STPM098C datasheet(42/110 Pages) STMICROELECTRONICS

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3.7.2

Internal clock monitor (ICM)

The correct operation and the precision of the internal synchronization signal is safety relevant and therefore

STPM098C implements a monitoring unit to detect abnormal deviation of the clock signal frequency.

The monitoring unit is based on the use of two oscillators and two monitor chains (a main one and an auxiliary

one) to avoid common-cause failures. The main oscillator feeds, by default, the internal logic as system clock,

while the auxiliary oscillator is used for diagnosis purpose only.

Each monitor chain compares the other clock period, the first one samples CLK1 by means of CLK2 and the

second one samples CLK2 by means of CLK1.

If ∆f1=|(fCLK1 - fCLK2)/fCLK2| ≥ ICM_err_th: the flag CLK_MISMATCH is set. Internal reset is triggered.

If ∆f2=|(fCLK2 - fCLK1)/fCLK1| ≥ ICM_err_th: the flag CLK_MISMATCH is set.

If TCLK1 ≥ ICM_timeout_th: the flags INT_RST and CLK1_TIME_OUT are set. Internal reset is triggered.

If TCLK2 ≥ ICM_timeout_th: the flag CLK2_TIME_OUT is set.

If one of the previous conditions is verified the device state moves to SAFE STATE. The error flags remain set

until the failure condition is removed and the flags are cleared by PMBus™ command or VR1_EN or VR2_EN.

The correct level of the clock monitor is safety relevant, thus a self-check procedure is implemented on its

monitor.

Table 33. Internal clock monitor electrical characteristics

Symbol

Parameter

Test condition Min Typ Max Unit

Notes

ICM_err_th

ICM frequency mismatch threshold

accuracy

Application information

ICM_timeout_th ICM timeout accuracy

μs

Application information

3.8

Ground loss monitor (GLM)

STPM098C implements one ground reference pin GND dedicated to the low power internal analog/digital circuitry.

For EMI robustness GND pin is internally split in two GND reference PADs: AGND (ground reference for analog

circuitry supplied from VCC and VREF2) and DGND (ground reference for digital circuitry supplied by VREF1).

AGND is connected to the GND ESD ring by means of a direct metal connection and biases the substrate through

SUB plugs placed all around the IC border.

STPM098C implements a monitoring unit to detect disconnection affecting ground references.

If VGND_DIG-VGND_ANA ≥ VTH_GND occurs for an interval longer than T_glm_loss_flt, the DGND_LOSS flag

is set.

If VGND_ANA-VGND_DIG ≥ VTH_GND occurs for an interval longer than T_glm_loss_flt, the AGND_LOSS flag

is set.

The correct operation ground loss monitor stage is safety relevant and then a self-check procedure is

implemented.

Table 34. GLM electrical characteristics

Symbol

Parameter

Test condition

Min

Typ

Max

Unit

Notes

GLM_th

GLM detection threshold VTH_GND

0.24

0.4

0.55

T_glm_loss_flt

GLM filter time

CLK_SSM_EN = 0

1.25

1.5

Digital filter

STPM098C

Functional description

DS14440 - Rev 1

page 42/110

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