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AN-CM-275 Automotive Turn Signal with Animation

Contents

Terms and Definitions

ASM Asynchronous state machine
DFF D flip flop
DO Digital output
EN Enable signal
FSM Finite state machine
IC Integrated circuit
IND Indicator signal
LDO Low-drop out
LED Light emitting diode
LUT Look up table
MCU Microcontroller unit
MOSFET Metal-oxide semiconductor field-effect transistor
PCB Printed circuit board
PG Power good
QFN Quad flat no-lead
TSSOP Thin shrink small outline package

References

For related documents and software, please visit:

https://www.dialog-semiconductor.com/configurable-mixed-signal.

Download our free GreenPAK Designer software [1] to open the .gp files [2] and view the proposed circuit design. Use the GreenPAK development tools [3] to freeze the design into your own customized IC in a matter of minutes. Dialog Semiconductor provides a complete library of application notes [4] featuring design examples as well as explanations of features and blocks within the Dialog IC.

  1. GreenPAK Designer Software, Software Download and User Guide, Dialog Semiconductor
  2. AN-CM-xxx Automotive Turn Signal with Animation.gp, GreenPAK Design File, Dialog Semiconductor
  3. GreenPAK Development Tools, GreenPAK Development Tools Webpage, Dialog Semiconductor
  4. GreenPAK Application Notes, GreenPAK Application Notes Webpage, Dialog Semiconductor
  5. SLG46620, Datasheet, Dialog Semiconductor.

Introduction

Recently, animated indicator front and rear LED patterns have become a norm in the automotive industry. These running LED patterns often represent a trademark of the automotive manufacturers and are used for visual aesthetics as well. The animations can be of different running patterns and can be implemented without any MCU using several discrete ICs.

The major requirements of such designs are: reproducible performance during normal operation, an option to force all LEDs on, low power consumption, disabling the used LDO regulator during a fault, loading the LED driver before enabling it etc. Additionally, the requirements can vary from one manufacturer to another. Moreover, usually in automotive applications, TSSOP ICs are usually preferred due to their robustness as compared to QFN ICs since these are known to be prone to solder fatigue issues especially in harsh environments. Fortunately for this automotive application, Dialog Semiconductor provides a suitable GreenPAK IC, namely SLG46620, available in both QFN and TSSOP packages.

All of the requirements for the animated indicator LED patterns are currently met in the automotive industry using discrete ICs. However, the level of flexibility provided by GreenPAK IC is unmatched and can easily cater to varying requirements of several manufacturers without any change in hardware design. Moreover, significant PCB footprint reduction and cost savings are also achieved.

In this app note, a detailed description of achieving different animated indicator light patterns using SLG46620 is presented.

Industry Value

The turn signal patterns shown in this app note are currently implemented in the automobile industry using a number of discrete ICs to control the sequence of automotive indicator LED patterns. The selected GreenPAK IC SLG46620 would replace at least the following components in the current industrial design:

  • 1 No. 555 Timer IC (e.g. TLC555QDRQ1)
  • 1 No. Johnson Counter (e.g. CD4017)
  • 2 No. D-Type Positive-Edge-Triggered Flip-Flop (e.g. 74HC74)
  • 1 No. OR gate (e.g. CAHCT1G32)
  • Several passive components i.e. inductors, capacitors, resistors etc.

Cost Comparison

Table 1 provides the cost advantage obtained by using the selected Dialog GreenPAK IC, for the indicator light sequential turn signal patterns, as compared to a current industrial solution.

Table 1: Cost Comparison
IC Name
Quantity
Unit Price (Ref. Digi-key 23-05-2018) ($)
Price ($)
TLC555QDRQ1
1
0.86
0.86
SN74HC74QDRG4Q1
2
0.58
1.16
CD74HC4017E
1
0.58
0.58
CAHCT1G32QDBVRQ1
1
0.42
0.42
Total Price:
3.02

Note 1    The cost of other auxiliary components (i.e. several resistors, capacitors, inductors) is additional.

The selected GreenPAK IC SLG 46620 would cost less than $0.50, so the total cost of the LED control circuitry decreases significantly. In addition, significant comparative PCB footprint reduction is also achieved.

