L99LD20 datasheet(37/61 Pages) STMICROELECTRONICS

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DS11366 Rev 3

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L99LD20

SPI functional description

4.4.4

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 8 and in Table 26 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 25 summarizes the writing test conditions.

Note:

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

Table 25. 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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