EL5825

FN7005 Rev 4.00

Page 9 of 12

June 24, 2005

Channel Outputs

Each of the channel outputs has a rail-to-rail buffer. This

enables all channels to have the capability to drive to within

100mV of the power rails, (see Electrical Characteristics for

details).

When driving large capacitive loads, a series resistor should

be placed in series with the output. (Usually between 5

 and

50

).

Each of the channels is updated on a continuous cycle, the

time for the new data to appear at a specific output will

depend on the exact timing relationship of the incoming data

to this cycle.

The best-case scenario is when the data has just been

captured and then passed on to the output stage

immediately; this can be as short as 40µs. In the worst-case

scenario this will be 320µs, when the data has just missed

the cycle.

When a large change in output voltage is required, the

change will occur in 2 volt steps, thus the requisite number of

timing cycles will be added to the overall update time. This

means that a large change of 16 volts can take between 2.56

milliseconds and 3 milliseconds depending on the absolute

timing relative to the update cycle.

Power Dissipation

With the 30mA maximum continues output drive capability

for each channel, it is possible to exceed the 125°C absolute

maximum junction temperature. Therefore, it is important to

calculate the maximum junction temperature for the

application to determine if load conditions need to be

modified for the part to remain in the safe operation.

The maximum power dissipation allowed in a package is

determined according to:

where:

•

The maximum power dissipation actually produced by the IC

is the total quiescent supply current times the total power

supply voltage and plus the power in the IC due to the loads.

when sourcing, and:

when sinking.

Where:

• i = 1 to total 8

package power dissipation curves provide a convenient way

to see if the device will overheat.

Power Supply Bypassing and Printed Circuit

Board Layout

Good printed circuit board layout is necessary for optimum

performance. A low impedance and clean analog ground

plane should be used for the EL5825. The traces from the

two ground pins to the ground plane must be very short. The

thermal pad of the EL5825 should be connected to the

analog ground plane. Lead length should be as short as

possible and all power supply pins must be well bypassed. A

Application Using the EL5825

In the application drawing, the schematic shows the

interconnect of a pair of EL5825 chips connected to give 8

By using the serial data out pin, it is possible to daisy chain

(cascade) the two chips. In this mode the micro-controller

will send a 32-bit word that will update both the upper and

lower references voltages in one operation. See Application

Drawing 1 for details.



JA

---------------------------------------------

=







+



=





+



=