TC35679FSG-002

2018-01-17

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4.7. ADC

4.7.1.

Features

TC35679 has 6 ch of 10 bits ADCs for battery monitoring, analog inputs from external sensors, for example. The ADC has the

following features.



5 ch for analog inputs (shared with GPIO pins)



1 ch for VBAT voltage monitor

Note: The reference input is internally connected to VBAT, and the analog input is to built-in VDDCORE2 output.

Please refer to 4.7.2 for how to calculate voltage value.



Maximum conversion rate: 1 MS/s

4.7.2.

Descriptions

The ADC has 10 bits conversion accuracy and can work for input voltages from 0 V to 3.6 V (VBAT). It has 6 ch of analog inputs, and

the ch0 is connected to VDDCORE2 output, and the ch1 to ch5 are shared with GPIO pins.

When a battery is used as power source, the reference voltage can slide over time because the battery is connected as reference

voltage. In that case, the VDDCORE2 output voltage connected to ch0 can be used as a reference voltage. The input voltage to ch1

to ch5 is converted by the reference voltage of ch0 and the converted value is used to calculate a correct digital value by the CPU.

The following shows the conversion method of the input voltage.

VoltageAat time T can be calculated as follows

(1) VDDCORE2 output voltage (VDDCORE2) on Ch0 should be converted by theADC. The converted digital value is X.

(2) The analog signal on Ch1 is converted and the converted digital value is Y.

(3) When the absolute value of the analog signal on Ch1 is defined asA(V), VDDCORE2 (V) / A(V) = X / Y. So,

A(V) = VDDCORE2 (V) × Y / X

Calculation example:

Suppose ch0 (for ex. VDDCORE2 output is 1.1 V) is converted to 0x0134, and ch1 (measurement target) is converted to

0x0188, the absolute voltage at ch1A(V) is given by 1.1 × 0x0188 / 0x0134 = 1.1 × 392 / 308 = 1.4 (V).

Figure 4-20 shows conceptual of voltage conversion.

3.3V

VDDCORE2

voltage

A[V]

(1)=X

(2)=Y

[t]

[V]

Time[T]

VREF

Figure 4-20 Voltage conversion concept

The ADC converts input voltage of ch selected by register settings. When a conversion has finished, the CPU detects it by the interrupt

or register polling, and then reads the conversion results. The maximum sampling rate depends on software load on the CPU.

Note: The numerical values are expressed as follows.

Hexadecimal number:

0xABC