System Design

Figure 1: Scheme 1 with Single Channel Driver

Figure 1 shows the diagram of the first proposed scheme. The major components of the scheme include a LDO voltage regulator, an automotive LED driver, the GreenPAK IC SLG46620, 11 logic-level MOSFETs and 10 LEDs. The LDO voltage regulator ensures that appropriate voltage is provided to the GreenPAK IC and if the battery voltage drops from a certain level the GreenPAK IC gets reset through the PG (Power Good) pin. During any fault condition, detected by the LED driver, the LDO voltage regulator gets disabled. The SLG46620 IC generates the digital signals to drive the indicator turn LEDs labelled 1-10 through the MOSFETs. Moreover, the selected GreenPAK IC also produces the enable signal for the single channel driver which in turn drives a MOSFET Q1 to load the driver running in constant current mode.

A variant of this scheme is also possible, where a multiple channel driver is employed, as shown in Figure 2. In this option, the driving current of each channel reduces as compared to the single channel driver.

Figure 2: Scheme 2 with Multiple Channel Driver

GreenPak Design

A suitable way to achieve the goal of flexible indicator LED patterns is to use a Finite State Machine (FSM) concept. Dialog semiconductor provides several GreenPAK ICs that contain a built-in ASM block. However, unfortunately all those GreenPAK ICs are available in QFN packages are not recommended for harsh environments. So SLG46620 is chosen which is available in both QFN and TSSOP packaging.

Three examples are presented for three different LED animations. For the first two examples, we consider a single channel driver as shown in Figure 1. For the third example, we assume that multiple channel drivers are available, as shown in Figure 2, and each channel is used to drive a separate LED. Other patterns can also be obtained using the same concept.

In the first example design, LEDs from 1-10 are sequentially turned on one after the other once a certain programmable time period expires as shown in Figure 3.

Figure 3: Example 1 Pattern

In the second example design, 2 LEDs are sequentially added in the pattern as shown in Figure 4.

Figure 4: Example 2 Pattern

Figure 5 depicts how alternate LEDs are sequentially added in the pattern in the third proposed design.

Figure 5: Example 3 Pattern

Since there is no built-in block of ASM available in SLG46620, a Finite State Moore Machine is developed using the available blocks namely counter, DFFs and LUTs. A 16 state Moore Machine is developed using Table 2 for the three examples. In Table 2, all the bits of the present state and the next state are given. Moreover, the bits for all the output signals are also provided. From Table 2 the equations of the next state and all the outputs are evaluated in terms of the present state bits.

Table 2: 16 State Moore Machine for 3 Example Pattern Designs
Indicator
Signal
Present State
ABCD
Next State
ABCD
En
(Ex. 1)
LEDs On
(Ex. 1)
En
(Ex. 2)
LEDs On
(Ex. 2)
En1
(Ex. 3)
En2
(Ex. 3)
LEDs On
(Ex. 3)
0
0000
1111
0
0
0
0
0
0
0
0
0001
1111
0
0
0
0
0
0
0
0
0010
1111
0
0
0
0
0
0
0
0
0011
1111
0
0
0
0
0
0
0
0
0100
1111
0
0
0
0
0
0
0
0
0101
1111
1
1
0
0
1
0
1
0
0110
1111
1
1+2
1
1+2
0
0
0
0
0111
1111
1
1+2+3
0
0
1
0
1+3
0
1000
1111
1
1+2+3+4
1
1+2+3+4
0
0
0
0
1001
1111
1
1+2+3+4+5
0
0
1
0
1+3+5
0
1010
1111
1
1+2+3+4+5+6
1
1+2+3+4+5+6
0
0
0
0
1011
1111
1
1+2+3+4+5+6+7
0
0
0
1
1+3+5+7
0
1100
1111
1
1+2+3+4+5+6+7+8
1
1+2+3+4+5+6+7+8
0
0
0
0
1101
1111
1
1+2+3+4+5+6+7+8+9
0
0
0
1
1+3+5+7+9
0
1110
1111
1
1+2+3+4+5+6+7+8+9+10
1
1+2+3+4+5+6+7+8+9+10
0
0
0
1
0000
0001
0
0
0
0
0
0
0
1
0001
0010
0
0
0
0
0
0
0
1
0010
0011
0
0
0
0
0
0
0
1
0011
0100
0
0
0
0
0
0
0
1
0100
0101
0
0
0
0
0
0
0
1
0101
0110
1
1
0
0
1
0
1
1
0110
0111
1
1+2
1
1+2
0
0
0
1
0111
1000
1
1+2+3
0
0
1
0
1+3
1
1000
1001
1
1+2+3+4
1
1+2+3+4
0
0
0
1
1001
1010
1
1+2+3+4+5
0
0
1
0
1+3+5
1
1010
1011
1
1+2+3+4+5+6
1
1+2+3+4+5+6
0
0
0
1
1011
1100
1
1+2+3+4+5+6+7
0
0
0
1
1+3+5+7
1
1100
1101
1
1+2+3+4+5+6+7+8
1
1+2+3+4+5+6+7+8
0
0
0
1
1101
1110
1
1+2+3+4+5+6+7+8+9
0
0
0
1
1+3+5+7+9
1
1110
0000
1
1+2+3+4+5+6+7+8+9+10
1
1+2+3+4+5+6+7+8+9+10
0
0
0
1
1111
0000
1
1+2+3+4+5+6+7+8+9+10
1
1+2+3+4+5+6+7+8+9+10
1
1
1+2+3+4+5+6+7+8+9+10

