ISL24202

6

FN7587.0

March 15, 2011

Application Information

circuit using a mechanical potentiometer, and the equivalent

circuit replacement using the ISL24202. Having a digital counter

interface enables automatic, digital flicker minimization during

production test and alignment. After programming, the counter

interface is not needed again - the ISL24202 automatically powers

The ISL24202 uses a digitally controllable potentiometer (DCP),

with 256 steps of resolution (Figure 4) to change the current

drawn at the OUT pin, which then changes the voltage created by

buffered by an external amplifier (A2) to generate a buffered output

The amount of current sunk is controlled by the setting of the

DCP, which is recalled at power-up from the ISL24202’s internal

EEPROM. The EEPROM is typically programmed during panel

manufacture. As noted in the “Electrical Specifications” section

10.8V for EEPROM programming, but will work in normal

operation down to 4.5V after the EEPROM has been

programmed, with no additional EEPROM writing.

DCP (Digitally Controllable Potentiometer)

The DCP controls the voltage that ultimately controls the SET

current. Figure 4 shows the relationship between the register

value and the DCP’s tap position. Note that a register value of 0

selects the first step of the resistor string. The output voltage of

the DCP is given in Equation 1:

Output Current Sink

Figure 5 shows the schematic of the OUT current sink. The

forms a voltage-controlled current source, with the voltage

determined by the DCP setting.

that can be pulled from the OUT node. The relationship between

maximum register value of 255 into Equation 2, resulting in

Equation 3:

Equation 2 can also be used to calculate the unit sink current

step size per Register Code, resulting in Equation 4:

FIGURE 3. MECHANICAL ADJUSTMENT REPLACEMENT

SET

ISL24202

OUT

A2

RegisterValue 1

+

256

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

⎝⎠

20

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

⎝⎠

⎛⎞

=

(EQ. 1)

FIGURE 4. SIMPLIFIED SCHEMATIC OF DCP

19R

R

0

1

2

255

254

253

252

251

REGISTER VALUE

20

FIGURE 5. CURRENT SINK CIRCUIT

SET

OUT

Q1

A1

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

RegisterValue 1

+

256

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

⎝⎠

20

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

⎝⎠

⎛⎞

1

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

⎝⎠

⎛⎞

==

(EQ. 2)

()

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

=

(EQ. 3)

256

() 20

() R

SET

()

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

=

(EQ. 4)