Motore di ricerca datesheet componenti elettronici |
|
AD7769AN Scheda tecnica(PDF) 8 Page - Analog Devices |
|
AD7769AN Scheda tecnica(HTML) 8 Page - Analog Devices |
8 / 16 page AD7769 –8– REV. A CIRCUIT DESCRIPTION Analog Inputs and Outputs The AD7769 provides the analog-to-digital and digital-to-analog conversion functions required between the microcontroller and the servo power amplifier in digital servo systems. It is intended primarily for closed loop head positioning in Winchester disk drives, but may also be used for microstepping in drives with stepper motor head positioning or other servo applications. The AD7769 contains a high speed, 8-bit, sampling ADC with two input channels and two 8-bit DACs with output buffer amplifi- ers. A unique feature of the AD7769 is the input and output sig- nal conditioning circuitry that allows the analog input and output voltages to be referred to a point other than analog ground. The input range and offset of the ADC, the output swing and offset of the DACs may be adjusted independently by the application of ground-referenced, positive control voltages, VBIAS (ADC), VSWING (ADC), VBIAS (DAC) and VSWING (DAC). Thus, for example, the peak-to-peak output swing of the DACs could be set to 3 V above and 3 V below a bias voltage of 5 V. Figures 5 and 6 show the transfer functions of the ADC and DACs and their relationship to VBIAS and VSWING. The Figure 5. ADC Transfer Function Figure 6. DAC Transfer Function midpoint code of the ADC, 80 Hex (10000000 Binary), occurs at an input voltage equal to VBIAS. The input FSR of the ADC is equal to 2 VSWING, so that the Plus Full-Scale code transition (FE to FF Hex) occurs at a voltage equal to VBIAS + VSWING –1.5 LSBs and the Minus Full-Scale code transition (01 to 00 Hex) occurs at a voltage VBIAS – VSWING +0.5 LSBs. The transfer function of the DACs bears a similar relationship to VBIAS and VSWING. The DAC output voltage for code 80 Hex (10000000 binary) is equal to VBIAS, while FF Hex (11111111 binary) gives an output voltage of VBIAS + VSWING –1 LSB (Plus Full-Scale) and 00 Hex gives an output voltage of VBIAS – VSWING (Minus Full-Scale). The ability to refer input and output signals to some voltage other than ground is of particular importance in disk drive ap- plications. Typically, only +5 V digital and +12 V analog supply voltages are available, and the analog signals are often referred to a voltage around half the analog supply. Driving the Analog Inputs and Reference Inputs The analog inputs, VINA and VINB, must be driven from low output impedance sources, such as from op amps. In addition, VBIAS (ADC) must be driven from a similar type low impedance source (e.g., voltage reference). Op amps are not required to drive the VSWING (ADC), VBIAS (DAC) and VSWING (DAC) inputs as these are high impedance inputs (200 nA typical input current) that feed into on-chip buffer amplifiers. The reference voltages for these inputs can be derived using suitable resistor divider networks. The analog reference available in the disk drive system can be used to set the bias voltage of the AD7769, and could also be at- tenuated to provide the reference for the input and output swing as shown in Figure 7. The same bias voltage would generally (though not necessarily) be used for the ADC and the DACs, though the input and output ranges might be different. Figure 7. Typical Analog Connections to the AD7769 ADC Conversion Cycle Figure 8 shows the operating waveforms for a conversion cycle. On the rising edge of WR, the conversion cycle starts with the acquisition and tracking of the selected ADC channel, VINA or VINB. The analog input voltage is held 50 ns (typically) after the fourth falling edge of the input CLK following a conversion start. If tD in Figure 8 is greater than 150 ns, then the falling edge of the input CLK will be seen as the first falling clock edge. If tD is less than 150 ns, the first falling clock edge to be recog- nized will not occur until one cycle later. |
Codice articolo simile - AD7769AN |
|
Descrizione simile - AD7769AN |
|
|
Link URL |
Privacy Policy |
ALLDATASHEETIT.COM |
Lei ha avuto il aiuto da alldatasheet? [ DONATE ] |
Di alldatasheet | Richest di pubblicita | contatti | Privacy Policy | scambio Link | Ricerca produttore All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |