L9679P datasheet(43/279 Pages) STMICROELECTRONICS

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DS11627 Rev 7

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L9679P

Start-up and power control

278

6.5.2

ER CAP ESR measurement

The IC contains the capability to perform a measurement of the equivalent series resistance

of energy reserve capacitor. In this case the discharge current is 10 times higher to create a

voltage difference proportional to the ER CAP ESR. The voltage measurement and

conversion is automatically executed once the user requires the ESR measurement through

the LPDIAGREQ register.

Figure 17. ER ESR measurement block diagram

After an ESR measurement is requested, the IC executes an internal automatic sequence to

take three voltage measurements at the ER node, toggling the ER discharge current source

on and off as shown in Figure 18. The test lasts for TESR_DIAG. After this time has elapsed,

the results can be retrieved by reading the DIAGCTRL_x registers. The three ER voltage

measurements are provided at the same time in DIAGCTRLA, DIAGCTRLB and

DIAGCTRLC registers. During the execution of the ESR measurement no other activity on

ADC is allowed. The user must ensure no other ADC requests are queued to be executed at

the same time of ESR measurement. The ESR diagnostic, once initiated, will continue

without interruption even if the device enters in ER State because of a battery loss event.

ER_DISCHARGE

Level shifter

S & H

GNDA

ER Cap

ESR

GND_ADC

VER

ADC

10-bit

leak

GAPGPS02263

L9679P データシート(PDF) 43 Page - STMicroelectronics