ST2226A
Version
Issue Date
File Name
Total Pages
: A.010
: 2004/04/12
: SP-ST2226A-A.010.doc
: 23
PWM-Controlled Constant Current Driver for LED
Displays
新竹市科學園區展業一路 9 號 7 樓之 1
SILICON TOUCH TECHNOLOGY INC.
9-7F-1, Prosperity Road I, Science Based Industrial Pard,
Hsin-Chu, Taiwan 300, R.O.C
Fax：886-3-5645626
Tel：886-3-5645656
點晶科技股份有限公司
ST2226A
SILICON TOUCH TECHNOLOGY INC.
ST2226A
PWM-Controlled Constant Current Driver
for LED Displays
General Description
The ST2226A is a LED driver incorporating shift registers, data latches, 16-channel
constant current circuitry with current value set by an external resistor, 1024 gray level
PWM (Pulse Width Modulation) functional unit and time division capability. Each channel
can provide a maximum current of 60 mA. Time division operation allows driving up to 1
or 2 LEDs with a single output channel (mode-1 and mode-2 respectively).
Block Diagram
IOUT0
Rext
GCLK
CMD[2:0]
……
Voltage
Reference
Driver
(16-Channel)
PWM
Counter
Comparator
(16-Channel)
Operation
Control
IOUT15
Shift Register and Latch
(10 Bit ｘ 16-Channel ｘ 2LED)
DCLK
DIN
Figure 1. Functional block diagram
ST2226A
Version：A.010
Page：1
DOUT
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ST2226A
SILICON TOUCH TECHNOLOGY INC.
Features
˙
˙
˙
˙
˙
˙
Constant current outputs with current value settings by an external resistor
Maximum output current: 60 mA
Time division output allows the driving of 1 or 2 LEDs with a single output
Maximum / minimum output voltage: 10V / 1.25V
10 bits luminance data with PWM current outputs
Serial shift-in architecture for luminance data in time division Mode 1 and Mode 2
Absolute Maximum Ratings
Supply Voltage (AVDD, DVDD)
Input Voltage Range (VIN)
Driver Output Voltage Range (VOUT)
Driver Output Current (IOUT)
Power Dissipation (Ta = 50 ℃or less)
Thermal Resistance (Θja)
Operating temperature range (Top)
Storage temperature range (Tstg)
ST2226A
-0.3 to 6
-0.3 to DVDD+0.3
-0.3 to 10
0 to 60
2.50, SDIP28
1.32, SOP28
2.92, QFN32
40.0, SDIP28
75.9, SOP28
34.2, QFN32
-40 to 85
-55 to 150
Version：A.010
V
V
V
mA
W
℃ /W
℃
℃
Page：2
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ST2226A
SILICON TOUCH TECHNOLOGY INC.
Pin Connection (SDIP28 / SOP28 Top View)
Pin Assignment (SDIP28 / SOP28)
ST2226A
Pin No.
NAME
Pin No.
NAME
1
IOUT2
15
IOUT14
2
IOUT3
16
IOUT15
3
IOUT4
17
GND
4
IOUT5
18
DOUT
5
IOUT6
19
GCLK
6
IOUT7
20
DCLK
7
IGND
21
REXT
8
IGND
22
CMD[2]
9
IOUT8
23
CMD[1]
10
IOUT9
24
CMD[0]
11
IOUT10
25
DIN
12
IOUT11
26
VDD
13
IOUT12
27
IOUT0
14
IOUT13
28
IOUT1
Version：A.010
Page：3
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ST2226A
SILICON TOUCH TECHNOLOGY INC.
Pin Connection (QFN32 Bottom View)
IGND
CMD[2]
CMD[1]
CMD[0]
26
IGND
25
24
REXT
DCLK
GCLK
DOUT
27
28
29
30
31
32
1
DIN
GND
23
2
VDD
IOUT15
22
3
IOUT0
IOUT14
21
4
IOUT1
IOUT13
20
5
IOUT2
IOUT12
19
6
IOUT3
IOUT11
18
7
IOUT4
IOUT10
17
16
8
IOUT5
15
14
13
12
IOUT9
IOUT8
IGND
IGND
IGND
Thermal PAD
11
10
9
IGND
IOUT7
IOUT6
Pin Assignment (QFN32)
Pin No.
