2-24 | Theory of Operation: VOCON Board |
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The audio and power supply IC (GCAP II IC) has many functions. It supplies most of the voltages used on the VOCON board, while external linear regulators supply 5 Vdc and 1.55 Vdc. It also has microphone audio amplifiers, switching between internal and accessory microphones, multiplexing capability for receive and transmit audio, filtering, voltage regulators, a real-time clock (RTC), and the audio CODEC. The audio CODEC performs analog-to-digital and digital-to-analog conversions on audio signals. The GCAP IC also has an analog/digital converter (ADC), which is used to monitor volume setting and battery voltage. The GCAP II IC is programmed by the dual-core processor.
The audio pre-amplifier and the audio PA condition the received audio signal from the analog output of the CODEC from the GCAP IC before the audio is routed to the speaker. The dual EEPOT sets the gain of the microphone signal. The audio PA is sourced from the battery, and both of these devices are programmed by the dual-core processor.
2.5.2.2.1 GCAP II IC U501
The GCAP II IC is a mixed-signal (analog and digital) IC that provides control, audio, and voltage regulation functionality. It comes in a 100-pin, ball-grid array (BGA) package with 0.8 mm pitch solder balls. The GCAP II IC is supplied with switched battery voltage GCAP_B+ (R581).
Voltage Regulation
The GCAP II IC contains several voltage regulators that are used in the design of the VOCON board: VSW1, VSW2, and V2. The VSW1 regulator is a programmable switching regulator that uses the switched battery voltage as its input on pin PSRC1. The output voltage of VSW1 (R502) is programmable by the dual-core processor U401 through the SPI bus. The initial output of VSW1 is
3.2volts, which is then programmed to 3.8 volts. The VSW1 voltage is supplied to the RF Interface connector P201 pin 15 and to the input pins of the VSW2 and V2 regulators.
The VSW2 regulator is a SPI programmable switching regulator that uses VSW1 as its input on pin PSRC2. The initial output of VSW2 (R501) is 2.2 volts, which is then programmed to 1.875 volts (referred to as 1.8 volts throughout this document). The VSW2 voltage is supplied to the dual-core processor (core voltage and the EIM voltage), the SRAM U403, the Flash memory U402, and the display module connector J301
The V2 regulator is a SPI programmable linear regulator that uses VSW1 as its input on pin VIN2. The initial output of V2 (R560) is 2.775 volts, which is then programmed to 2.9 volts. The V2 voltage is supplied to the dual-core processor (I/O ring - SPI, BBP, SAP, UART, GPIO, etc.), the digital- support IC U301, the EEPOT U509, the display module connector J301, and the many discrete components that interface with the dual-core processor and the digital-support IC.
MCU Interface
The GCAP II IC has a four-wire, SPI connection to the dual-core processor (SPI B). The SPI B clock is connected to the SPI_CLK pin (test point SCKB). The SPI B MOSI line is connected to the SPI_DW pin (test point MOSIB). The SPI B MISO line is connected to the SPI_DR pin (test point MISOB). The GCAP SPI B chip-select signal is connected to the CE pin (R539). Through this interface, the dual-core processor can program the voltage regulators, the CODEC, the transmit and receive audio filters and amplifiers, as well as read information from the ADC and the real-time clock.
The GCAP II IC has an 8-bit ADC with general-purpose six channels and four voltage-monitoring channels. The six general-purpose analog-to-digital (A/D) channels are assigned to the display backlight button on the control head (AD0), the monitor volume (AD5); the two-position toggle switch (AD1); the OPT_SEL_IN (AD2) (for determining accessory attachment), VOCON board ID (AD3), and RF board ID (AD4). Battery voltage is also monitored by the ADC. The dual-core processor activates and reads the A/D values through the SPI bus.
