MAX6957 MAXIM [Maxim Integrated Products], MAX6957 Datasheet - Page 18

• 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]

value is (4.75V - 2.4V - 0.6V)/0.020A = 87.5Ω. We
choose 82Ω ±2%. Worst-case resistor dissipation is at
maximum toleranced resistance, i.e., (0.020A)
✕
per LED is at maximum input supply voltage, minimum
toleranced resistance, minimum toleranced LED for-
ward-voltage drop, i.e., 0.020 x (5.25V - 2.0V - (0.020A
✕
pation is 920mW, driving all 28 LEDs at 20mA full cur-
rent at once, which meets the 941mW dissipation
ratings of the 36-pin SSOP package.
The MAX6957 operates down to 2V supply voltage
(although the sourcing and sinking currents are not
guaranteed), providing that the MAX6957 is powered
up initially to at least 2.5V to trigger the device's internal
reset, and also that the serial interface is constrained to
10Mbps.
4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
18
Table 11. Even Individual Segment Current Format
1.02) = 34mW. The maximum MAX6957 dissipation
82Ω x 0.98)) = 32.86mW. Worst-case MAX6957 dissi-
LED DRIVE
FRACTION
10/16
11/16
12/16
13/16
14/16
15/16
16/16
______________________________________________________________________________________
1/16
2/16
3/16
4/16
5/16
6/16
7/16
8/16
9/16
R
CURRENT WITH
ISET
CONSTANT
SEGMENT
= 39kΩ (mA)
10.5
13.5
16.5
19.5
22.5
1.5
4.5
7.5
12
15
18
21
24
3
6
9
Low-Voltage Operation
CODE (HEX)
0x12 to 0x1F
0x12 to 0x1F
0x12 to 0x1F
0x12 to 0x1F
0x12 to 0x1F
0x12 to 0x1F
0x12 to 0x1F
0x12 to 0x1F
0x12 to 0x1F
0x12 to 0x1F
0x12 to 0x1F
0x12 to 0x1F
0x12 to 0x1F
0x12 to 0x1F
0x12 to 0x1F
0x12 to 0x1F
ADDRESS
2
✕
(82Ω
D7
See Table 12.
The MAX6957 operates with power-supply voltages of
2.5V to 5.5V. Bypass the power supply to GND with a
0.047µF capacitor as close to the device as possible.
Add a 1µF capacitor if the MAX6957 is far away from
the board's input bulk decoupling capacitor.
D6
D5
D4
Power-Supply Considerations
D3
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
D2
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
D1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
D0
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
HEX CODE
0xXC
0xXD
0xX0
0xX1
0xX2
0xX3
0xX4
0xX5
0xX6
0xX7
0xX8
0xX9
0xXA
0xXB
0xXE
0xXF