Holtek HT1635A, HT1635B Application
HT1635A/B Wearable Sports Bracelet LED Display Application
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HT1635A/B Wearable Sports Bracelet
LED Display Application
D/N: AN0393E
Introduction
The HT1635A and HT1635B are Holtek display data memory mapping LED driver
devices, whose driving capacity is up to 352 patterns composed of 44 rows and 8
commons. The HT1635A provides a 4-wire serial interface and the HT1635B provides an
I
2
C interface. Both interfaces are used for MCU data communication. Using the HT66F50
as the host MCU, a demo with two HT1635A devices or two HT1535B devices is taken as
an example in this application note to introduce how to use the HT1635A and HT1635B.
Each HT1635A or HT1635B device on the demo drives 8 commons and 42 rows of RGB
LEDs (8×14 RGB LEDs), showing the wearable sports bracelet LED panel display
functions.
Operating Principles
HT1635A and HT1635B Main Features
• Operating voltage: 2.4V ~ 5.5V
• Integrated 256kHz RC oscillator
• Frame Rate: 100Hz
• Maximum display capacity: 352 patterns (44 rows and 8 commons)
• Up to 88×4 RAM display data storage
• Supports up to 16-level PWM brightness control
• Four blinking modes: Off, 0.5Hz, 1Hz and 2Hz
• COM driving method selectable: NMOS open-drain or PMOS open-drain
• HT1635A provides a 4-wire serial interface, HT1635B provides an I
2
C serial interface
• Cascade function for extending applications
• Package: 64-pin LQFP
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HT1635A/HT1635B Features Description
Communication Interface
Based on their interface difference, the HT1635 series falls into two versions, the
HT1635A and the HT1635B. The HT1635A includes a 4-wire serial communication
interface which has four pins, WRB (Write Serial Clock), DATA (Serial Data), RDB (Read
Serial Clock) and CSB (Chip Select). The HT1635B is supplied in the same package type
as the HT1635A and is basically pin compatible with the HT1635A, with the exception
that the HT1635B includes an I
2
C communication interface which has four different pin
names corresponding to the HT1635A serial interface pins, SCL (Serial Clock), SDA
(Serial Data), A1 (Device Address Data Input Pin) and A0 (Device Address Data Input
Pin), as shown in the table below.
Part Number Interface Type
Interface Pin
17 18 19 20
HT1635A 4-wire DATA WRB RDB CSB
HT1635B I2C SDA SCL A1 A0
COM and ROW I/O Driving Capacity
The HT1635A/HT1635B devices have a strong current driving capacity for COM and
ROW I/Os, more associated parameters are described below. VDD=2.4V~5.5V, Ta=25°C.
Symbol Parameter
Test Conditions
Min. Typ. Max. Unit
VDD Conditions
VDD Operating Voltage – – 2.4 5.0 5.5 V
I
OL2
ROW Sink Current 5V VOL=0.5V 10 13 – mA
I
OH2
ROW Source Current 5V VOH=4.5V -50 -70 – mA
I
OL3
COM Sink Current 5V VOL=0.5V 250 400 – mA
I
OH3
COM Source Current 5V VOH=4.5V -45 -60 – mA
As shown in the above table, the HT1635A/HT1635B devices support a large COM I/O
sink current with a typical value of 400mA, which coupled with the typical -70mA of ROW
I/O source current makes the devices more suitable for driving common cathode LED
matrixes. The current flowing through the LED is associated with the operating voltage
and the LED forward voltage, V
F
. In some applications, users can use a direct drive
method, which means LED anodes are connected to ROW I/Os and LED cathodes are
connected to COM I/Os without requiring any current limiting resistor.
It should be noted that the HT1635A/HT1635B pins LEDVDD and VDD, LEDVSS and
VSS are internally bonded together respectively, which means that driver power pins,
LEDVDD and LEDVSS, and logic power pins, VDD and VSS, are not separated.
HT1635A/B Wearable Sports Bracelet LED Display Application
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COM Driving Methods
Each HT1635A/HT1635B COM pin has two driving types, NMOS open-drain and PMOS
open-drain. No matter what driving type is selected for the COM pins, the ROW pins only
output the data in the corresponding RAM Display Memory. If the RAM is written with a
“1”, its corresponding ROW pin will output a high level, similarly, a “0” value corresponds
to a low level output. The COM driving setup for the two communication interfaces are
shown below.
