ST STLED325 User Manual
I²C interfaced, advanced LED controller/driver with keyscan,
standby power management and real time clock (RTC)
Features
■ LED controller driver with 13 outputs
(8 segments/5 digits)
■ Standby power management to host
■ Integrated low-power, accurate RTC
■ Integrated remote control decoding:
– Philips (RC5, RCMM)
– Thomson (RCA, R2000)
– NEC and R-STEP
■ Wake-up using front panel keys, remote
control, real time clock (RTC), extra pin (AV or
CEC)
■ Battery or super-cap back up mode for real
time clock (RTC)
■ Keyscanning (8x2 matrix)
■ Low power consumption in standby mode
2
■ I
C serial bus interface (SCL, SDA)
■ 16-step dimming circuit to control the display
brightness
■ 5.0 V (± 10%) for V
■
Built-in thermal protection circuit
■ External crystal with internal oscillator for real
time clock (RTC)
Applications
■ Set-top boxes
■ White goods
■ Home appliances
■ DVD players, VCRs, DVD-R
CC
STLED325
QFN32
(5 x 5 mm)
Description
The STLED325 is a compact LED controller/
driver that interfaces microprocessors to LED
displays through serial I
LEDs connected in common anode configuration
and includes keyscanning for an 8 x 2 key matrix
which automatically scans and de-bounces a
matrix of up to 16 switches.
Furthermore, the STLED325 provides standby
power management to the host. It also integrates
a low-power, highly-accurate RTC and a remotecontrol decoder. All functions are programmable
using the I
2
C bus. Low power consumption during
standby mode is achieved.
The STLED325 controller/driver is ideal as a
single peripheral device to interface the front
panel display with a single-chip host IC like CPU.
2
C interface. It drives
Table 1. Device summary
Order code Temp range (°C) Package Comments
STLED325QTR -40 to +85 °C QFN32 250 parts per reel
April 2011 Doc ID 17576 Rev 1 1/62
www.st.com
62
Contents STLED325
Contents
1 Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2 Functional and application diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3 Functional description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.1 Low power mode of operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.2 I2C serial interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.3 Initial power up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.4 Display types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.5 Keyscan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.6 Timers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.6.1 Guard timer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.6.2 Watchdog timer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
3.7 Power-on-reset and soft-start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
3.8 LED drivers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
3.9 Over temperature cut-off . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
3.10 Standby mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
3.10.1 Cold boot up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
3.10.2 Entering standby mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
3.10.3 Wake-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.11 Real time clock (RTC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.11.1 Reading the real time clock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.11.2 Writing to the real time clock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3.11.3 Register table for RTC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3.11.4 Setting alarm clock registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.11.5 Century bits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
3.11.6 Initial power-on defaults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
3.11.7 Programmable display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
3.11.8 Lookup table with ppm against the calibration register values . . . . . . . . 24
3.12 Remote control decoder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
3.13 Interrupt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
3.14 Ready . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
3.15 Mute . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
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STLED325 Contents
3.16 GPIO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
3.17 Power sense circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
3.17.1 Switchover . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
3.17.2 Battery low warning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
3.17.3 Different power operation modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
3.18 Bus characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
4 Electrical ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
4.1 Absolute maximum ratings (TA = 25 °C, GND = 0 V) . . . . . . . . . . . . . . . . 33
4.2 Recommended operating conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
4.2.1 DC electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
4.3 Power consumption estimation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
4.4 Oscillator and crystal characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
4.5 ESD performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
5 Display RAM address and display mode . . . . . . . . . . . . . . . . . . . . . . . 41
6 KEY matrix and key-input data storage RAM . . . . . . . . . . . . . . . . . . . . 42
7 Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
7.1 Configuration mode setting command . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
7.2 Data setting command . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
7.3 Configuration data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
7.3.1 Interrupt flags . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
7.4 Address setting command . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
7.5 Display control and hotkey setting command . . . . . . . . . . . . . . . . . . . . . . 51
7.6 Keyscanning and display timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
8 State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
8.1 Default state upon power-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
8.2 Initial state . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
9 Remote control protocols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
10 Application information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
10.1 Power supply sequencing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
