IS31FL3218-QFLS2-TR ISSI, IS31FL3218-QFLS2-TR Datasheet - Page 9

• Manufacturer Part Number: IS31FL3218-QFLS2-TR
• Description: LED Lighting Drivers 18-Ch LED Drvr
• Manufacturer: ISSI

Specifications of IS31FL3218-QFLS2-TR

• Operating Frequency: 400 kHz
• Maximum Supply Current: 5.25 mA
• Output Current: 38 mA
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Package / Case: QFN-24
• Factory Pack Quantity: 2500

IS31FL3218
APPLICATION INFORMATION
PWM CONTROL
The PWM Registers (01h~12h) can modulate LED
brightness of 18 channels with 256 steps. 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.
R
The maximum output current of OUT1~OUT18 can be
adjusted by the external resistor, R
Formula (2).
x = 58.5, V
The recommended minimum value of R
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 IS31FL3218 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 7 32 gamma steps with 256 PWM steps
C(16)
C(24)
Integrated Silicon Solution, Inc. – www.issi.com
Rev.B, 03/28/2012
C(0)
C(8)
161
22
78
EXT
0
C(17)
C(25)
C(1)
C(9)
173
28
86
1
OUT
C(10)
C(18)
C(26)
= 0.8V, V
I
C(2)
186
33
96
MAX
2

C(11)
C(19)
C(27)
C(3)
106
199
x
39
4
EXT

V
R
EXT
= 1.3V.
EXT
C(12)
C(20)
C(28)
C(4)
116
212
46
6
EXT
C(13)
C(21)
C(29)
C(5)
126
226
10
53
, as described in
(2)
EXT
C(14)
C(22)
C(30)
is 2kΩ.
C(6)
138
240
13
61
C(15)
C(23)
C(31)
C(7)
149
255
18
69
C(16)
C(24)
C(32)
C(40)
C(48)
C(56)
Choosing more gamma steps provides for a more
continuous looking breathing effect. This is useful for
very long breathing cycles. The recommended
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 8 64 gamma steps with 256 PWM steps
C(0)
C(8)
158
209
114
24
47
77
0
8
C(17)
C(25)
C(33)
C(41)
C(49)
C(57)
C(1)
C(9)
256
224
192
160
128
119
164
216
10
26
50
81
96
64
32
1
0
0
Figure 6 Gamma Correction(32 Steps)
C(10)
C(18)
C(26)
C(34)
C(42)
C(50)
C(58)
C(2)
4
124
170
223
12
29
53
85
2
8
C(11)
C(19)
C(27)
C(35)
C(43)
C(51)
C(59)
C(3)
129
176
230
14
32
57
89
3
12
Intensity Steps
C(12)
C(20)
C(28)
C(36)
C(44)
C(52)
C(60)
C(4)
16
134
182
237
16
35
61
94
4
20
C(13)
C(21)
C(29)
C(37)
C(45)
C(53)
C(61)
C(5)
140
188
244
18
38
65
99
5
24
C(14)
C(22)
C(30)
C(38)
C(46)
C(54)
C(62)
C(6)
104
146
195
251
28
20
41
69
6
32
C(15)
C(23)
C(31)
C(39)
C(47)
C(55)
C(63)
C(7)
109
152
202
255
22
44
73
7
9