Data Sheet AS8118

Revision 1.8, 15-Feb-05

Page 21 of 30

Digital readout uses the threshold of the comparator internal to the AS8118. Thus, the result, which can be observed on the

CAL pin, is the same as that used internally by the AS8118. Digital readout does NOT allow the quality of the ‘burn’ to be

evaluated.

Analog readout does allow for the verification of the analog value of the zener diodes. With analog readout, the quality of the

‘burn’ can be verified.

In order to verify the ‘burn’ process, an ‘analog readout’ of the zener diodes voltages has to be performed as the last step

after calibration. This can be done during the ‘read’ process, which may be started during calibration mode. The goal is to

verify that burned diodes show a voltage level of not more than 0.5V during the analog readout and the ‘unburned’ diodes a

voltage level of more than 2.4V.

Digital Readout

The AS8118 offers the customer the ability to read the PROM data. For example, it may be necessary to examine if a device

has been calibrated already and what value is correctly stored in the PROM. For the read mode the same two digital inputs

(TM and DIRO) are used as for ‘testwrite’ and ‘burn’. As can be seen in the following timing diagram the read mode is

selected by setting DIRO=1 while there is a rising edge on TM. (This assumes that one of the 3 modes has been completed

or the chip has just been powered up, i.e. the chip expects to enter a new mode.)

The following timing diagram shows the digital readout of the zener diodes:

TM

DIRO

PROG

69

68

67

66

0

1

2

define

read

mode

f1

t2

t3

(DIRO=1)

High

Low

High

Low

High

CAL

High

Low

end

read

Low

Note:

1.

High and Low refers to VDD and VSS respectively.

2.

In this case, the term ‘digital’ means that there is an on-chip comparator, which decides on the values of the bits, 0 or 1,

After starting read mode with each rising edge on DIRO one of the PROM cells is selected. Its content is stored in a separate

internal flip-flop, the output of which can be watched on pin CAL (only during read!). With one additional rising edge on TM

the read mode is left and pin CAL shows the normal pulse output again.

Important: The bits displayed on CAL are the inverse of the PROM contents, i.e. they have to be inverted to match with the

previous PROM contents table.

Important timings are:

f1: Maximum read frequency, for reliable reading this should not be higher than 100kHz.

t2: Delay between the two rising edges: >100ns

t3: Depending on the loading on pin CAL the delay between rising edge on TM and change of data on CAL may vary. A

typical value is 50 ns.