Communication
Interface
COM Driving
Method
ID Command Code Default Setup
4-wire
NMOS driving
1 0 0
0010-0XXX-X
0010-0XXX-X
(NMOS driving)
PMOS driving 0010-1XXX-X
I2C
NMOS driving
10001000
XXXXXXX0
00H
(NMOS driving)
PMOS driving XXXXXXX1
Note: “X”: 0 or 1
Operating Modes
The HT1635A/HT1635B devices support three operating modes, Master Mode0, Master
Mode1 and Slave Mode. With regard to Master Mode0 and Master Mode1, the system
clock can be sourced from the integrated 256 kHz RC oscillator or from the external clock
on the OSC pin, as shown in the following table.
Name
Master/Slave
Select
Input Clock
Source
OSC Pin
Status
SYNC Pin
Status
Note
RC Master
Mode0
Master Mode
On Chip RC
Oscillator
Output Hi-Z
Always
Output High
Only Single Chip
Application
RC Master
Mode1
Output Output –
EXT CLK
Master Mode0
Master Mode External OSC
Input
Always
Output High
Only Single Chip
Application
EXT CLK
Master Mode1
Input Output –
Slave Mode Slave Mode External OSC Input Input –
The HT1635A/HT1635B SYNC pin is used for LED driving waveform synchronisation
allowing the cascading of more HT1635 devices to drive a larger screen. Regarding the
HT1635A, which has a 4-wire interface, users can make one device operate in the Master
Mode1 and the remaining devices operate in the Slave Mode. Connect the OSC and
SYNC pins of the Master Mode1 device to the corresponding pins on the Slave Mode
devices. Use the host MCU to control the CSB pin on each HT1635A device to achieve
cascade driving. With respect to the HT1635B, which has an I
2
C interface, the A0 and A1
pins can be configured as pull-high or pull-low to setup the I
2
C slave device address. A
four devices cascade function is available.
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After system power is applied, the HT1635A/HT1635B devices will be initialised by an
internal power-on reset circuit. The status of the internal circuits after initialisation is as
follows.
• System oscillator will be off
• COM0~COM7 outputs are high impedance
• ROW outputs will all be low
• The LED display will be in an off state
• ROW outputs are set to 16/16 PWM duty
• The blinking function will be in an off state
It should be noted that data transfers on the 4-wire/I
2
C bus should be avoided for more
than 1ms following a power-on reset to the devices to allow the reset initialisation
operation to complete.
Dimming Circuit
The HT1635A/HT1635B devices have an integrated 16-level PWM dimming circuit. The
dimming circuit uses the command received by the interface to set up the related
dimming register. In this way, all of the ROW outputs duty can be adjusted to implement
the brightness control of the entire display screen. The ROW dimming timing is shown in
the following figure.
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Demo H/W Block Diagram
System Block Diagram
Bottom Board
Top Board
RGB LED Matrix
(8COM x 42ROW x 2
)
HT
1635A
/B
x 2
(64LQFP)
COM/ROW
4-wire/I2C
Power Supply Circuit
AC100
V
~240
V
DC
5V
18650 Li+
Battery
DC
-DC Boost Circuit
(
SY7066)
Micro USB
AC
-
DC Converter
(
FAS
10-
5-
W
)
HT66
F
50
(28SOP)
Li+ Battery
Charger
(APL3202)
Key
x 1
Figure 1 System Block Diagram
The demo PCB is composed of two boards, a top board and a bottom board. The top
board is an RGB LED Matrix board and the bottom board is a power control board. These
two boards are connected using a pin header.
• RGB LED Matrix
Two HT1635A devices or two HT1635B devices jointly drive an RGB LED Matrix
composed of 8 commons and 28 rows.
• Power Supply Circuit
The power supply circuit provides three power supply methods, AC power (100~240VAC),
power adapter (DC5V, Micro USB interface) and a Li-battery (one 18650).
• DC-DC Boost Circuit
When only using the Li-battery to supply power, enable the DC-DC boost IC (SY7066)
which will increase the battery voltage to 5V to supply power for the host MCU and the
HT1635A/HT1635B.
• Li-Battery Charging Circuit
When using the AC power or the external power adapter to supply power, enable the
Li-battery charging management IC (APL3202) to charge the battery.
• Key Section
A touch key is used for switching the display screens.
• Host MCU Section
This demo uses the HT66F50 as the master control MCU to implement data
communication with the HT1635A/HT1635B and achieve various display functions.
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Application Circuits
Figure 2 RGB LED Matrix Circuit
The RGB LED Matrix PCB is available for the HT1635A and HT1635B. Switching
between these two devices can be achieved by using several 0Ω resistors, therefore a
general device name HT1635 is used in the schematic diagram.
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