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Contents STLED325
10.2 ISET variation with RSET . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
10.3 Application diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
11 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
12 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
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STLED325 List of tables
List of tables
Table 1. Device summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Table 2. Register table for RTC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Table 3. Alarm repeat modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Table 4. Century bits examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Table 5. Initial power-on defaults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Table 6. RTC display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Table 7. LUT with ppm against the calibration register values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Table 8. Different power operation modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Table 9. Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Table 10. Absolute maximum ratings (TA = 25 °C, GND = 0 V) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Table 11. Thermal data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Table 12. DC electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Table 13. Voltage drop estimation with RGB LED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Table 14. Capacitance (TA = 25°C, f = 1 MHz) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Table 15. Power supply characteristics (TA = -40 to 85°C) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Table 16. Dynamic switching characteristics (TA = -40 to +85 °C, VCC = 5.0V ± 10%, GND=0.0V, Typ-
ical values are at 25°C). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Table 17. Timing characteristics (TA = -40 to +85 °C, VCC = 5.0 V ± 10%, GND=0.0 V, typical values
are at 25 °C) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Table 18. Oscillator characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Table 19. Crystal electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Table 20. ESD performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Table 21. Battery range and battery detect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Table 22. Power down/up AC characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Table 23. Power down/up trip points DC characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Table 24. Thermal shutdown characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
Table 25. Bit map for segment 1 to segment 8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Table 26. Data write command. b5 b4: 00 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
Table 27. Data Write 2 command. B5 b4: 01 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
Table 28. Data Read 1 command. b5 b4: 10 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
Table 29. Data Read 2 command. b5 b4: 11 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
Table 30. Power-up defaults. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
Table 31. QFN32 (5 x 5 mm) mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
Table 32. Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
Doc ID 17576 Rev 1 5/62
List of figures STLED325
List of figures
Figure 1. Functional block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Figure 2. Application diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Figure 3. Pin configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Figure 4. Display types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Figure 5. Power-up condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Figure 6. Power down condition (normal behavior) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Figure 7. Standby condition (normal behavior) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Figure 8. Keyscan and digit mapping. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Figure 9. Interrupt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Figure 10. Power sense circuit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Figure 11. Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Figure 12. Battery switchover waveform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Figure 13. Power down/up mode ac waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Figure 14. VCC characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
Figure 15. KEY matrix and key-input data storage RAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Figure 16. Data write command (b7 b6) for GPIO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
Figure 17. Interrupt bit mapping in Byte 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
Figure 18. Interrupt bit mapping in Byte 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
Figure 19. Blanking time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
Figure 20. Keyscanning and display timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
Figure 21. Rext versus Iseg curve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
Figure 22. Application schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
Figure 23. QFN32 package dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
Figure 24. QFN32 carrier tape . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
6/62 Doc ID 17576 Rev 1
STLED325 Description
1 Description
The STLED325 is a compact LED controller/driver that interfaces microprocessors to LED
displays through serial I
figuration. The STLED325 drives up to 40 discrete LEDs in 8 segment/5 digit configuration
while functioning from a supply voltage of 5 V. The maximum segment current for the display
digits is set through a single external resistor. Individual digits may be addressed and
updated without rewriting the entire display. Additionally it includes keyscanning for an 8 x 2
key matrix which automatically scans and de-bounces a matrix of up to 16 switches.
Furthermore, it provides standby power management to the host. The STLED325 also
integrates a low-power, highly-accurate RTC and a remote-control decoder. All functions are
pro-grammable using the I
achieved. STLED325 supports numeric-type displays and reduces the overall BOM costs
through high integration. Also it provides ESD protection of greater than 2 kV HBM.
The LED controller/driver is ideal as a single peripheral device to interface the front panel
display with a single-chip Host IC like CPU.