NAME
Pin No.
NAME
Pin No.
NAME
1
DIN
12
IGND
23
GND
2
VDD
13
IGND
24
DOUT
3
IOUT0
14
IGND
25
GCLK
4
IOUT1
15
IOUT8
26
DCLK
5
IOUT2
16
IOUT9
27
REXT
6
IOUT3
17
IOUT10
28
IGND
7
IOUT4
18
IOUT11
29
IGND
8
IOUT5
19
IOUT12
30
CMD[2]
9
IOUT6
20
IOUT13
31
CMD[1]
10
IOUT7
21
IOUT14
32
CMD[0]
11
IGND
22
IOUT15
Thermal PAD
IGND
ST2226A
Version：A.010
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ST2226A
SILICON TOUCH TECHNOLOGY INC.
Pin Description
NAME
PIN NO.
CMD[2:0] SDIP/SOP:
22, 23, 24
QFN:
30, 31, 32
DIN
SDIP/SOP:
25
QFN:
1
DOUT
SDIP/SOP:
18
QFN:
24
DCLK
SDIP/SOP:
20
QFN:
26
GCLK
SDIP/SOP:
19
QFN:
25
IOUT0-15 SDIP/SOP:
27, 28, 1, 2
3, 4, 5, 6, 9,
10, 11, 12
13, 14, 15,
16
I/O
DESCRIPTION
I Encoded commands for data transfer, time division operation
and PWM display:
CMD[2:0]
Command
[000]: Mode-1 time division operation / No operation for
display
[001]: Mode-2 time division operation / No operation for
display
[010]: Data transfer enable (Shift-In)
[011]: Data latch strobe (Capture)
[100]: First LED emitting
[101]: Second LED emitting
[110]: LED emitting disable / IOUT disable (Stop)
[111]: Test mode
CMD commands are latched at the rising edges of DCLK.
There is one DCLK latency between Shift-in command
latched and data shift-in.
I Serial input for luminance data (time division mode-1/2)
O Serial output for luminance data (time division mode-1/2).
I Synchronous clock input for command and serial data
transfer. The input data of DIN is synchronous to rising edges
of DCLK, and transferred to DOUT on falling edges of DCLK.
I Clock input for PWM operation.
O LED driver outputs.
QFN:
3, 4, 5, 6, 9,
10, 15, 16,
17, 18, 19,
20, 21, 22
ST2226A
Version：A.010
Page：5
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ST2226A
SILICON TOUCH TECHNOLOGY INC.
REXT
VDD
GND
IGND
SDIP/SOP:
21
QFN:
27
SDIP/SOP:
26
QFN:
2
SDIP/SOP:
17
QFN:
23
SDIP/SOP:
7, 8
QFN:
11, 12, 13,
14, 28, 29,
Thermal pad
ST2226A
O Driver current setting. LED current is set to a current value by
connecting an external resistor between REXT and GND.
- Power supply
- Analog and digital ground
- Two ground-pin for driver outputs.
Version：A.010
Page：6
點晶科技股份有限公司
ST2226A
SILICON TOUCH TECHNOLOGY INC.
