HT1635A/B Wearable Sports Bracelet LED Display Application
2 / 19
AN0393E
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
I
2
C
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. V
DD
=2.4V~5.5V, Ta=25°C.
Symbol
Parameter
Test Conditions
Min.
Typ. Max. Unit
V
DD
Conditions
V
DD
Operating Voltage
–
–
2.4
5.0
5.5
V
I
OL2
ROW Sink Current
5V
V
OL
=0.5V
10
13
–
mA
I
OH2
ROW Source Current
5V
V
OH
=4.5V
-50
-70
–
mA
I
OL3
COM Sink Current
5V
V
OL
=0.5V
250
400
–
mA
I
OH3
COM Source Current
5V
V
OH
=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.