2
C interface. It drives LED connected in common anode con-
2
C bus. Low power consumption during standby mode is
Doc ID 17576 Rev 1 7/62
Functional and application diagram STLED325
2 Functional and application diagram
Figure 1. Functional block diagram
Thermal
Vbat
8
5
Remote Ctrl
protection
Decoder &
Guard
timer
drivers
Segment
Grid
Digit
drivers
Drivers
STDBY
IRQ_N
SEG1/KS1
SEG8/KS8
DIG5
DIG4
DIG1
GND
(0V)
ISET
Vcc
SCL
SDA
WAKE_UP
GPIO1
GPIO2
VREG
MUTE
KEY1-KEY2
Current
source
regulator
XOUT
Voltage
2
2
XIN
SPI
I2C
Seria
Serial
l I/F
I/F
OSC
OSC
(Fixed
Freq)
Output
segments
Internal
core
supply
RTC +
32KHz
Osc
VBAT
Command
Command
Decoder
Decoder
Display Mem
Display Mem
(20 x 16)
(5 x 8)
Timing Gen
Timing Gen
Key Scan &
Key Scan &
Dimming
Dimming
KeyData Mem
KeyData Mem
(2 x 12)
(2 x 8)
IR_IN
and UVLO
RC
decoder
POR &
Soft-start
Bandgap
8-bit
20- bit
output
Output
latch
Latch
16- bit
5-bit
Shift
Shift
Register
Register
READY
Internal
reset
VCC
Detect
Detect
Powe r
management
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AM04143V1
STLED325 Functional and application diagram
Figure 2. Application diagram
Microcontroller or
CPU
External
32.768KHz crystal
From remote
control sensor
R
SCL
SDA
READY
STBY
IRQ_N
MUTE
WAKE_UP
VBAT
STLED325
XIN
XOUT
IR_IN
ISET
KEY1-KEY2
Key scan
(8x2 matrix)
DIG1-DIG4
SEG1/KS1-
SEG8/KS8
DIG5
GPIO1
GPIO2
VREG
2
LED 4-digit 7-segment (+dot-point) display panel
4
8
PWR STBY REC MUTE
From sensor/To LED
From sensor/To LED
Connect to external
capacitor
!-6
Doc ID 17576 Rev 1 9/62
Functional and application diagram STLED325
Figure 3. Pin configurations
MUTE
IRQ_N
GPIO1
GPIO2
IR_IN
SDA
SCL
WAKE_UP
XOUT
30
STLED325
11
DIG3
XIN
29
12
DIG2
GND
28
13
DIG1
VREG
27
14
VCC
VBAT
26
15
KEY2
ISET
25
16
KEY1
24
23
22
21
20
19
18
17
SEG1/KS1
SEG2/KS2
SEG3/KS3
SEG4/KS4
SEG5/KS5
SEG6/KS6
SEG7/KS7
SEG8/KS8
STBY
READY
31
32
1
2
3
4
5
6
7
8
9
10
DIG4
DIG5
!-6
10/62 Doc ID 17576 Rev 1
STLED325 Functional description
3 Functional description
The STLED325 is a common anode LED driver controller which can be used to drive red,
green or blue LEDs as the current is adjustable through the external resistor. In the common
anode configuration, the digit outputs source the current to the anodes while the segment
outputs sink the current from the cathodes. The configurable output current can be used to
drive LEDs with different current ratings (red, green or blue). The brightness can be
controlled through the I
together in parallel to drive a single LED. In this case, two parallel current sources of equal
value drive a single LED. The external resistor value can be set accordingly to determine the
desired output current.
Soft-start limits the inrush current during power-up. The built-in thermal protection turns off
the display when the temperature exceeds 140°C with a small hysteresis of 15°C. The
display is blanked (LEDs are turned off or in high-Z state) on power-up.
3.1 Low power mode of operation
When not used, the STLED325 goes into low power mode of operation wherein the current
consumption drops to less than 1 mA. During this mode, the data configured is maintained
as long as the supply voltage is still present (the contents of the internal RAM need the
supply voltage to be present). Port configuration and output levels are restored when the
STLED325 is taken out of shutdown. For minimum supply current in shutdown mode, logic
inputs should be at GND or V
2
C interface as described later. The outputs can be connected
.
CC
3.2 I2C serial interface
The interface is used to write configuration and display data to the STLED325. The serial
interface comprises of a shift register into which SDA is clocked on the rising edge of the
SCL after a valid start of communication. When communication is stopped, transitions on
SCL do not clock in the data. During this time, the data are parallel-loaded into a latch. The
8-bit data is then decoded to determine and execute the command.
For an overflow condition, if more bytes are written, then they are ignored whereas if more
bytes are read, then the extra bytes are stuffed with 1’s.
3.3 Initial power up
On initial power-up, all control registers are reset, the display is blanked and the STLED325
is in the low-power mode. All the outputs are in high-impedance state at initial power-up.