Recommended Operating Conditions
DC Characteristics
PARAMETER
Supply voltage, DVDD, AVDD
Driver output voltage when driver on, VOUT
Driver output voltage when driver off1, VOUT
Driver output current, IOUT
High-level input voltage, VIH
Low-level input voltage, VIL
High-level output current, IOH
Low-level output current, IOL
Operating free-air temperature2, Top
MIN
4.75
1.25
0
5
0.8DVDD
0
-20
NOM
5
-
MAX
5.25
5
10
60
DVDD
0.2 DVDD
-1
1
80
UNIT
V
V
V
mA
V
V
mA
mA
℃
AC Characteristics
PARAMETER
DCLK clock frequency, fDCLK
DCLK pulse duration, twh / twl
DCLK rise/fall time tr / tf
GCLK clock frequency, fGCLK
GCLK pulse duration, twh / twl
GCLK rise/fall time tr /tf
Setup time, tsu
Hold time, th / twh
TEST
CONDITIONS
High or low level
High or low level
CMD to DCLK
DIN to DCLK
DCLK to CMD
CMD to DCLK
DIN to DCLK
DCLK to CMD
MIN
NOM
MAX
UNIT
20
15
25
25
25
25
25
25
-
15
40
20
20
MHz
ns
ns
MHz
ns
ns
ns
-
ns
-
-
1. The driver output voltage including any overshoot stress has to be compliant with the maximum voltage (10V).
2. Recommended junction temperature range is from –20 to 150 ℃.
ST2226A
Version：A.010
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ST2226A
SILICON TOUCH TECHNOLOGY INC.
Electrical Characteristics
PARAMETER
TEST
CONDITIONS
High-level digital output voltage,
VOH
Low-level digital output voltage,
VOL
Input current, II
Supply current (Digital)
DCLK = 10MHz,
GCLK = 10MHz
Supply current (Analog)
REXT = 2K
Voltage reference, VBG
Rext = 2KΩ
Driver output current, IOUT
Rext = 2KΩ,
VOUT = 2.0V
Driver output leakage current, IOL
Driver current skew between
VOUT = 2V, I =
channels, IOL1
40mA
Driver current skew between
VOUT = 2V, I =
chips, IOL2
40mA
MIN
NOM
MAX
UNIT
DVDD0.5
-
-
-
V
-
0.5
V
-
0.5
±1
µA
mA
1.24
14
1.26
32.2
1.28
mA
V
mA
-
±3
1
±6
µA
%
-
±6
±12
%
Switching Characteristics, CL = 15pF, IOUT = 20mA
PARAMETER
Rise time, tr
Fall time, tf
Propagation delay, td
ST2226A
TEST CONDITIONS
DOUT
IOUT
DOUT
IOUT
GCLK to IOUT
MIN
-
Version：A.010
NOM
5
25
5
25
30
MAX
10
40
10
40
40
Page：8
UNIT
ns
ns
ns
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ST2226A
SILICON TOUCH TECHNOLOGY INC.
Typical Control Method
1) Command Sequence
To manipulate ST2226A, we should properly control the CMD, DIN, DCLK, and GCLK
as following steps:
1. Issue command “Shift-in”, and then enter luminance data DIN. Note that ST2226A
2.
starts to shift-in data at the DCLK rising edge next to the edge which latched
Shift-in command.
After data are completely entered, send command “Capture” to save data in
3.
registers.
Send command “Disable”. This step is needed before the “Emitting” command to
4.
keep the chip synchronized.
Issue command “Emitting” or ”Disable”. Note that:
A.
ST2226A generates its output in one-shot fashion, i.e. the output after (1024)
x TGCLK is always zero.
There are 2 GCLK latencies between the latched LED Emitting/Disable
B.
5.
command and PWM start/stop. This is shown in Figure 2.
Repeat step 1~4. In the same frame, the luminance data doesn’t have to change,
just repeat step 3~4. Note that the second command “Emitting” will be omitted if
(1024) x TGCLK PWM has not finished, unless the “Disable” command is sent in
advance.
The process discussed above could be summarized in the following table and timing
diagram. At the same time, DCLK and GCLK remain free running.
Table 1. Example of Command Sequence
3
Disable
Emitting / Disable
Shift-In
…
Shift-In
Disable
Emitting / Disable
Shift-In
…
Shift-In
Disable
Emitting / Disable
NOP
…
NOP
Capture
…
Don’t care.
Don’t care.
Don’t care.
Shift-in Data.
…
Shift-in Data
Don’t care.
Don’t care.
Shift-in Data
…
Shift-in Data
Don’t care.
Don’t care.
Don’t care.
Don’t care.
…
…
We used the NOPs (No operation) to wait for the next frame data (at 60Hz) ready.
