Moteur de recherche de fiches techniques de composants électroniques |
|
OP285GS Fiches technique(PDF) 7 Page - Analog Devices |
|
OP285GS Fiches technique(HTML) 7 Page - Analog Devices |
7 / 16 page REV. A OP285 –7– APPLICATIONS Short-Circuit Protection The OP285 has been designed with inherent short-circuit protection to ground. An internal 30 Ω resistor, in series with the output, limits the output current at room temperature to ISC+ = 40 mA and ISC- = –90 mA, typically, with ±15 V supplies. However, shorts to either supply may destroy the device when excessive voltages or current are applied. If it is possible for a user to short an output to a supply, for safe operation, the out- put current of the OP285 should be design-limited to ±30 mA, as shown in Figure 1. RFB FEEDBACK RX 332 A1 VOUT A1 = 1/2 OP285 – + Figure 1. Recommended Output Short-Circuit Protection Input Over Current Protection The maximum input differential voltage that can be applied to the OP285 is determined by a pair of internal Zener diodes connected across the inputs. They limit the maximum differ- ential input voltage to ± 7.5 V. This is to prevent emitter-base junction breakdown from occurring in the input stage of the OP285 when very large differential voltages are applied. How- ever, in order to preserve the OP285’s low input noise voltage, internal resistance in series with the inputs were not used to limit the current in the clamp diodes. In small-signal applications, this is not an issue; however, in industrial appli- cations, where large differential voltages can be inadvertently applied to the device, large transient currents can be made to flow through these diodes. The diodes have been designed to carry a current of ± 8 mA; and, in applications where the OP285’s differential voltage were to exceed ± 7.5 V, the resis- tor values shown in Figure 2 safely limit the diode current to ± 8 mA. A1 909 A1 = 1/2 909 – + Figure 2. OP285 Input Over Current Protection Output Voltage Phase Reversal Since the OP285’s input stage combines bipolar transistors for low noise and p-channel JFETs for high speed performance, the output voltage of the OP285 may exhibit phase reversal if either of its inputs exceed its negative common-mode input voltage. This might occur in very severe industrial applications where a sensor or system fault might apply very large voltages on the inputs of the OP285. Even though the input voltage range of the OP285 is ±10.5 V, an input voltage of approximately –13.5 V will cause output voltage phase reversal. In inverting amplifier configurations, the OP285’s internal 7.5 V input clamping diodes will prevent phase reversal; however, they will not prevent this effect from occurring in noninverting applications. For these applications, the fix is a simple one and is illustrated in Figure 3. A 3.92 k Ω resistor in series with the noninverting input of the OP285 cures the problem. RFB* VIN RS 3.92k VOUT RL 2k *RFB IS OPTIONAL + – Figure 3. Output Voltage Phase Reversal Fix Overload or Overdrive Recovery Overload or overdrive recovery time of an operational amplifier is the time required for the output voltage to recover to a rated output voltage from a saturated condition. This recovery time is important in applications where the amplifier must recover quickly after a large abnormal transient event. The circuit shown in Figure 4 was used to evaluate the OP285’s overload recovery time. The OP285 takes approximately 1.2 µs to recover to VOUT = +10 V and approximately 1.5 µs to recover to V OUT = –10 V. VIN 4V p-p @100 Hz VOUT RL 2.43k A1 = 1/2 OP285 R2 10k R1 1k 1 2 3 A1 RS 909 Figure 4. Overload Recovery Time Test Circuit Driving the Analog Input of an A/D Converter Settling characteristics of operational amplifiers also include the amplifier’s ability to recover, i.e., settle, from a transient output current load condition. When driving the input of an A/D converter, especially successive-approximation converters, the amplifier must maintain a constant output voltage under dynamically changing load current conditions. In these types of converters, the comparison point is usually diode clamped, but it may deviate several hundred millivolts resulting in high frequency modulation of the A/D input current. Amplifiers that exhibit high closed-loop output impedances and/or low unity-gain crossover frequencies recover very slowly from output load current transients. This slow recovery leads to linearity errors or missing codes because of errors in the instantaneous input voltage. Therefore, the amplifier chosen for this type of application should exhibit low output impedance and high unity-gain bandwidth so that its output has had a chance to settle to its nominal value before the converter makes its comparison. The circuit in Figure 5 illustrates a settling measurement circuit for evaluating the recovery time of an amplifier from an output load current transient. The amplifier is configured as a follower with a very high speed current generator connected to its output. In this test, a 1 mA transient current was used. As shown in Figure 6, the OP285 exhibits an extremely fast recovery time of 139 ns to 0.01%. Because of its high gain-bandwidth product, high open-loop gain, and low output impedance, the OP285 is ideally suited to drive high speed A/D converters. |
Numéro de pièce similaire - OP285GS |
|
Description similaire - OP285GS |
|
|
Lien URL |
Politique de confidentialité |
ALLDATASHEET.FR |
ALLDATASHEET vous a-t-il été utile ? [ DONATE ] |
À propos de Alldatasheet | Publicité | Contactez-nous | Politique de confidentialité | Echange de liens | Fabricants 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 |