The SDA is pulled high by an external pull-up resistor. The display driver has to be
configured before the display can be used.
Doc ID 17576 Rev 1 11/62
Functional description STLED325
3.4 Display types
Figure 4. Display types
Seven segment display with dot point and common-anode LED panel
3.5 Keyscan
The full keyscan is illustrated in the later section of the datasheet. One diode is required per
key switch. The keyscan circuit detects any combination of keys being pressed during each
de-bounce cycle.
The keyscan matrix on the STLED325 passes command from the front panel to the host
processor through the SDA pin on STLED325. The STLED325 can be programmed to
wake-up the system from standby using any of the 16 keys pressed on the front panel.
These wake-up keys are also referred to as hot-keys.
3.6 Timers
3.6.1 Guard timer
For safety related applications, a guard timer is integrated in the STLED325. The guard
timer gives enhanced reliability to the device.
The guard timer can be used to detect an out of-control microprocessor. The user programs
the guard timer by setting the desired amount of time-out into the Guard timer. This guard
time has an initial de-fault value of 10s upon first power-up and subsequently can be
configured from 1s to 15s during normal operation. If a time period of longer than 15s is
desired, then the watchdog timer from RTC can be used. It can also be disabled after first
power-up. If the processor does not clear the timer within the specified period, the
STLED325 puts the system in the standby mode.
This is only active from L to H transition on READY or WAKE_UP pin but it is not level-
based. The guard timer count is cleared by the guard timer clear/reset bit. While in normal
mode, the count starts from the previously count value that was in the register. During the
cold boot up or warm boot up, the count starts from the configured value.
12/62 Doc ID 17576 Rev 1
STLED325 Functional description
3.6.2 Watchdog timer
Another watchdog timer is present in the Watchdog timer register at address 09h of the RTC
register map. This watchdog timer can be used to program timer values of greater than 15s.
Bits BMB4-BMB0 store a binary multiplier and the three bits RB2-RB0 select the resolution
where:
000 = 1/16 second (16 Hz);
001 = 1/4 second (4 Hz);
010 = 1 second (1 Hz);
011 = 4 seconds (1/4 Hz); and
100 = 1 minute (1/60 Hz).
The Watchdog timer is programmed by setting the desired timeout into the Watchdog
register, address 09h. The amount of timeout time is determined to be the multiplication of
the 5-bit multiplier value with the resolution values depicted by the watchdog resolution bits.
The Watchdog timer is disabled when its register is cleared by writing a value of 00h.
Hence the Watchdog function is not enabled upon power on. It is enabled when a non-zero
value is written into its register. The Watchdog timer is reset by performing a write to the
watchdog register, then the time-out period starts over.
If the processor does not reset the timer within the specified timeout period, and when the
timeout occurs, the watchdog flag is set. The watchdog timer of RTC is cleared by writing a
00 value and starts again whenever any new value is written to it.
The WatchDogEn Flag can be disabled or enabled by writing to the register bit and the reset
of watchdog timer is done by writing to the register.
3.7 Power-on-reset and soft-start
The device integrates two internal power-on-reset circuits which initialize the digital logic
upon power up. One circuit is for the V
soft-start circuit limits the inrush current and high peak current during power-up. This is done
by delaying the input circuit’s response to the external applied voltage. During soft-start, the
input resistance is higher which lowers the in-rush current when the supply voltage is
applied.
power and the other is for the V
CC
power. The
BAT
Doc ID 17576 Rev 1 13/62
Functional description STLED325
3.8 LED drivers
The constant current capability is up to 40 mA per output segment and is set for all the
outputs using a single external resistor. When acting as digit drivers, the outputs source
current to the display anodes. When acting as segment drivers, the LED outputs sink current
from the display common cathodes. The outputs are high impedance when not being used
as digit or segment drivers.
Each port configured as a LED segment driver behaves as a digitally-controlled constant
current sink. The LED drivers are suitable for both discrete LEDs and common anode (CA)
numeric LED digits. When fully configured as a LED driver, the STLED325 controls up to 8
LED segments in a single digit with individual 8-step adjustment of the constant current
through each LED segment. A single resistor sets the maximum segment current for all the
segments, with a maximum of 40 mA per segment. The STLED325 drives any combination
of discrete LEDs and common anode (CA) digits for numeric displays.
