L99LD21 datasheet(46/73 Pages) STMICROELECTRONICS

46 / 73 page

SPI functional description

L99LD21

46/73

DS11130 Rev 5

5.4.4

Customer test and trimming procedure description

General description

The writing procedure is performed connecting the two terminals of the anti-fuse capacitor

at 15 V and ground respectively. This is achieved by providing 15V on VS battery pin.

After this phase, the capacitor is burnt and behaves like a resistance; its value (the residual

resistance) strictly depends on the effectiveness of the burning procedure. During physical

reading operation, the residual resistance is compared with a fixed threshold. If the residual

resistance is greater than threshold a bit 0 is given, and the OTP cell is considered

unwritten, otherwise a bit 1 is given and the OTP cell is considered written.

Blank check reading is executed to verify that all anti-fuses are unwritten after fabrication,

while margin mode, usually performed immediately after the burning process, is used to

verify if burned cells are properly written. Executing a blank-check reading after all writing

operations have been completed allows verifying that unwritten cells haven’t been degraded

by burning processes.

Recommended test flow

In Figure 10 and in Table 28 the recommended testing procedure is shown and described.

Testing procedure starts with a blank check read, to verify that all anti-fuse rows are

unwritten. After this operation, it is possible to select the bits to be written and to start

programming. Writing operation should be performed up to 3 times. At the end of

programming, a reading procedure should be performed in Margin Mode.

At the end of the test, it is strongly recommended executing a blank-check read in order to

verify that unwritten cells haven’t been degraded.

Table 27 summarizes the writing test conditions.

Note:

An external capacitance must be applied between VS and GROUND pins.

Table 27. Writing test conditions

Symbol

Parameter

Conditions

Min

Typ

Max

Unit

15 V supply

IHV

HV current during

programming

—

Temperature

-40

150

°C

—

External capacitance

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