Dedicated Circuit for 3-channel LED Constant

Current Drive TM1914A

Overview

TM1914A is a dedicated circuit for single-wire 3-channel LED constant current drive. Its input can be
achieved through the mutual switching of the two-channel digital interfaces (DIN, FDIN) which are cascaded
with DO port. The external controller only needs a single wire to control the chip which integrates with MCU
single-wire two-channel digital interface, data latch, LED constant current drive, PWM luminance control and
other circuits. VDD pin integrates with 5V voltage-regulator tube, with few peripheral devices. The product
applies to guardrail tube, point light source and other LED decoration products. It boasts excellent
performance and reliable quality.

Features

 Low power consumption CMOS workmanship

 OUT output port withstand voltage 24V
 VDD has built-in 5V voltage-regulator tube, supporting 6-24V voltage after connected in series with
resistors
 18mA fixed constant current output
 PWM luminance control circuit, 256-level luminance control
 Accurate current output value
Maximum error (between channels): ±3%
Maximum error (between chips): ±5%
 Single-wire serial cascaded interface
 Single-wire two-channel serial concatenated interface: The chip data interface can configure DIN or
FDIN pin input through the command. In normal mode, the input interfaces switch with each other.
In DIN operating mode, DIN pin inputs data. In FDIN operating mode, FDIN pin inputs data. D0
pins forward cascaded data. The signal does not affect the normal operation of other chips because of
the abnormity of a certain chip.
 Oscillation mode: built-in RC oscillation, clock synchronization according to the signals on the data
line, automatically regenerate the subsequent data after receiving the data of the current unit and
send it to the next level through the data output end, the signals do not distort or attenuate with the
farther distance of cascade connection
 Built-in power-on reset circuit, all registers are zero-initialized after power-on reset
 Data transmission rate 800KHz
 Packaging mode: SOP8

Block diagram for internal structure

DIN
Serial Integer
decoding forwarding DO
FDIN

VDD PWM control

OUTR
VDD Constant
current OUTG
output
GND GND OUTB
OSC

Figure 1

Configuration of SOP8 pins

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 Dedicated Circuit for 3-channel LED Constant
Current Drive TM1914A

OUTR 1 8 VDD
OUTG 2 7 FDIN
Top View
OUTB 3 6 GND
DO 4 5 DIN
Figure 2
Pin function

Pin name Pin number I/O Function description

DIN 5 I Data input
FDIN 7 I Backup data input
DO 4 O Data output
OUTR 1 O N tube open-drain, constant-current output
OUTG 2 O N tube open-drain, constant-current output
OUTB 3 O N tube open-drain, constant-current output
VDD 8 -- Positive pole of power supply
GND 6 -- Power ground

Input/output equivalent circuit

VDD VDD OUT

DIN/FDIN DO

GND GND GND

Figure 3

Integrated circuit is an electrostatic sensitive device which tends to generate a lot of static electricity when used in a
dry season or dry environment. Electrostatic discharge may damage integrated circuit. Titan Micro Electronics
suggests taking all appropriate preventive measures for integrated circuit. Improper operation and welding might
cause ESD damage or performance reduction and chip operation failure.

Limit parameters

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 Dedicated Circuit for 3-channel LED Constant
Current Drive TM1914A

Parameter name Parameter symbol Limit value Unit

Logic supply voltage VDD -0.4～+7.0 V
Voltage of DIN and FDIN ports Vin -0.4～VDD+0.7 V
OUT port voltage Vout -0.4～+32.0 V
Operating temperate range Topr -40～+85 ℃
Storage temperature range Tstg -50～+150 ℃
Human body model (HBM) 3000 V
ESD
Machine model (MM) 300 V
(1) When the chip works for a long time under the above limit parameters, it may cause device reliability reduction or permanent
damage. We do not suggest the chip works by exceeding these limit parameters under any other conditions.
(2) All voltage values are comparatively tested in a systematic way.