The recommended value of RSET is the minimum allowed value, since it sets the display
driver to the maximum allowed segment current. RSET can be a higher value to set the
segment current to a lower maximum value where desired. The user must also ensure that
the maximum current specifications of the LEDs connected to the drivers are not exceeded.
3.9 Over temperature cut-off
The STLED325 contains an internal temperature sensor that turns off all outputs when the
die temperature exceeds 140°C. The outputs are enabled again when the die temperature
drops below 125°C. Register contents are not affected, so when a driver is over-dissipating,
the external symptom will be the load LEDs cycling between on and off as the driver
repeatedly overheats and cools, alternately turning the LEDs off and then back on again.
This feature will protect the device from damage due to excessive power dissipation. It is
important to have good thermal conduction with a proper lay-out to reduce thermal
resistance.
3.10 Standby mode
By utilizing the standby function, the host processor and other ICs can be turned off to
reduce power consumption. The STLED325 is able to wake-up the system when
programmed hotkeys are detected to signal that the full operation of the system is required.
The hotkeys can be entered to the system through the front panel keys or through the
infrared (IR) remote control or the Real Time Clock (RTC) alarm or through the wake-up pin.
STLED325 supports multiple remote control protocols decoding by setting the appropriate
register.
The STLED325 is able to cut-off the power to the main board for standby operation for good
power management. STBY will be set to high when READY signal goes from high to low, I
command for standby is seen or when the guard timer has finished counting down to 0,
whichever occurs first.
In the normal mode of operation, the STBY is asserted only when the guard timer has
finished counting down to 0. This is meant to put the system into stand-by even though
standby command was not issued by the host or READY signal did not go low. This occurs
as the guard timer register was not cleared before it finished counting down to 0.
2
C
14/62 Doc ID 17576 Rev 1
STLED325 Functional description
3.10.1 Cold boot up
When power is first applied to the system, the STLED325 is reset. It will then manage the
power to the main board by bringing the STBY pin to a low level.
This wakes up the main processor which asserts the READY pin to a high level to indicate to
STLED325 of a proper boot-up sequence.
If the microprocessor does not assert the READY pin to a high within 10s (default), the
STLED325 cuts off the power to the Host by asserting the STBY pin. The high level on
READY pin signifies that the processor is ready. After this, the processor can configure the
STLED325 by sending the various I
RTC display mapping, hot-keys.
The power-up behavior in 2 conditions is shown in Figure 5.
2
C commands for configuration of display, RC protocol,
Doc ID 17576 Rev 1 15/62
Functional description STLED325
Figure 5. Power-up condition
1a) Power-up condition (normal behavior )
VCC to STLED325I
Internal POR
1b) Power-up condition (processor not responding)
VCC to STLED325I
Internal POR
STBY
READY
MUTE
Guard timer counts up to 10s
STBY
READY
MUTE
READY asserts within 10s which is the desired
behavior, processor is active and not hung
Count over
Guard timer counts up to 10s
READY continues to remain low/high
Due to abnormality in the processor, READY did not
change state from low to high, leading to STBY
assertion
Note: 1 Guard timer is turned off by default upon READY assertion.
2 If Guard timer is to be kept on during READY high condition, the guard timer registers must
be set accordingly by proper commands through I
2
C bus.
3 In this power-up condition, Guard timer is triggered by internal POR pulse.
4 During power-up, the Guard timer value is 10s.
16/62 Doc ID 17576 Rev 1
!-6
STLED325 Functional description
3.10.2 Entering standby mode
The STLED325 controls the power to the main board using the STBY pin. During normal
operation, the STBY pin is a low level which externally controls a Power MOS switch to
enable power to the main board. The STLED325 asserts the STBY pin to a high when any
one of the following conditions occur:
– Processor fails to respond by enabling the READY pin within 10s upon first power-up
(cold boot up)
– Guard timer counts down to 0s
– Processor makes the READY pin to low (can happen in various conditions such as
user presses STBY key on front panel, STBY key on remote control, etc).
Figure 6. Power down condition (normal behavior)
2a) Power-down condition (normal behavior )
READY
MUTE
STBY
2 us
Guard timer is not required here
2b) Power-down condition (abnormal behavior of processor)
READY
MUTE
STBY
In this case the READY remains high and as long as
READY is high, the MUTE is low and STBY is low.
