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Function-Control Description
2.3
Function-Control Description
2.3.1 Global Brightness Control and Current Setting
2.3.1.1
Global Brightness Control (BC)
The TLC694x device is able to adjust the output current of all constant-current outputs simultaneously.
This function is called global brightness control (BC). The global BC for all outputs is programmed with a
7-bit word, thus all output currents can be adjusted in 128 steps from 12.5% to 100.69% for a given
current-programming resistor, R
When the BC data changes, the output current also changes immediately. When the device is powered
on, the default BC data in the function-control register is set to 36h as the initial value.
Table 2-11. Global BC Data vs Constant-Current Ratio and Set Current Value
BC DATA
BINARY
DECIMAL
000 0000
0
000 0001
1
000 0010
2
...
...
011 0101
53
011 0110
54 (Default)
(Default)
011 0111
55
...
...
111 1101
125
111 1110
126
111 1111
127
2.3.1.2
Select R
for Maximum Channel Current
IREF
The maximum current per channel, I
GND pins. The voltage on IREF is typically 0.8 V. R
:
R
(k )
IREF
where
•
V
is the internal reference voltage on IREF (0.8 V, typical)
IREF
•
I
OLCmax
•
Gain is the current gain at each BC (See
R
must be between 1.02 kΩ and 10.7 kΩ in order to hold the channel sink current I
IREF
(typ) and 0.3 mA (typ). Otherwise, the output may be unstable.
I
OLCmax
25
20
15
10
5
2.4
20
Function Control
TI Information — Selective Disclosure
(See
Table
IREF
GAIN
HEX
00
01
4.22
02
4.44
...
35
15.78
36 (Default)
37
16.22
...
7D
31.78
7E
7F
32.22
, is determined by resistor R
OLCmax
V
(V)
IREF
u
Gain
I
(mA)
I
OLCmax
OLCmax
is the maximum current for each channel (see
Table 2-12. Maximum Constant Current vs External Resistor R
(mA)
Copyright © 2018–2019, Texas Instruments Incorporated
2-11). BC data can be set through the serial interface.
RATIO OF GAIN
/ GAIN_MAX (AT
MAX BC)
4
12.5%
13.19%
13.88%
...
...
49.31%
16
50%
50.69%
...
...
99.31%
32
100%
100.69%
can be calculated by
IREF
V
(V)
§
1
BC
IREF
u
u ¨
32
©
(mA)
8 144
Table
2-11)
Table
2-12)
R
IREF
SLVUBF4A – February 2018 – Revised June 2019
I
(mA) (I
= 25
I
(mA) (I
OUT
OLCmax
OUT
mA, TYP)
2.4 mA, TYP)
3.13
3.3
3.47
...
12.33
12.5
12.67
...
24.83
25
25.17
, placed between the IREF and
IREF
Equation
1.
·
¸
¹
between 25 mA
OLC
IREF
(kΩ, typ)
1.02
1.28
1.71
2.56
5.12
10.7
Submit Documentation Feedback
www.ti.com
=
OLCmax
0.3
0.32
0.33
...
1.18
1.2
1.22
...
2.38
2.40
2.42
(1)
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