LM8342SD datasheet(15/16 Pages) NSC

15 / 16 page

Typical Application (Continued)

TABLE 4. Overview Resistor Values for Different R

SET

Settings at AV

DD = 15V

DD = 15V (VCOM Level = 7.5 V)

SET =10k

Ω

SET =45k

Ω

∆V

COM

(V)

(

Ω)

(

Ω)

∆V

COM

(V)

(

Ω)

(

Ω)

±0.5

25k

28.6k

±0.5

113k

129k

±1

47.1k

61.5k

±1

212k

277k

±1.5

66.7k

100k

±1.5

300k

450k

±2

84.2k

146k

±2

379k

655k

±2.5

100k

200k

±2.5

450k

900k

±3

114k

267k

±3

514k

1.2M

EVALUATION SYSTEM

For the LM8342 a complete evaluation system is available,

including two boards. Figure 10 gives a schematic represen-

tation.

•

LM8342 Evaluation Board

This board demonstrates the functionality of the LM8342

using the I

2C compatible interface for communication.

The LM8342 can easily be demonstrated in 2 applica-

tions:

— Programmable current sink

— Programmable V

COM level driver

•

LM8342 Programmer Board

This test board has dedicated functionality for communi-

cating with the LM8342, using the I

2C compatible inter-

face. This board can operate in two different modes:

— Write mode: The digitized value of a potentiometer

setting is written to the LM8342. The user can select

on the programmer board to write the data to the

— Read mode: The board reads the stored values from

the LM8342’s EEPROM and presents this data onto a

3-digit display.

LAYOUT RECOMMENDATIONS

A proper layout is necessary for optimum performance of the

LM8342. A low impedance and proper ground plane (free of

disturbances) is recommended, since a current of up to 10

mA can flow with HF contents during programming. The

traces from the GND pin to the ground plane should be as

short as possible. It is recommended to place decoupling

capacitors close to the V

DD and AVDD pins. Connections of

these decoupling capacitors to the ground plane should be

short.

As SET is a sensitive input, crosstalk to that pin should be

prevented. Special care should be taken when routing the

interface connections. The signals on the serial interface can

be more than 60 dB larger than the equivalent LSB at the

SET input pin. Crosstalk between the interface bus and R

SET

results in disturbance of the output current I

OUT

of the

LM8342.

For applications requiring a low output current (using high

values for R

SET in combination with low DAC settings) spe-

cial attention should be paid to the parasitic capacitance

PAR) parallel to RSET. For CPAR larger than tens of pF, a

small (<1 LSB) unwanted ripple at the output current might

be obtained. It is recommended to place the R

SET resistor

close to the LM8342, in combination with a good board

layout to reduce this parasitic capacitance.

20139232

FIGURE 10. LM8342 Evaluation System

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