Recommended operating conditions

Tested under -45℃-+85℃, unless otherwise specified TM1914A
Parameter Min. Typical Max. Unit
Parameter name Testing condition
symbol value value value
Supply voltage VDD 4.5 5.0 6.5 V
VDD = 5V, DIN and FDIN
Voltage of DIN and
Vin are connected in series with VDD+0.4 V
FDIN ports
a 1KΩ resistor
VDD = 5V, DO are
Voltage of DO ports Vdo connected in series with a VDD+0.4 V
1KΩ resistor
SET port voltage Vset VDD=5V VDD+0.4 V
OUT port voltage Vout OUT＝OFF 24.0 V

Electrical characteristics
Tested under VDD = 3.0-5.5V and operating temperature =
TM1914A
-40℃-+85℃, unless otherwise specified
Parameter Min. Typical Max. Unit
Parameter name Testing condition
symbol value value value
High level output
Voh Ioh=3mA VDD-0.5 V
voltage
Low level output
Vol Iol=10mA 0.4 V
voltage
High level input voltage Vih VDD=5.0V 3.5 VDD V
Low level input voltage Vil VDD=5.0V 0 1.5 V
High level output
Ioh VDD=5.0V, Vdo=4.9V 1 mA
current
Low level output
Iol VDD=5.0V, Vdo=0.4V 10 mA
current
DIN and FDIN connect
Input current Iin 1 μA
with VDD
VDD=4.0V, GND=0V,
Quiescent current IDD 0.5 1.2 1.5 mA
other ports are suspended
OUT output constant OUTR, OUTG,
Iout 17.1 18 18.9 mA
current OUTB=ON, Vout=3.0V
OUT output leakage OUTR, OUTG,
Iolkg 0.5 μA
current OUTB=OFF, Vout=24.0V
Constant-current error OUTR, OUTG,
ΔIolc0 ±3 %
between channels OUTB=ON, Vout=3.0V
Constant-current error OUTR, OUTG,
ΔIolc1 ±5 %
between chips OUTB=ON, Vout=3.0V
Consumed power Pd Ta=25℃ 250 mW

Switch characteristics

Tested under VDD = 3.0-5.5V and operating temperature =

TM1914A Unit
-40℃-+85℃, typical value VDD = 5.0V, TA = +25℃, unless
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 Dedicated Circuit for 3-channel LED Constant
Current Drive TM1914A
otherwise specified
Parameter Min. Typical Max.
Parameter name Testing condition
symbol value value value
Data rate Fin 800 KHz
OUT PWM output
Fout OUTR, OUTG, OUTB 666 Hz
frequency
DIN → DO
Propagation delay time Tplz 155 ns
FDIN → DO
Input capacitance Ci 15 pF

Time sequence characteristics

Parameter Testing Min. Typical Max.

Parameter name Unit
symbol condition value value value
Input 0 ode, low level time T0l 310 360 410 ns
Input 1 ode, low level time T1l 650 720 1000 ns
Output 0 ode, low level time T0l’ VDD=5.0V 350 ns
Output 1 ode, low level time T1l’ GND=0V 700 ns
0 code or 1 code cycle T0/T1 1.25 μs
Reset code, high level time Treset 200 μs
(1) When 0 code or 1 code cycle is within the range of 1.25μs (frequency 800KHz) to 2.5μs (frequency 400KHz), the chip can
normally work, but the low level time of 0 code and 1 code must accord with the corresponding values in the above table;
(2) When reset is not required, the high level time between bytes should not exceed 50μs, or else the chip may be rest to receive
data again, which cannot achieve correct data transmission.

T0 T1 Treset

T0l T1l

Vth
DIN/FDIN

Vtl

Tplz

DO

T0l' T1l' Treset

Figure 4

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 Dedicated Circuit for 3-channel LED Constant
Current Drive TM1914A

Function description

1. Mode setting

The chip adopts single-wire two-channel communication and adopts 1-code mode to send signals. A
correct operating mode should be configured before the chip receivers display data to select the mode of
display data. A mode setting command totally contains 48 bits, in which the former 24 bits belong to the
command code and the latter 24 bits belong to check ones-complement code. After reset, the chip begins to
receive data. There are totally 3 kinds of mode setting commands as follows:
(1) 0xFFFFFF_000000:
The chip is configured as normal operating mode. In this mode, it is defaulted for the first time that DIN
receives display data. When the chip detects that this port has signal input, it will always maintain reception by
this port. In case no data is received for more than 300ms, it will switch to that FDIN receives display data.
When the chip detects that this port has signal input, it will always maintain reception by this port. In case no
data is received for more than 300ms, it will switch to that DIN receives display data again. DIN and FDIN
switch in a circulatory way to receive display data.
(2) 0xFFFFFA_000005 command:
The chip is configured as DIN operating mode. In this mode, the chip only receives the display data input from
DIN port and FDIN port data is invalid.
(3) 0xFFFFF5_00000A command:
The chip is configured as FDIN operating mode. In this mode, the chip only receives the display data input
from FDIN port and DIN port data is invalid.

