AS1110 AMSCO [austriamicrosystems AG], AS1110 Datasheet - Page 19

• Manufacturer Part Number: AS1110
• Description: Constant-Current, 16-Channel LED Driver with Diagnostics
• Manufacturer: AMSCO [austriamicrosystems AG]

AS1110
Data Sheet - A p p l i c a t i o n I n f o r m a t i o n
Constant Current
In LED display applications, the AS1110 provides virtually no current variations from channel-to-channel and from
AS1110-to-AS1110. This is mostly due to 2 factors:
Adjusting Output Current
The AS1110 scales up the reference current (I
put port. As shown in
ble to define it as target current (I
Where:
R
V
The magnitude of current (as a function of R
page 7
(R
Package Power Dissipation
The maximum allowable package power dissipation (PD) is determined as:
When 16 output channels are turned on simultaneously, the actual package power dissipation is:
Therefore, to keep P
Where:
T
Delayed Outputs
The AS1110 has graduated delay circuits between outputs. These delay circuits can be found between OUTNn and
constant current block.
The fixed delay time is 20 ns (typ) where OUTN0 has no delay, OUTN1 has 20ns delay, OUTN2 has 40ns delay ...
OUTN15 has 300ns delay. This delay prevents large inrush currents, which reduce power supply bypass capacitor
requirements when the outputs turn on
Switching-Noise Reduction
LED drivers are frequently used in switch-mode applications which normally exhibit switching noise due to parasitic
inductance on the PCB.
Load Supply Voltage
Considering the package power dissipation limits (see EQ 4:6), the AS1110 should be operated within the range of
V
For example, if V
the lowest possible supply voltage or a voltage reducer (V
V
Note: Resistors or zener diodes can be used as a voltage reducer as shown in
www.austriamicrosystems.com
!
!
REXT
J
DS
DS
EXT
EXT
= 150ºC
While I
AS1110 devices.
In the saturation region, the characteristic curve of the output stage is flat
put current can be kept constant regardless of the variations of LED forward voltages (V
= 0.4 to 1.0V.
= (V
is the resistance of the external resistor connected to pin REXT.
).
is the voltage on pin REXT.
shows the relationship curve between the I
LED
OUT
-V
F
≥ 10mA, the maximum current skew is less than ±3% between channels and less than ±6% between
) - V
LED
DROP
D(ACT)
is higher than 5V, V
Figure 3 on page 7
I
REF
.
= V
≤ P
REXT
I
D(MAX)
OUT
OUT TARGET
I
/R
P
OUT TARGET
= {[(T
D(ACT)
, the maximum allowed output current as a function of duty cycle is:
EXT
(see Figure 10 on page 10)
DS
J
(if the other end of R
the output current in the saturation region is extremely flat so that it is possi-
P
-T
= (I
D(MAX)
may be so high that P
AMB
EXT
). I
REF
DD
= I
OUT TARGET
)/R
V
) is around 50.52mA at 372Ω and 25.26mA at 744Ω.
*V
REXT
REF
) set by external resistor (R
= (T
OUT TARGET
TH(J-A)
DD
Revision 1.00
*15 = (1.253V/R
) + (I
J
= 1.253V
-T
]-(I
AMB
DROP
OUT
can be calculated by:
DD
)/R
EXT
of each channel and the corresponding external resistor
*V
*Duty*V
) should be used. The voltage reducer allows
TH(J-A)
DD
D(ACT)
is connected to ground)
)}/V
EXT
DS
DS
> P
*16)
)*15
/Duty/16
D(MAX)
EXT
(see Figure 5 on page
) to sink a current (I
Figure
where V
22.
DS
F
).
= V
LED
OUT
7). Thus, the out-
- V
Figure 3 on
F
) at each out-
. In this case,
19 - 24
(EQ 1)
(EQ 2)
(EQ 3)
(EQ 4)
(EQ 5)
(EQ 6)