IREF
IREF
IREF
OLCmax
OLCmax
V
(V)
V
(V)
1
BC
R
(k )
Gain
32
I
(mA)
I
(mA)
8
144
§
·
:
u
u
u ¨
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©
¹
Function-Control Description
20
SLVUBF4A – February 2018 – Revised June 2019
Copyright © 2018–2019, Texas Instruments Incorporated
Function Control
TI Information — Selective Disclosure
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
IREF
(See
). BC data can be set through the serial interface.
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
GAIN
RATIO OF GAIN
/ GAIN_MAX (AT
MAX BC)
I
OUT
(mA) (I
OLCmax
= 25
mA, TYP)
I
OUT
(mA) (I
OLCmax
=
2.4 mA, TYP)
BINARY
DECIMAL
HEX
000 0000
0
00
4
12.5%
3.13
0.3
000 0001
1
01
4.22
13.19%
3.3
0.32
000 0010
2
02
4.44
13.88%
3.47
0.33
...
...
...
...
...
...
...
011 0101
53
35
15.78
49.31%
12.33
1.18
011 0110
(Default)
54 (Default)
36 (Default)
16
50%
12.5
1.2
011 0111
55
37
16.22
50.69%
12.67
1.22
...
...
...
...
...
...
...
111 1101
125
7D
31.78
99.31%
24.83
2.38
111 1110
126
7E
32
100%
25
2.40
111 1111
127
7F
32.22
100.69%
25.17
2.42
2.3.1.2
Select R
IREF
for Maximum Channel Current
The maximum current per channel, I
OLCmax
, is determined by resistor R
IREF
, placed between the IREF and
GND pins. The voltage on IREF is typically 0.8 V. R
IREF
can be calculated by
.
where
•
V
IREF
is the internal reference voltage on IREF (0.8 V, typical)
•
I
OLCmax
is the maximum current for each channel (see
•
Gain is the current gain at each BC (See
)
(1)
R
IREF
must be between 1.02 k
Ω
and 10.7 k
Ω
in order to hold the channel sink current I
OLC
between 25 mA
(typ) and 0.3 mA (typ). Otherwise, the output may be unstable.
Table 2-12. Maximum Constant Current vs External Resistor R
IREF
I
OLCmax
(mA)
R
IREF
(k
Ω
, typ)
25
1.02
20
1.28
15
1.71
10
2.56
5
5.12
2.4
10.7