STPM32 datasheet(23/89 Pages) STMICROELECTRONICS

23 / 89 page

The converted sigma-delta bitstreams of voltage and current channels are fed to the internal hardwired DSP unit,

which decimates, filters and processes those signals in order to boost the resolution and to yield all necessary

signals for computations.

8.2.3

Clock generator

All the internal timing of the STPM3x is based on the input clock signal, namely 16 MHz. This signal can be

provided in two different ways:

External quartz: the oscillator works with an external crystal

External clock: the XTAL2 pin can be fed by an external 16 MHz clock signal. For specific features of crystal

oscillator or CLKIN signal please refer to Table 4.

The clock generator is powered by the analog supply and is responsible for two tasks. The former delays the turn-

on of some function blocks after POR in order to help a smooth start of external power supply circuitry by keeping

off all major loads. The latter provides all necessary clocks for analog and digital parts.

Figure 26. Different oscillator circuits (a): with quartz; (b): with external source

From the external 16 MHz clock, the entire clock tree is generated. All internal clocks have 50% duty cycle.

Table 10. Clock tree

CLK name

Name

Typical value

Description

Input clock

CLKIN

16 MHz

External clock

Master clock

MCLK

4 MHz

Master root clock

Analog sampling clock

SCLK

4 MHz

OSF of sigma-delta modulators

Decimated clock

DCLK

7.8125 kHz

Sampling frequency of instantaneous voltage and current

values

CLKOUT pin can be used to feed another STPM3x device clock with 16 MHz, when multiple STPM3x are used in

cascade as shown in Figure 27.

A STPM3x can provide clock from CLKOUT pin to one or two cascaded devices for synchronization purposes.

The clock signal routing should guarantee that the signal provided to each STPM3x clock input is compliant with

the specifications in Table 4.

STPM32, STPM33, STPM34

Functional description of the analog part

DS10272 - Rev 13

page 23/89

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