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参数资料
| 型号： | AS1118-BQFT |
| 厂商： | ams |
| 文件页数： | 16/21页 |
| 文件大小： | 0K |
| 描述： | IC DRIVER 64LED W/DELAY 24-TQFN |
| 标准包装： | 1 |
| 系列： | * |
AS1118
Datasheet - Ty p i c a l A p p l i c a t i o n
9 Typical Application
Selecting R SET Resistor Value and Using External Drivers
Brightness of the display segments is controlled via R SET . The current that flows between V DD and I SET defines the
current that flows through the LEDs.
Segment current is about 200 times the current in I SET . Typical values for R SET for different segment currents, operat-
ing voltages, and LED voltage drop (V LED ) are given in Table 22 & Table 23 . The maximum current the AS1118 can
drive is 47mA. If higher currents are needed, external drivers must be used, in which case it is no longer necessary
that the devices drive high currents.
Note: The display brightness can also be logically controlled (see Intensity Control Register (0x0A) on page 12) .
Table 22. R SET vs. Segment Current and LED Forward Voltage, V DD = 2.7V & 3.3V & 3.6V
I SEG (mA)
1.5V
V LED
2.0V
1.5V
V LED
2.0V
2.5V
1.5V
2.0V
V LED
2.5V
3.0V
40
30
20
10
5k ?
6.9k ?
10.7k ?
22.2k ?
4.4k ?
5.9k ?
9.6k ?
20.7k ?
6.7k ?
9.1k ?
13.9k ?
28.8k ?
6.4k ?
8.8k ?
13.3k ?
27.7k ?
5.7k ?
8.1k ?
12.6k ?
26k ?
7.5k ?
10.18k ?
15.6k ?
31.9k ?
7.2k ?
9.8k ?
15k ?
31k ?
6.6k ?
9.2k ?
14.3k ?
29.5k ?
5.5k ?
7.5k ?
13k ?
27.3k ?
Table 23. R SET vs. Segment Current and LED Forward Voltage, V DD = 4.0V & 5.0V
I SEG
V LED
V LED
(mA)
1.5V
2.0V
2.5V
3.0V
3.5V
1.5V
2.0V
2.5V
3.0V
3.5V
4.0V
40
8.6k ?
8.3k ?
7.9k ?
7.6k ?
5.2k ?
11.35k ?
11.12k ?
10.84k ? 10.49k ?
10.2k ?
9.9k ?
30
11.6k ?
11.2k ?
10.8k ?
9.9k ?
7.8k ?
15.4k ?
15.1k ?
14.7k ?
14.4k ?
13.6k ?
13.1k ?
20
17.7k ?
17.3k ?
16.6k ?
15.6k ? 13.6k ?
23.6k ?
23.1k ?
22.6k ?
22k ?
21.1k ?
20.2k ?
10
36.89k ? 35.7k ?
34.5k ?
32.5k ? 29.1k ?
48.9k ?
47.8k ?
46.9k ?
45.4k ?
43.8k ?
42k ?
Calculating Power Dissipation
The upper limit for power dissipation (PD) for the AS1118 is determined from the following equation:
PD = (V DD x 5mA) + (V DD - V LED )(DUTY x I SEG x N)
Where:
V DD is the supply voltage.
DUTY is the duty cycle set by intensity register (page 13) .
N is the number of segments driven (worst case is 8)
V LED is the LED forward voltage
I SEG = segment current set by RSET
Dissipation Example:
I SEG = 40mA, N = 8, DUTY = 15/16, V LED = 2.2V at 40mA, V DD = 5V
PD = 5V(5mA) + (5V - 2.2V)(15/16 x 40mA x 8) = 0.865W
Thus, for a QSOP-24 package Θ JA = +88°C/W, the maximum allowed T AMB is given by:
T J,MAX = T AMB + PD x Θ JA = 150°C = T AMB + 0.865W x 88°C/W
In this example the maximum ambient temperature must stay below 73.88°C.
(EQ 1)
(EQ 2)
(EQ 3)
(EQ 4)
www.austriamicrosystems.com/LED-Driver-ICs/AS1118
Revision 1.01
15 - 20
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