Note 2    The first three columns are common for each example

Figure 6: 4-bit Moore State Machine

At the core of the development of 4-bit Moore Machine are 4 DFF blocks. Each DFF block functionally represents one bit of the four bits: ABCD. When the indicator signal is high (corresponding to an on indicator switch), a transition from one state to the next is required at each clock pulse, thus generating different LED patterns as a result. On the other hand, when the indicator signal is low, a stationary pattern, having all the LEDs on in each design example is the goal.

Figure 3 shows the functionality of the developed 4-bit (ABCD) Moore Machine for each example. The basic idea of the development of such FSM is to represent each bit of the next state, the enable signal and each output pin signal (assigned for the LEDs) in terms of the present state. This is where the LUTs contribute. All the 4 bits of present state are fed to different LUTs to basically achieve the required signal in the next state at the edge of a clock pulse. For the clock pulse, a counter is configured to provide a pulse train with a suitable period.

For each example, each bit of the next state is evaluated in terms of the present state using the following equations derived from K-Maps:

A = D' (C' + C (A B)') & IND + IND'

B = C' D + C D' (A B)' & IND + IND'

C = B' C D + B (C' + A' D') & IND + IND'

D = A B' + A' B C D + A B C' & IND + IND'

where IND represents the indicator signal.

Further details of each of the three examples are given below.

Design Example 1

The equations of the enable signal and the LED driving signals for the 1st example, with each LED turning on sequentially using the scheme in Figure 1, are as shown below.

En = A + A' B (C+D)

DO1 = A' B C' D DO2 = A' B C D' DO3 = A' B C D DO4 = A B' C' D'
DO5 = A B' C' D DO6 = A B' C D' DO7 = A B' C D DO8 = A B C' D'
DO9 = A B C' D DO10 = A B C
Figure 7: Example 1 GreenPAK Design Matrix-0

In Figure 7, the Matrix-0 GreenPAK design of Example 1 is shown. 4 DFFs are used to develop the 4-bit Moore Machine. DFFs with reset option (3 from Matrix-0 and 1 from Matrix-1) are selected so that the Moore Machine can be reset conveniently. A counter, with a suitable time period of 72 mS, is configured to change the state of the Machine after each period. LUTs with appropriate configurations are used to derive functions for the DFFs inputs, Driver Enable Signal (En), and the output pins: DO1-DO10.

Figure 8: Example 1 GreenPAK Design Matrix-1

In Matrix shown in Figure 8, the rest of the GreenPAK resources are utilized to complete the design using the methodology described earlier. The figures are appropriately labeled for clarity.

Design Example 2

The equations of the enable signal and the LED driving signals for the 2nd example, with two LEDs adding in the sequential pattern using the scheme in Figure 1, are as shown below.

En = D' (A' B C + A B' C' + A B' C + A B) + A B C

DO1 = 0 DO2 = A' B C D' DO3 = 0 DO4 = A B' C' D'
DO5 = 0 DO6 = A B' C D' DO7 = 0 DO8 = A B C' D'
DO9 = 0 DO10 = A B C

In Figure 9 and Figure 10, the Matrix-0 & 1 GreenPAK designs of Example 2 are presented. The basic design is similar to the Example 1 design. The major differences, in comparison, are in the Driver Enable (En) function and no connections of DO1, DO3, DO5, DO7 and DO10, which are pulled down in this design.