2. Display data

After power-on reset and reception of a mode setting command, the chip begins to receive display data.
When the 24-bit data are received, DO ports will start to forward the data continuously sent from DIN or FDIN
port, which provides display data for the next cascaded chip. Prior to forwarding data, DO ports are always at
high level. If DIN or FDIN port is input with Reset signals, chip OUT port will output the PWM waveform of
corresponding duty ratio according to the received 24-bit data, and the chip will wait to receive new data again.
Upon receiving the initial 24-bit data, DO port will forward the data. Before the chip receives no Reset signal,
the original output of OUTR, OUTG and OUTB remains unchanged.
The chip adopts auto integer forwarding technology, so that the signals will not distort and attenuate. For
all the cascaded chips, the cycles of data transmission are consistent.

3. Structure of a complete frame of data

C1 and C2 are mode setting commands and each contains 24 data bits. Each chip receives and forwards
C1 and C2, in which 0xFFFFFF_000000 is normal operating mode command, 0xFFFFFA_000005 is DIN
operating mode command, and 0xFFFFF5_00000A is FDIN operating mode command.
The data formats of D1, D2, D3, D4,…Dn are the same, wherein D1 means the display data packet of
the first cascaded chip and Dn means the data display packet of the nth cascaded chip. Each display data packet
contains 24 data bits. Reset means reset signal, valid at high level.

4. Data format of Dn

Each data packet contains 8×3 data bits, with higher bits sent first.

R[7:0]: used to set the PWM duty ratio output by OUTR. Full 0 code is off, full 1 code is of maximum
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 Dedicated Circuit for 3-channel LED Constant
Current Drive TM1914A
duty ratio, 256-level adjustable.
G[7:0]: used to set the PWM duty ratio output by OUTG. Full 0 code is off, full 1 code is of maximum
duty ratio, 256-level adjustable.
B[7:0]: used to set the PWM duty ratio output by OUTB. Full 0 code is off, full 1 code is of maximum
duty ratio, 256-level adjustable.

5. Data reception and forwarding

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 Dedicated Circuit for 3-channel LED Constant
Current Drive TM1914A

Application information

1. Typical application circuit

Figure 7
Annotation: If the controller is only one port signal, the first point of FDIN impending, DIN is connected to the controller,
the other click the above link

To prevent chip signal input/output pin damage caused by the transient peak voltage generated by hot
plugging when the product is tested, 100Ω protective resistors should be connected in parallel at signal input
and output pins. Besides, the 104 decoupling capacitance of each chip in the figure is indispensable, and the
wiring to the VDD and GND pins of the chips should be as short as possible, in order to achieve optimal
decoupling effect and stable chip operation.

2. Power configuration
TM1914A can be configured with DC6-24V power supply, but different power resistors should be
configured according to different input voltages. Calculation method of resistance: when the current of VDD
port is 10mA, VDD series resistance R = (DC-5.5V) ÷ 10mA (DC is supply voltage).
Typical values of configured resistors are as shown in the following table:
Supply voltage (DC) Suggested power interface and VDD series resistance
value
5V No need of connection of resistors, internal voltage-regulator tube
malfunctions
6V 50Ω
9V 350Ω
12V 650Ω
24V 1.8KΩ

3. Functions of different operating modes

In the process of normal use, the chips should be set as normal operating mode. To switch data input
through DIN and FDIN and data output through DO can effectively prevent abnormal transmission of data
caused by the damage of the data input or output port of a chip or the damage of the entire chip.
In the process of aging and installation, the chips can be set as DIN operating mode and FDIN operating
mode to test the chips and their wire connectivity, in a way to discover chip damage, bad wire connection or
other hidden dangers in a timely manner.

