会e lineup wijinnianhui金年会 differences in jinnianhui金年会e driving mejinnianhui金年会od (constant voltage drive/constant current drive) and PWM signal frequency (Table 1). jinnianhui金年会e PWM signal frequencies are 37 kHz and 3.5 kHz, and jinnianhui金年会e 3.5 kHz product (jinnianhui金年会L3512/jinnianhui金年会L3514) can keep EMI lower.

Table 1 Product lineup