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2.7 Constant Current
In LED display application, LXY28161 provides nearly no
variation in current from channel to channel and from IC to IC. This
can be achieved by:
1) The typical current variation between channels is less than ±3%,
and that between IC is less than ±6%.
2) In addition, the output current can be kept constant regardless of
LED forward voltages. This guarantees LED to be performed on the same
brightness as user’s specification.
2.8 Setting Output Current
The output current (IOUT) is set by an external resistor, Rext. The
default relationship between IOUT and Rext is:
VR-EXT=1.26V ;
IOUT=(VR-EXT/Rext) x 15.5
Rext is the resistance of the external connected to R-EXT
terminal
VR－EXT is its voltage
The output current is about 21mA when Rext=910Ω and 10.8mA
when Rext=1800Ω
2.9 Delay Time of Staggered Output
LXY28161 has a built-in staggered circuit to perform delay
mechanism. 16 channels are divided to four groups. Each output port
has 25nS delay time, so that the instant current from the power line
will be lowered.
2.10 Package Power Dissipation
The maximum allowable package power dissipation is determined as
PD(max)=(Tj–Ta)/Rth(j-a).
When 16 output channels are turned on simultaneously, the actual
package power dissipation is
PD(act)=(IDDxVDD)+(IOUTxDutyxVDSx16).
Therefore, to keep PD (act)≤PD (max), the allowable maximum output
current as a function of duty cycle is:
IOUT={[(Tj–Ta)/Rth(j-a)]–(IDDxVDD)}/ (DutyxVDSx16), （Tj=150°C）
The maximum power dissipation, PD(max)=(Tj–Ta)/Rth(j-a), decreases
as the ambient temperature increases. So the LXY28161 must work in
Safe Operation Area.
S
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2.11 Usage of Thermal Pad
The PCB area L2xW2 is 4 times of the IC’s area L1xW1.
