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AD7889 Folha de dados(PDF) 18 Page - Analog Devices |
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AD7889 Folha de dados(HTML) 18 Page - Analog Devices |
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18 / 40 page  AD7879/AD7889 Data Sheet Rev. D | Page 18 of 40 AUX/VBAT/GPIO PIN The AUX/VBAT/GPIO pin on the AD7879/AD7889 can be programmed as an auxiliary input to the ADC, as a battery monitoring input or as a GPIO. To select the auxiliary measurement, set the ADC channel address to 011 (Bits[14:12] in Control Register 1, Address 0x01). To select a battery measurement, set the ADC channel address to 010. To select the GPIO function, set Bit 13 in Control Register 2 (Address 0x02) to 1. AUXILIARY INPUT The AD7879/AD7889 have an auxiliary analog input, AUX. When the auxiliary input function is selected, the signal on the AUX pin (AUX/VBAT/GPIO) is connected directly to the ADC input. This channel has a full-scale input range from 0 V to VCC. The ADC channel address for AUX is 011 (Bits[14:12] in Control Register 1, Address 0x01), and the result is stored in the AUX/VBAT result register (Address 0x0C). BATTERY INPUT The AD7879/AD7889 can monitor battery voltages from 0.5 V to 5 V when the BAT measurement is selected. Figure 28 shows a block diagram of a battery voltage monitored through the VBAT pin. The voltage to the VCC pin (VCC/REF) of the AD7879/AD7889 is maintained at the desired supply voltage via the dc-to-dc converter, and the input to the converter is monitored. This voltage on VBAT is divided by 4 internally, so that a 5 V battery voltage is presented to the ADC as 1.25 V. To conserve power, the divider circuit is on only during the sampling of a voltage on VBAT. Note that the possible maximum input is 5 V. The ADC channel address for VBAT is 010 (Bits[14:12] in Control Register 1, Address 0x01), and the result is stored in the AUX/VBAT result register (Address 0x0C). ADC 0.125V TO 1.25V SW VBAT VCC 12kΩ 4kΩ DC-TO-DC CONVERTER BATTERY 0.5V TO 5V Figure 28. Block Diagram of Battery Measurement Circuit The maximum battery voltage that the AD7879/AD7889 can measure changes when a different reference voltage is used. The maximum voltage that is measurable is VCC × 4 because this voltage gives a full-scale output from the ADC. Calculate the battery voltage using the following formula: VBAT (V) = ((Register Value) × VCC × 4)/4095 LIMIT COMPARISON The AUX measurement and the battery measurement can be compared with high and low limits stored on chip. An out of limit result generates an alarm output at the INT pin (PENIRQ/ INT/DAV) when the INT function is enabled. The high limit for both channels is stored in the AUX/VBAT high limit register (Address 0x04), and the low limit is stored in the AUX/VBAT low limit register (Address 0x05). After a measurement from either AUX or VBAT is taken, it is compared with the high and low limits. The out of limit comparison sets a status bit in Control Register 3. Separate status bits for the high limit and the low limit indicate which limit was exceeded. The interrupt sources can be masked by clearing the corresponding enable bit in Control Register 3. GPIO The AD7879/AD7889 have one general-purpose logic input/output pin, GPIO (AUX/VBAT/GPIO). To enable GPIO, set Bit 13 in Control Register 2 to 1. If this bit is set to 0, the AUX/VBAT function is active on the pin. If the GPIO is not enabled, the other GPIO configuration bits have no effect. The GPIO data bit is Bit 12 in Control Register 2. Direction (Bit 11, Control Register 2, Address 0x02) Bit 11 sets the direction of the GPIO pin (AUX/VBAT/GPIO). When GPIO DIR = 0, the pin is an output. Setting or clearing the GPIO data bit (Bit 12 in Control Register 2) outputs a value on the GPIO pin. When GPIO DIR = 1, the pin is an input. An input value on the GPIO pin sets or clears the GPIO data bit (Bit 12 in Control Register 2). GPIO data register bits are read-only when GPIO DIR = 1. Polarity (Bit 10, Control Register 2, Address 0x02) When GPIO POL = 0, the GPIO pin is active low. When GPIO POL = 1, the GPIO pin is active high. How this bit affects the GPIO operation also depends on the GPIO DIR bit. If GPIO POL = 1 and GPIO DIR = 1, a 1 at the input pin sets the corresponding GPIO data register bit to 1. A 0 at the input pin clears the corresponding GPIO data bit to 0. If GPIO POL = 1 and GPIO DIR = 0, a 1 in the GPIO data register bit puts a 1 on the corresponding GPIO output pin. A 0 in the GPIO data register bit puts a 0 on the GPIO output pin. If GPIO POL = 0 and GPIO DIR = 1, a 1 at the input pin sets the corresponding GPIO data bit to 0. A 0 at the input pin clears the corresponding GPIO data bit to 1. If GPIO POL = 0 and GPIO DIR = 0, a 1 in the GPIO data register bit puts a 0 on the corresponding GPIO output pin. A 0 in the GPIO data register bit puts a 1 on the GPIO output pin. |
Nº de peça semelhante - AD7889 |
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Descrição semelhante - AD7889 |
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