MSP430FG6626 Datasheet, PDF (156/171 Pages) Texas Instruments – Mixed-Signal Microcontrollers

MSP430FG6626, MSP430FG6625
MSP430FG6426, MSP430FG6425
SLAS874 – MAY 2015
www.ti.com
7.2.2.3 Detailed Design Procedure
Operational amplifiers are a diverse and useful tool in many applications. Some common configurations
that might prove to be useful to the user are transimpedance amplifiers to convert currents to voltage,
voltage-gain amplifiers, and buffering configurations. For more information about how to design these
circuits along with other common configurations, see the following application notes.
• Op Amps for Everyone Design Guide (SLOD006)
• Handbook of Operational Amplifier Applications (SBOA092)
• Understanding Basic Analog – Ideal Op Amps (SLAA068)
• An Applications Guide for Op Amps (SNOA621)
7.2.2.4 Layout Guidelines
Components that are shown in the partial schematic (see Figure 7-8) should be placed as close as
possible to the respective device pins. Avoid long traces, because they add additional parasitic
capacitance, inductance, and resistance on the signal. Avoid routing analog input signals close to a high-
frequency pin (for example, a high-frequency PWM), because the high-frequency switching can be
coupled into the analog signal. When possible, use internal connections to other modules to limit the
potential of error introduction.
7.2.3 RTC_B With Battery Backup System
If not using a separate battery backup supply in the system, see Section 4.5 for VBAT and VBAK
connections.
7.2.3.1 Partial Schematic
C_BAK
VBAK
–+
VBAT
BAT
(see Note A)
A. BAT can be a battery or super-capacitor. See Section 5.5.8 for specifications.
Figure 7-9. OA Partial Schematic
7.2.3.2 Retaining an Accurate Real-Time Clock (RTC) Through Main Supply Interrupts
The RTC_B module with Battery Backup System is designed to keep an accurate RTC during main supply
interruptions and during low-power modes. For more details on when the Backup Battery System
engages, see the Battery Backup System chapter in the MSP430x5xx and MSP430x6xx Family User's
Guide (SLAU208). See Using the MSP430 RTC_B Module With Battery Backup Supply (SLAA665) for
more information and example code on how to keep an accurate RTC through power loss.
7.2.3.3 Charging Super-Capacitors With Built-In Resistive Charger
In applications that use a super-capacitor instead of a battery for secondary supply, the charging circuit
functionality of the Battery Backup System can be used to charge the super-capacitor. The resistive
charger circuit connects VBAT to DVCC with selectable resistor values found in Section 5.5.8. This means
that if DVCC is not present, you cannot use this feature to charge a super-capacitor connected to VBAT.
The CTSD16 module can be used to sense the voltage level on VBAT divided by a factor of three. Typical
values during VBAT sensing are listed in Section 5.5.8. Channel A8 of the CTSD16 is routed internally for
this. See the CTSD16 chapter of the MSP430x5xx and MSP430x6xx Family User's Guide (SLAU208) for
more information. The BAKADC bit in the BAKCTL register must also be enabled for this feature to
156 Applications, Implementation, and Layout
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