4. How to calculate the data refresh rate

The data refresh time is calculated according to how many pixel points are cascaded in one system. A set
of RGB is usually a pixel (or a segment), a TM1914A chip can control a set of RGB.
Calculated according to the normal mode:
1-bit data cycle is 1.25μs (frequency 800KHz), and 1-pixel data contains R (8 bits), G (8 bits) and B (8
bits), totally 24 bits. The transmission time is 1.25μs × 24 = 30μs. If one system contains 1,000 pixel points,
the time for refreshing full display once is 30μs × 1000 = 30ms (omitting C1, C2 and Reset signal time), i.e.,
the refresh rate of one second is: 1 ÷ 30ms ≈ 33Hz.
The following table shows the highest data refresh rates corresponding to cascaded pixel points:
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 Dedicated Circuit for 3-channel LED Constant
Current Drive TM1914A
Normal mode
Fastest time for refreshing Highest data refresh rates
Pixel points
data once (ms) (Hz)
1～400 12 83
1～800 24 41
1～1000 30 33

5. How to make TM1914A work under optimal constant current state

The SET pin connected to GND of TM1914A applies to constant current drive. According to the constant
current curve, when OUT port voltage reaches 0.8V, TM1914A will enter the constant current state. However,
it does not mean it is better when the voltage is higher, because when the voltage is higher, the power
consumption of the chip will be larger and the heating will be more serious, which lowers the reliability of the
whole system. It is suggested that the voltage is 1.2-3V when OUT port is opened. Series resistance can be
adopted to lower the excessive voltage of OUT port. The following is the calculation method for selecting
resistance values:
System drive voltage: DC
Single LED breakover voltage drop: Vled
Series LED number: n
Constant current value: Iout
Constant current voltage: 1.5V
Resistance: R
R= (DC-1.5V-Vled×n) ÷ Iout
For example, system power supply: DC24V, single LED breakover voltage drop: 2V, number of series
LED: 6, constant current value: 18mA, calculated according to the above formula: R= (24V-1.5V-6V×2)÷18
mA≈583Ω. Only need to connect in series about 583Ω resistance at OUT port.

6. How to use TM1914A current expansion

The output constant current of each OUT port of TM1914A is 18mA. If the user needs to expand the
drive current, it can be used after the three OUT ports of RGB are short-circuited. The maximum constant
current value will be increased by 18mA once every OUT port is short-circuited. After all the three OUT ports
are short-circuited, the maximum constant current value can be 54mA. This method should be used along with
software, respectively writing three sets of register values, which can realize accurate current control and
larger drive current.

DC VDD
OUTR LED
OUTG DC
GND
OUTB

Upper level of
cascade connection DIN Lower level of
DO cascade connection
Upper upper level of
cascade connection FDIN

Figure 89

Constant current curve

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 Dedicated Circuit for 3-channel LED Constant
Current Drive TM1914A
When TM1914A is applied in LED product design, the current difference between channels and chips are
very small. When the voltage of the load end changes, the stability of its output current will not be affected.
The constant current curve is as shown in the following figure:

OUT
OUT驱动 U-I曲线
drive U-I curve
20
18
16
14
Current: mA

12 OUTR
10 OUTG
8 OUTB
6
4
2
0
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
OUT port voltage: V

Figure 9

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 Dedicated Circuit for 3-channel LED Constant
Current Drive TM1914A
Packaging diagram (SOP 8)

A2
A
A1
θ
b

C
e L

D E1
E

Dimensions In Millimeters Dimensions In Inches

Symbol
Min Max Min Max
A 1.350 1.750 0.053 0.069
A1 0.100 0.250 0.004 0.010
A2 1.350 1.550 0.053 0.061
b 0.330 0.510 0.013 0.020
c 0.170 0.250 0.006 0.010
D 4.700 5.100 0.185 0.200
E 3.800 4.000 0.150 0.157
E1 5.800 6.200 0.228 0.244
e 1.270(BSC) 0.050(BSC)
L 0.400 1.270 0.016 0.050
θ 0° 8° 0° 8°

(All specs and applications shown above are subject to change without prior notice.)

Version revision history

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 Dedicated Circuit for 3-channel LED Constant
Current Drive TM1914A

Version Date of issue Modification introduction

V1.0 2015-10-21 First version issue

V1.1 2016-04-18 Revised issue

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V1.1