ST2226A
Version：A.010
Page：9
…
Capture
3
Don’t care.
Frame
N+1
NOP
Frame
N
…
…
…
DIN
CMD
Frame
N-1
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ST2226A
SILICON TOUCH TECHNOLOGY INC.
2) LED Emitting Time and Current
ST2226A adjusts the LED luminance using PWM (pulse width modulation) technique.
The luminance data (DV) has a resolution of 10 bits (1024steps) and can be set
independently for each LED. The relationship between Iout, luminance data, and emitting
time is shown in Figure 2.
Current
DV x TGCLK
Iout
2 x GCLK
1024 x TGCLK
Time
“LED Emitting” command issued
Figure 2. PWM Current Output
3) Phase Relationship of DCLK and GCLK
Matching ST2226A’s GCLK and DCLK is an important step in the system design. If
there is a certain length of delay between the rising edge of DCLK and of GCLK, the
command “LED Emitting“& “LED Disable” will not be correctly recognized, which will then
cause the display data loss. It is safe to keep both of GCLK and DCLK rising at the same
time, so that the frequencies of DCLK and GCLK have an integer multiple relationship.
For the design which has a fixed, corresponding clock phase relationship between
GCLK & DCLK, e.g. the display controller is built by FPGAs, this clock phase problem is
unlikely to happen. However, if it dose happen, try to control the clock phase, e.g. invert
GCLK, to solve this problem. On the contrary, for the design which can not control the
clock phase, e.g. the display controller is built by microprocessors, the following sequential
modification on “Emitting” & “Disable” commands is preferred to be employed in the
design:
1.
2.
Gate GCLK.
Issue “Emitting” or “Disable” command.
3.
Let go of GCLK.
ST2226A
Version：A.010
Page：10
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ST2226A
SILICON TOUCH TECHNOLOGY INC.
Timing Diagrams
Figure 3. Timing Diagram
ST2226A
Version：A.010
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ST2226A
SILICON TOUCH TECHNOLOGY INC.
Application Diagrams
ST2226A
Version：A.010
Page：12
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ST2226A
SILICON TOUCH TECHNOLOGY INC.
Detailed Description
1) Time Division Operation
Since ST2226A can drive 1 LED or 2 LEDs, the user can choose either MODE1
luminance data or MODE2 luminance data. After the luminance data is given, a
command should be issued so that the driver can operate in MODE1 or in MODE2.
Figure 4 shows the route of data shift-in in MODE2. Later we will explain the data
structure of MODE1 and MODE2 in more details.
DOUT
DIN
Ch0 LED1
Ch1 LED1
Ch15 LED1
Ch0 LED2
Ch1 LED2
Ch15 LED2
Figure 4. Block Diagram for Primary Bus.
Figure 5. shows how to switch between 2 LEDs. When “LED1 Emitting” command
is sent, LED1 PWM output will start 2 GCLK later. At the same time, the switch of
LED1 should be turned on. On the other hand, LED2 switch should be turned on when
LED2 PWM output starts. Again, “Disable” command must be sent before
“LED1/LED2 Emitting”. By periodically switching the emitting commands and LED
switches, we could drive 2 LEDs per channel.
System
Turn on
one of the
switches
LED1 Emitting
or
LED2 Emitting
One of Iout
ST2226A
Figure 5. System Configuration for MODE 2 Operation
ST2226A
Version：A.010
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ST2226A
SILICON TOUCH TECHNOLOGY INC.
2) Serial Shift-In Luminance Data
In the MODE1 operation, the data for shift registers and latches is set as
{16(channel) x 10 bit (luminance) x 1(led)} whereas in MODE2 operation, the data is
set as {16(channel) x 10 bit (luminance) x 2(led)} configuration. The driver IC can
remember both 2 sets of luminance data.
The serial shift architecture assumes a FIFO (first-in firs-out) discipline, hence in
the MODE1 operation, the most significant bit (MSB, Bit 9, Channel 15) luminance
data is the first data shifted in, whereas the least significant bit (LSB, Bit 0, Channel 0)
is the last data bit in a data set. The data structure for the MODE1 and MODE2 is
shown in the Figure 6. and Figure 7. respectively.