Figure 9: Example 2 GreenPAK Design Matrix-0
Figure 10: Example 2 GreenPAK Design Matrix-1

Design Example 3

The equations of the enable signal and the LED driving signals for the 3rd example, generating alternate LED sequential addition pattern using the scheme in Figure 2, are given below.

En1 = (A' B C' + A B' C' + B C) D

En2 = (A B' C + A B) D
DO1 = D (A+B) DO2 = A B C D DO3 = D (A+ C B) DO4 = A B C D
DO5 = D A DO6 = A B C D DO7 = D A (C' B + C) DO8 = A B C D
DO9 = D A B DO10 = A B C D

In Figure 11 and Figure 12, the Matrix-0 & 1 GreenPAK designs of Example 3 are presented. In this design, there a two separate Driver Enable Signals (En1 & En2) for Driver 1 & 2. Moreover, the output pins are connected to the outputs of appropriately configured LUTs.

This concludes the GreenPAK design part of Example 1, Example 2 and Example 3.

Figure 11: Example 3 GreenPAK Design Matrix-0
Figure 12: Example 3 GreenPAK Design Matrix-1

Experimentation Results

A convenient way to test the designs of Example 1, Example 2 and Example 3 is experimentation and visual inspection. The temporal behavior of each scheme is analyzed using a logic analyzer and the results are presented in this section.

Figure 13 shows the temporal behavior of different output signals for Example 1 whenever the indicator is turned on (IND=1). It can be observed that the signals for the output pins DO1-DO5 sequentially turn on after the other after a set time period expires in accordance with Table 2. The pattern of the signals provided to the pins DO6-DO10 is also similar. The Driver Enable (En) signal turns on when any of the signals DO1-DO10 is turned on and otherwise it is off. During the animation, whenever the indicator signal goes low (IND=0), the En and DO10 signals turn on and remain logical high. In short, the results meet the requirements and validate the theoretical proposals for Example 1.

In Figure 14, the timing diagram of different output signals for Example 2, with the indicator signal turned on (IND=1), is depicted. It is observed that the signals for the output pins DO1-DO5 are turned on alternately in a sequence after some time period in agreement with Table 2. The pins DO1, DO3 and DO5 remain low, whereas the signals for the DO2 and DO4 alternately turn on sequentially. The same patterns for DO6-DO10 are also observed (not shown in the figure due to limited number of analyzer inputs). Whenever any of the signals DO1-DO10 is on, the Driver Enable (En) signal also turns on which otherwise remains off. Throughout the animation, whenever the indicator signal goes low (IND=0), the En and DO10 signals turn on and remain logical high. The results meet the requirements and the theoretical ideas for Example 2 exactly.

Figure 13: Temporal Behavior of Output Signals for Example 1 with IND=1
Figure 14: Temporal Behavior of Output Signals for Example 2 with IND=1
Figure 15: Temporal Behavior of Output Signals for Example 3 with IND=1

Figure 15 shows, the timing diagram of different output signals for Example 3, with the indicator signal turned on (IND=1). It can be observed that the signals for the output pins DO1-DO7 turn on as shown in Table 2. Moreover, pin DO9 signal also behaves according to Table 2 (not shown on figure). Pins DO2, DO4, DO6, DO8, DO10 remain low. The En1 turns logical high whenever a signal from DO1, DO3 and DO5 is on and En2 turns logical high whenever a signal from DO7 and DO9 goes high. During the entire animation, whenever the indicator signal is goes low (IND=0), all the output signals: En1, En2 and DO1-DO10 turn on and remain logical high. Therefore, it can be concluded that the results fulfill the requirements and the theoretical proposals for Example 3.

Conclusion

A detailed description of various automotive turn signal schemes with animation has been presented. A suitable Dialog GreenPAK IC SLG46620 was chosen for this application since it is also available in TSSOP package which is advisable for the harsh environment industrial applications. Two major schemes, using single and multiple channel automotive drivers, are presented to develop flexible sequential LED animation models. Appropriate Finite State Moore Machine models are developed to generate the desired animations. For validation of the developed model, convenient experimentation has been carried out. It is established that the functionality of the developed models agrees with the theoretical design.