STW5098T datasheet(17/85 Pages) STMICROELECTRONICS

17 / 85 page

STw5098

Functional description

17/85

Functional description

4.1

Naming convention

The STw5098 is composed of two identical entities, with their respective set of control

registers.

Regarding the pin labelling, a pin name preceded by 1 refers to entity 1 and a pin name

preceded by 2 refers to entity 2 (ie.g. 1SCLK, 2SCLK). In the following sections, no

distinction is made between the two entities when it is not relevant. Consequently, the 1 and

2 prefixes for entities 1 and 2 respectively are omitted. The same naming convention applies

to the control registers (CRxxx).

4.2

Power supply

STw5098 can have different supply voltages for different blocks, to optimize performance,

power consumption and connectivity. See

Section 9.2 on page 59 for voltage definition.

The correct sequence to apply supply voltage is to set first (and unset last) the digital I/O

supply (VCCIO). The other supply voltages can be set in any order and can be disconnected

individually, if needed. Disconnection does not cause any harm to the device and no extra

current is pulled from any supply during this operation. Moreover if a voltage conflict is

detected, like VCCA < VCC (not allowed), simply all blocks connected to VCCA are set to

power down and no extra current is pulled from supply.

When VCCIO is set and VCC (digital supply) is not set, all the digital output pins are in high

impedance state, while the digital inputs are disconnected to avoid power consumption for

any input voltage value between GND and VCCIO. Before VCC is disconnected the device

has to be reset (SWRES bit in CR30).

When the analog supply (VCCA) is set and VCC is not set, all the analog inputs are in high

impedance state.

The two sets of control registers are powered by VCC pins (digital supply) so if these pins

are disconnected all the information stored in control registers is lost. When the digital

supply voltage is set, a power-on-reset (POR) circuit sets all the registers content to the

default value and then generates IRQ signals writing 1 in bits PORMSK end POREV in

CR31 and CR32 respectively for both entities.

All supplies must be on during operation.

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