Din
Channe
l
Bit
Position
for
Lumina
-nce
Data
0
1
2
…
15
0
(LSB)
0
0
0
0
1
1
1
1
1
2
2
2
2
2
3
3
3
3
3
4
4
4
4
4
5
5
5
5
5
6
6
6
6
6
7
7
7
7
7
8
8
8
8
8
9
9
9
9
9
(MSB)
Dout
Figure 6. Luminance Data Structure in MODE 1
ST2226A
Version：A.010
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ST2226A
SILICON TOUCH TECHNOLOGY INC.
Din
Channe
l
LED1
Bit
Position
for
Lumina
-nce
Data
Channe
l
LED2
Bit
Position
for
Lumina
-nce
Data
0
1
2
…
15
0
(LSB)
0
0
0
0
1
1
1
1
1
2
2
2
2
2
3
3
3
3
3
4
4
4
4
4
5
5
5
5
5
6
6
6
6
6
7
7
7
7
7
8
8
8
8
8
9
9
9
9
9
0
1
2
…
15
0
0
0
0
0
1
1
1
1
1
2
2
2
2
2
3
3
3
3
3
4
4
4
4
4
5
5
5
5
5
6
6
6
6
6
7
7
7
7
7
8
8
8
8
8
9
9
9
9
9
(MSB)
Dout
Figure 7. Luminance Data Structure in MODE 2
ST2226A
Version：A.010
Page：15
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ST2226A
SILICON TOUCH TECHNOLOGY INC.
3) Driver Current Output
The drive current is set by an external resistor, Rext, connected between the
REXT pin and GND. Varying the resistor value can adjust the current scale ranging
from 5mA to the maximum 60 mA. Note that the REXT pin voltage is designed to be
independent of supply voltage, temperature, and process variation, and is
approximately 1.26V.
The output current could be calculated roughly by the following equation:
Iout = (1.26 / Rext) x 51
The full-scale current IOUT vs. Rext is shown in Figure 8.
Rext - Iout
70
60
Iout (mA/Bit)
50
40
30
20
10
0
0
2
4
6
8
10
12
14
Rext (Kohm)
Figure 8. Driver current as a function of REXT
ST2226A
Version：A.010
Page：16
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ST2226A
SILICON TOUCH TECHNOLOGY INC.
4) Power Rating
For the relationship between power dissipation and operating temperature,
please refer to the following Figure 9.
4
Pd (total Power Dissipation) - W
3.5
3
2.5
2
1.5
1
0.5
0
0
50
100
150
200
Ta (F ree-A ir Tem perature) - C
S D IP
SOP
QFN
Figure 9. Power Dissipation vs. Operating Temperature
5) Advantages for application
To understand what the advantages over ON-OFF type drivers, we assume that
in MODE 1 operation, the frame rate is 60Hz, DCLK & GCLK both run at 10MHz. We
can shift in (1/60Hz)/(1/10MHz)=167K bits per frame. One channel takes 10 bits, thus
167K/10=16.7K channels (single color pixels). For two dimension display, we take the
square root of 16.7K pixels, which equals 129. The resolution, in this case is 129*129.
We can round the data a little bit, and we can construct a 128*128 image by
connecting 1024 driver ICs. (1,024 EA drivers*16 channels≒16,384 bit).
ST2226A
Version：A.010
Page：17
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ST2226A
SILICON TOUCH TECHNOLOGY INC.
Within a frame, there are 1024*16*10=163K DCLK & GCLK cycles, and we know
that the PWM takes 1024 GCLK cycles and is one-shot. So we can issue up to
163K/1024=160 PWM cycles within a frame. This can be used as an 160-level total
brightness control in addition to the 1024-level pixel-dependent luminance control.
These 160- “LED1 Emitting” shall be issued periodically within a frame. Each time
when issuing the “LED1 Emitting” command, the shift-in process will be pended for a
few cycles; however, we can resume feeding the data right after the “LED1 Emitting”
command is issued.