READY continues to remain high
!-6
– Guard timer can be kept on during normal condition when READY is high (depending
on the user).
– In this condition, the guard timer can be disabled or enabled. If the guard timer is
enabled, the timer needs to be cleared before the programmed count of the timer is
reached. If the programmed count is reached, the STBY will be asserted.
– It is advisable not to enable the guard timer during normal operation.
Doc ID 17576 Rev 1 17/62
Functional description STLED325
3.10.3 Wake-up
The STLED325 can wake-up from any one of the following sources:
– Front-panel keys
– Remote-control keys
– Real time clock (RTC) in 3 conditions (alarm, watchdog timer, oscillator fail)
– External wake-up pin (by a low to high transition on this pin)
– GPIO status changes
– READY pin goes from low to high
Figure 7. Standby condition (normal behavior)
3a) Standby condition (normal behavior)
or Key pad or RTC or WAKE_UP for wake up
Hot key command from IR
Guard timer triggers
STBY
READY
MUTE
3b) Standby condition (abnormal behavior, processor is not responding)
Hot key command from IR
or Key pad or RTC or WAKE_UP for wake up
STBY
READY
MUTE
READY asserts within programmed timer value (1s-15s)
Guard timer
triggers
Signals STBY after
guard timer count is over
READY continues to remain low
!-6
– When the hot-key is detected either from front-panel or remote control or RTC or from
a transition (low to high transition) on WAKE_UP pin during stand-by, the STBY pin
de-asserts.
– The de-assertion of the STBY triggers the guard timer.
– The timer value is the programmed value by the user (1-15s). If the user did not
change the value before entering standby, then it remains 10s.
– Also note that the guard timer is off when the STLED325 is in the standby mode.
The guard timer is thus triggered by a de-assertion of the STBY signal or by internal power
on reset signal.
18/62 Doc ID 17576 Rev 1
STLED325 Functional description
3.11 Real time clock (RTC)
The STLED325 integrates a low power Serial RTC with a built-in 32.768 kHz oscillator
(external crystal controlled). Eight bytes of the SRAM are used for the clock/calendar
function and are configured in binary coded decimal (BCD) format. An additional 12 bytes of
SRAM provide status/ control of alarm and watchdog functions. Addresses and data are
transferred serially via a two line, bi-directional I
incremented automatically after each WRITE or READ data byte. Note that all 4 digits must
be enabled before using the RTC display.
Functions available to the user include a non-volatile, time-of-day clock/calendar, alarm
interrupts and watchdog timer. The eight clock address locations contain the century, year,
month, date, day, hour, minute, second and tenths/hundredths of a second in 24 hour BCD
format. Corrections for 28, 29 (leap year - valid until year 2100), 30 and 31 day months are
made automatically.
The RTC operates as a slave device through the slave address of the STLED325 on the
serial bus. Access is obtained by implementing a start condition followed by the correct
device slave address. The 16 bytes contained in the device can then be accessed
sequentially in the following order:
–1. Reserved
– 2. Seconds register
– 3. Minutes register
– 4. Hours register
– 5. Day register
– 6. Date register
– 7. Century/month register
– 8. Year register
– 9. Calibration register
– 10. Watchdog register
– 11 - 16. Alarm registers
2
C interface. The built-in address register is
The RTC keeps track of the date and time. Once the date and time are set, the clock works
when the STLED325 is in normal operation and standby operation. Wake-up alarm feature
is also included in the RTC module. The accuracy of the RTC is approximately 20 ppm
(±50secs/month). How-ever this much depends on the accuracy of the external crystal
used.
The wake-up alarm is programmed to wake up once the date and time set are met. This
feature is present in normal and standby mode of operation. Only one date and time is
available for setting.
The real time clock (RTC) uses an external 32.768 kHz quartz crystal to maintain an
accurate internal representation of the second, minute, hour, day, date, month, and year.
The RTC has leap-year correction. The clock also corrects for months having fewer than 31
days.
3.11.1 Reading the real time clock
The RTC is read by initiating a Read command and specifying the address corresponding to
the register of the real time clock. The RTC registers can then be read in a sequential read
mode. Alarms occurring during a read are unaffected by the read operation.
Doc ID 17576 Rev 1 19/62
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