Motor de Búsqueda de Datasheet de Componentes Electrónicos |
|
AD9243 Datasheet(PDF) 11 Page - Analog Devices |
|
AD9243 Datasheet(HTML) 11 Page - Analog Devices |
11 / 24 page AD9243 REV. A –11– REFERENCE OPERATION The AD9243 contains an onboard bandgap reference that pro- vides a pin-strappable option to generate either a 1 V or 2.5 V output. With the addition of two external resistors, the user can generate reference voltages other than 1 V and 2.5 V. Another alternative is to use an external reference for designs requiring enhanced accuracy and/or drift performance. See Table II for a summary of the pin-strapping options for the AD9243 reference configurations. Figure 26 shows a simplified model of the internal voltage reference of the AD9243. A pin-strappable reference amplifier buffers a 1 V fixed reference. The output from the reference amplifier, A1, appears on the VREF pin. The voltage on the VREF pin determines the full-scale input span of the A/D. This input span equals, Full-Scale Input Span = 2 × VREF A2 5k 5k 5k 5k LOGIC 7.5k LOGIC A1 5k 1V TO A/D CAPT VREF DISABLE A2 DISABLE A1 REFCOM SENSE CAPB AD9243 Figure 26. Equivalent Reference Circuit The voltage appearing at the VREF pin as well as the state of the internal reference amplifier, A1, are determined by the volt- age appearing at the SENSE pin. The logic circuitry contains two comparators which monitor the voltage at the SENSE pin. The comparator with the lowest set point (approximately 0.3 V) controls the position of the switch within the feedback path of A1. If the SENSE pin is tied to REFCOM, the switch is con- nected to the internal resistor network thus providing a VREF of 2.5 V. If the SENSE pin is tied to the VREF pin via a short or resistor, the switch is connected to the SENSE pin. A short will provide a VREF of 1.0 V while an external resistor network will provide an alternative VREF between 1.0 V and 2.5 V. The other comparator controls internal circuitry which will disable the reference amplifier if the SENSE pin is tied AVDD. Dis- abling the reference amplifier allows the VREF pin to be driven by an external voltage reference. The actual reference voltages used by the internal circuitry of the AD9243 appear on the CAPT and CAPB pins. For proper operation when using the internal or an external reference, it is necessary to add a capacitor network to decouple these pins. Figure 27 shows the recommended decoupling network. This capacitive network performs the following three functions: (1) along with the reference amplifier, A2, it provides a low source impedance over a large frequency range to drive the A/D inter- nal circuitry, (2) it provides the necessary compensation for A2, and (3) it bandlimits the noise contribution from the reference. The turn-on time of the reference voltage appearing between CAPT and CAPB is approximately 15 ms and should be evalu- ated in any power-down mode of operation. 0.1 F 10 F 0.1 F 0.1 F CAPT CAPB AD9243 Figure 27. Recommended CAPT/CAPB Decoupling Network The A/D’s input span may be varied dynamically by changing the differential reference voltage appearing across CAPT and CAPB symmetrically around 2.5 V (i.e., midsupply). To change the reference at speeds beyond the capabilities of A2, it will be necessary to drive CAPT and CAPB with two high speed, low noise amplifiers. In this case, both internal amplifiers (i.e., A1 and A2) must be disabled by connecting SENSE to AVDD and VREF to REFCOM and the capacitive decoupling network removed. The external voltages applied to CAPT and CAPB must be 2.5 V + Input Span/4 and 2.5 V – Input Span/4 respec- tively in which the input span can be varied between 2 V and 5 V. Note that those samples within the pipeline A/D during any reference transition will be corrupted and should be discarded. Table II. Reference Configuration Summary Reference Input Span (VINA–VINB) Operating Mode (V p-p) Required VREF (V) Connect To INTERNAL 2 1 SENSE VREF INTERNAL 5 2.5 SENSE REFCOM INTERNAL 2 ≤ SPAN ≤ 5 AND 1 ≤ VREF ≤ 2.5 AND R1 VREF AND SENSE SPAN = 2 × VREF VREF = (1 + R1/R2) R2 SENSE AND REFCOM EXTERNAL 2 ≤ SPAN ≤ 51 ≤ VREF ≤ 2.5 SENSE AVDD (NONDYNAMIC) VREF EXT. REF. EXTERNAL 2 ≤ SPAN ≤ 5 CAPT and CAPB SENSE AVDD (DYNAMIC) Externally Driven VREF REFCOM EXT. REF. CAPT EXT. REF. CAPB |
Número de pieza similar - AD9243 |
|
Descripción similar - AD9243 |
|
|
Enlace URL |
Política de Privacidad |
ALLDATASHEET.ES |
¿ALLDATASHEET es útil para Ud.? [ DONATE ] |
Todo acerca de Alldatasheet | Publicidad | Contáctenos | Política de Privacidad | Intercambio de Enlaces | Lista de Fabricantes 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 |