To make the total brightness at full scale, all 160 “LED1 Emitting” commands
should be issued. To make the total brightness half of the full scale, we can issue
80-“LED1 Emitting” commands in companion with 80-“LED Disable” commands, so
that all the 128*128 LEDs are half of their brightness.
A comparison table for PWM LED driver vs. ON-OFF type is provided for
reference.
Table 2. Comparison between PWM and ON-OFF Free Running
PWM
60
128 x 128
1024
160
Frame rate
No. shift-in pixels
Grayscale for each pixel
Grayscale for overall
panel
Clocks needed per frame 167k
Clock rate
10 MHz
ON-OFF
60
128 x 128
1024
1
16.8Meg
1.0 GHz4
4
Surely out of spec. Can’t realize in this configuration. System designs for ON-OFF type drivers thus need to reduce
frame rate or the no. shift-in pixels or grayscale level for each pixel.
ST2226A
Version：A.010
Page：18
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ST2226A
SILICON TOUCH TECHNOLOGY INC.
Package Outline Dimension
SDIP28
B
e
E
A
A2
E1
Θ
D
L
A1
SEATING PLANE
0.018typ.
0.060typ.
0.100typ.
SYMBOLS
A
A1
A2
D
E1
E
L
e
B
θ
DIMENSION IN
MIN. NOM.
0.015
0.125 0.130
1.385 1.390
0.283 0.288
0.31 BSC
0.115 0.130
0.330 0.350
0
7
Note:
1. JEDEC OUTLINE : N/A
ST2226A
Version：A.010
Page：19
INCH
MAX.
0.210
0.135
1.400
0.293
0.150
0.370
15
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ST2226A
SILICON TOUCH TECHNOLOGY INC.
SOP28
ST2226A
Version：A.010
Page：20
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ST2226A
SILICON TOUCH TECHNOLOGY INC.
QFN32
TOP VIEW
BOTTOM VIEW
0.25 C
D2
D
25
32
25
24
8
17
24
1
17
8
L
E
E2
e
1
32
0.25 C
9
16
16
9
e
b
0.10
M
C AB
A
0.10 C
SEATING PLANE
A3
A1
y C
SYMBOL
A
A1
A3
b
D
D2
E
E2
e
L
y
MIN.
0.70
0
0.18
1.25
1.25
0.30
DIMENSION
(mm)
NOM.
0.75
0.02
0.25 REF
0.23
5.00 BSC
2.70
5.00 BSC
2.70
0.50 BSC
0.40
0.10
MAX.
0.80
0.05
MIN.
27.6
0
0.30
7.09
3.25
49.21
3.25
49.21
0.50
11.81
DIMENSION
(MIL)
NOM.
29.5
0.79
9.84 REF
9.06
196.85 BSC
106.30
196.85 BSC
106.30
19.69 BSC
15.75
3.94
MAX.
31.5
1.97
11.81
127.95
127.95
19.69
Note: 1.DIMENSIONING AND TOLERANCING CONFORM TO ASME Y145.5M-1994.
2. REFER TO JEDEC STD. MO-220 WHHD-2 ISSUE A
ST2226A
Version：A.010
Page：21
點晶科技股份有限公司
ST2226A
SILICON TOUCH TECHNOLOGY INC.
The products listed herein are designed for ordinary electronic applications,
such as electrical appliances, audio-visual equipment, communications devices
and so on. Hence, it is advisable that the devices should not be used in
medical instruments, surgical implants, aerospace machinery, nuclear power
control systems, disaster/crime-prevention equipment and the like. Misusing
those products may directly or indirectly endanger human life, or cause injury
and property loss.
Silicon Touch Technology, Inc. will not take any responsibilities regarding the
misusage of the products mentioned above. Anyone who purchases any
products described herein with the above-mentioned intention or with such
misused applications should accept full responsibility and indemnify. Silicon
Touch Technology, Inc. and its distributors and all their officers and employees
shall defend jointly and severally against any and all claims and litigation and
all damages, cost and expenses associated with such intention and
manipulation.
ST2226A
Version：A.010
Page：22