Designing With MSP430F522x and MSP430F521x Devices

The MSP430F522x and MSP430F521x devices support a split supply I/O system that is essential in systems in which the MCU is required to interface with external devices (such as sensors or other processors) that operate at different voltage level compared to the MCU device supply. Additionally, the split supply input voltage range of the F522x and F521x devices starts as low as 1.62 V (see the device data sheet specifications), and this allows for nominal 1.8-V I/O interface without the need for external level translation. This application report describes the various design considerations to keep in mind while designing the F522x and F521x devices in an application.

The application report discusses the new features of F522x and F521x devices, which mainly include the split-supply I/O system and the various digital functions supplied from the split-supply I/O rail.

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1 Split-Supply I/O Systems

For split-supply I/O systems, the split supplies are connected to the V_CC (DVCC and AVCC) and DVIO pins. Supply voltage at DVCC and AVCC pins (V_CC) is used to provide device power, and the supply voltage at the DVIO pin (V_IO) is used to supply the I/O rail of the "DVIO supplied I/O pins". The recommended V_CC supply voltage ranges from 1.8 V to 3.6 V (see note A on Figure 1) and, therefore, these devices do not operate at nominal 1.8 V (that is, 1.8 V ± 10%) supply voltage level. The V_IO supply voltage ranges from 1.62 V to V_CC and is useful in applications that interface with nominal 1.8-V I/O interface (that is, 1.8 V ± 10%).

A. The recommended V_CC supply voltage range of 1.8 V to 3.6 V is applicable to the V_CORE setting of PMMCOREVx = 0. See the device data sheet for the V_CC supply voltage ranges at different V_CORE settings.

B. It is recommended to power AVCC and DVCC from the same source. A maximum difference of 0.3 V between AVCC and DVCC can be tolerated during power-up and operation.

C. See the MSP430F522x, MSP430F521x Mixed-Signal Microcontrollers data sheet for the V_IO supply voltage range.

Figure 1. Split Supply I/O Systems

2 DVIO Supplied I/Os

A group of general-purpose I/Os reside on the DVIO supply domain and are called DVIO supplied I/Os. On the MSP430F522x devices, the following I/Os reside on the DVIO supply domain: Port1 (P1.4 to P1.7), Port2, Port3, Port4, and Port7. The remaining port I/Os reside on the DVCC supply domain.

In the data sheet, these I/O ports are highlighted in the functional block diagrams and are also pointed out in the signal descriptions table for respective I/O pins. Also, the electrical characteristics of I/Os in the DVIO and the DVCC domains are specified separately in MSP430F522x, MSP430F521x Mixed-Signal Microcontrollers.