MAX6957 MAXIM [Maxim Integrated Products], MAX6957 Datasheet - Page 13

• Manufacturer Part Number: MAX6957
• Description: 4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and 28-Port LED Display Driver and I/O Expander
• Manufacturer: MAXIM [Maxim Integrated Products]

Table 3. Register Address Map (continued)
Note: Unused bits read as 0.
These registers select the LED’s constant-current drive
from 16 equal fractions of the maximum segment cur-
rent. The current difference between successive cur-
rent steps, I
formula:
If I
Bicolor digits group a red and a green die together for
each display element, so that the element can be lit
red, green (or orange), depending on which die (or
both) is lit. The MAX6957 allows each segment's cur-
rent to be set individually from 1/16th (minimum current
and LED intensity) to 16/16th (maximum current and
LED intensity), as well as off (zero current). Thus, a
bicolor (red-green) segment pair can be set to 289
color/intensity combinations. A discrete or CA tricolor
(red-green-yellow or red-green-blue) segment triad can
be set to 4913 color/intensity combinations.
8 ports 16–23
8 ports 17–24
8 ports 18–25
8 ports 19–26
8 ports 20–27
8 ports 21–28
8 ports 22–29
8 ports 23–30
8 ports 24–31
7 ports 25–31
6 ports 26–31
5 ports 27–31
4 ports 28–31
3 ports 29, 30, 31
2 ports 30, 31
1 port 31 only
SEG
= 24mA, then I
28-Port LED Display Driver and I/O Expander
4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
Driving Bicolor and Tricolor LEDs
STEP
Applications Information
______________________________________________________________________________________
, is therefore determined by the
I
REGISTER
STEP
STEP
= I
= 24mA / 16 = 1.5mA.
SEG
/ 16
D15
R/ W
R/ W
R/ W
R/ W
R/ W
R/ W
R/ W
R/ W
R/ W
R/ W
R/ W
R/ W
R/ W
R/ W
R/ W
R/ W
D14
Each MAX6957 port can sink a current of 24mA into an
LED with a 2.4V forward-voltage drop when operated
from a supply voltage of at least 3.0V. The minimum
voltage drop across the internal LED drivers is there-
fore (3.0V - 2.4V) = 0.6V. The MAX6957 can sink 28 x
24mA = 672mA when all outputs are operating as LED
segment drivers at full current. On a 3.3V supply, a
MAX6957 dissipates (3.3V - 2.4V)
when driving 28 of these 2.4V forward-voltage drop
LEDs at full current. This dissipation is within the ratings
of the 36-pin SSOP package with an ambient tempera-
ture up to +98°C. If a higher supply voltage is used or
the LEDs used have a lower forward-voltage drop than
2.4V, the MAX6957 absorbs a higher voltage, and the
MAX6957's power dissipation increases.
If the application requires high drive current and high
supply voltage, consider adding a series resistor to
each LED to drop excessive drive voltage off-chip. For
example, consider the requirement that the MAX6957
must drive LEDs with a 2.0V to 2.4V specified forward-
voltage drop, from an input supply range is 5V ±5%
with a maximum LED current of 20mA. Minimum input
supply voltage is 4.75V. Maximum LED series resistor
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
D13
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
COMMAND ADDRESS
D12
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
D11
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
Power Dissipation Issues
D10
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
D9
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
✕
672mA = 0.6W
D8
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
CODE
0x5A
0x5B
0x5C
0x5D
HEX
0x50
0x51
0x52
0x53
0x54
0x55
0x56
0x57
0x58
0x59
0x5E
0x5F
13