IS31FL3731-QFLS2-TR ISSI, IS31FL3731-QFLS2-TR Datasheet - Page 16

• Manufacturer Part Number: IS31FL3731-QFLS2-TR
• Description: LED Lighting Drivers LED Driver
• Manufacturer: ISSI

Specifications of IS31FL3731-QFLS2-TR

• Input Voltage: 2.7 V to 5.5 V
• Operating Frequency: 400 kHz
• Maximum Supply Current: 2.17 mA
• Output Current: 34 mA
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Package / Case: QFN-28
• Minimum Operating Temperature: - 40 C
• Factory Pack Quantity: 2500

C(16)
C(24)
IS31FL3731
APPLICATION INFORMATION (The description below is for the Function Register unless otherwise noted.)
PWM CONTROL
The brightness of 144 LEDs can be modulated with
256 steps by PWM Register. For example, if the data
in PWM Register is “0000 0100”, then the PWM is the
fourth step.
Writing new data continuously to the registers can
modulate the brightness of the LEDs to achieve a
breathing effect.
GAMMA CORRECTION
In order to perform a better visual LED breathing effect
we recommend using a gamma corrected PWM value
to set the LED intensity. This results in a reduced
number of steps for the LED intensity setting, but
causes the change in intensity to appear more linear to
the human eye.
Gamma correction, also known as gamma
compression or encoding, is used to encode linear
luminance to match the non-linear characteristics of
display. Since the IS31FL3731 can modulate the
brightness of the LEDs with 256 steps, a gamma
correction function can be applied when computing
each subsequent LED intensity setting such that the
changes in brightness matches the human eye's
brightness curve.
Table 17 32 gamma steps with 256 PWM steps
Choosing more gamma steps provides for a more
continuous looking breathing effect. This is useful for
very long breathing cycles. The recommended
Integrated Silicon Solution, Inc. – www.issi.com
Rev.B, 09/10/2012
C(0)
C(8)
161
22
78
0
C(17)
C(25)
C(1)
C(9)
173
256
224
192
160
128
28
86
1
96
64
32
0
0
Figure 9 Gamma Correction(32 Steps)
C(10)
C(18)
C(26)
C(2)
186
4
33
96
2
8
C(19)
C(27)
C(11)
C(3)
106
199
39
4
12
Intensity Steps
C(12)
C(20)
C(28)
C(4)
116
212
16
46
6
20
C(13)
C(21)
C(29)
C(5)
126
226
10
53
24
C(14)
C(22)
C(30)
C(6)
138
240
28
13
61
32
C(15)
C(23)
C(31)
C(7)
149
255
18
69
C(16)
C(24)
C(32)
C(40)
C(48)
C(56)
C(0)
C(8)
configuration is defined by the breath cycle T. When
T=1s, choose 32 gamma steps, when T=2s, choose
64 gamma steps. The user must decide the final
number of gamma steps not only by the LED itself,
but also based on the visual performance of the
finished product.
Table 18 64 gamma steps with 256 PWM steps
158
209
Note: The data of 32 gamma steps is the standard value and the
data of 64 gamma steps is the recommended value.
OPERATING MODE
IS31FL3731 has three operating modes, Picture
Mode, Auto Frame Play Mode and Audio Frame Play
Mode.
PICTURE MODE
By setting the MODE bit of the Configuration Register
(00h) to “00”, the IS31FL3731 operates in Picture
Mode. Set the PFS bit of Picture Display Register
(01h) to choose the display frame. The Picture Mode
114
24
47
77
0
8
C(17)
C(25)
C(33)
C(41)
C(49)
C(57)
256
224
192
160
128
C(1)
C(9)
164
216
119
96
64
32
10
26
50
81
1
0
0
Figure 10 Gamma Correction(64 Steps)
C(10)
C(18)
C(26)
C(34)
C(42)
C(50)
C(58)
8
C(2)
124
170
223
12
29
53
85
2
16
C(11)
C(19)
C(27)
C(35)
C(43)
C(51)
C(59)
C(3)
129
176
230
14
32
57
89
3
24
Intensity Steps
C(12)
C(20)
C(28)
C(36)
C(44)
C(52)
C(60)
C(4)
134
182
237
32
16
35
61
94
4
40
C(13)
C(21)
C(29)
C(37)
C(45)
C(53)
C(61)
C(5)
140
188
244
18
38
65
99
5
48
C(14)
C(22)
C(30)
C(38)
C(46)
C(54)
C(62)
C(6)
104
146
195
251
56
20
41
69
6
64
C(15)
C(23)
C(31)
C(39)
C(47)
C(55)
C(63)
C(7)
109
152
202
255
22
44
73
7
16