3

AN1270.0

September 27, 2006

Finally the center off position provides a means of

connecting a repetitive signal source to the PD input. This is

so the user can observe power-down enable/disable timing.

An important note to remember when using the PD - BNC:

1. Place the switch in center-off position.

2. The PD input is referenced to VCC/VEE. The low

amplitude of the PD input must match the VEE voltage.

The high amplitude must be close to VCC.

Comparator Threshold Rails

Each comparator has two thresholds. CVA/CVB. The data

sheet explains the operation of these analog inputs.

However, it should be mentioned that while the ISL55142

(Dual) and ISL55143 (QUAD) comparators have separate

threshold inputs for each comparator, the evaluation boards

have all CVA inputs tied to single CVA_BUS. Accordingly, all

CVB inputs are tied to a single CVB_BUS.

Initial Power-Up

Please refer to the device specification for power-up

sequencing and current requirements. Also note that the

frequency of operation and number of comparators will

determine the current needed. There are graphs in the

specification regarding current characteristics.

When first powering up the device, set all power bus inputs

to minimum current levels needed for quiescent operation.

Check the device out statically with DC inputs on the VINP

pins and observe that the QA/QB outputs toggle when the

VINP voltage crosses the CVA and CVB thresholds.

Once static observations check out, you can then increase

power current limits for VCC/VEE and VOH/VOL and apply

higher frequency inputs to the VINP pins.

Layout Information

All evaluation boards have complete silk-screen information

regarding test points, jumpers and component placements.

The silk-screen on the board you receive will provide

up-to-date layout information.

Schematic Information

Schematics are drawn with physical location in mind. Any

changes in electrical circuitry will be updated in this

document as needed.

Included in the following pages are three schematics.

ISL55141 single comparator device, ISL55142 dual

comparator and ISL55143 quad comparator device. The

Evaluation boards are laid out for the TSSOP packages for

the ISL55141 and ISL55142, while the ISL55143 is the QFN

package. Please refer to the device specification for part

numbers/options for these and other package ordering.

Bill of Material

A bill of material of the ISL55142 evaluation board is

included on page 6. It provides sources for special

components such as the BNC connectors and banana jacks.

All other parts are QPL standard passive components. Refer

to device specification (FN6230) when ordering

replacements for actual ISL55141, ISL55142 or ISL55143

devices.

FIGURE 7. ISL55142 AND ISL55143 COMPARATOR

THRESHOLD CVA/CVB INPUTS ARE TIED

TOGETHER TO EITHER THE CVA_BUS OR

CVB_BUS.

QA0

2

QB0

3

QA1

4

VINP2

20

VINP0

26

CVB0

27

QB1

5

CVA2

19

QA2

6

QB2

7

QA3

8

QB3

9

CVA1

22

VINP1

23

CVA0

25

CVB1

24

CVB2

21

ISL55143_QFN

CVB_BUS

CVA_BUS

Application Note 1270