Electronic Components Datasheet Search |
|
HA5025EVAL Datasheet(PDF) 5 Page - Intersil Corporation |
|
HA5025EVAL Datasheet(HTML) 5 Page - Intersil Corporation |
5 / 11 page 5 Application Information Performance The amplifiers comprising the HFA1305 are high frequency current feedback amplifiers. As such, they are sensitive to feedback capacitance which destabilizes the op amp and causes overshoot and peaking. Unfortunately, the standard triple op amp pinout places the amplifier’s output next to its inverting input, thus making the package capacitance an unavoidable parasitic feedback capacitor. Optimum Feedback Resistor Although a current feedback amplifier’s bandwidth dependency on closed loop gain isn’t as severe as that of a voltage feedback amplifier, there can be an appreciable decrease in bandwidth at higher gains. This decrease may be minimized by taking advantage of the current feedback amplifier’s unique relationship between bandwidth and RF. All current feedback amplifiers require a feedback resistor, even for unity gain applications, and RF, in conjunction with the internal compensation capacitor, sets the dominant pole of the frequency response. Thus, the amplifier’s bandwidth is inversely proportional to RF. The HFA1305 design is optimized for RF = 510Ω (SOIC) at a gain of +2. Decreasing RF decreases stability, resulting in excessive peaking and overshoot (Note: Capacitive feedback causes the same problems due to the feedback impedance decrease at higher frequencies). However, at higher gains the amplifier is more stable so RF can be decreased in a trade-off of stability for bandwidth. The table below lists recommended RF values for various gains, and the expected bandwidth. For good channel-to- channel gain matching, it is recommended that all resistors (termination as well as gain setting) be ±1% tolerance or better. Non-inverting Input Source Impedance For best operation, the DC source impedance seen by the non-inverting input should be ≥ 50Ω. This is especially important in inverting gain configurations where the non- inverting input would normally be connected directly to GND. Pulse Undershoot The HFA1305 utilizes a quasi-complementary output stage to achieve high output current while minimizing quiescent supply current. In this approach, a composite device replaces the traditional PNP pulldown transistor. The composite device switches modes after crossing 0V, resulting in added distortion for signals swinging below ground, and an increased undershoot on the negative portion of the output waveform (see Figure 6). This undershoot isn’t present for small bipolar signals, or large positive signals (see Figure 4 and Figure 5). PC Board Layout The frequency response of this amplifier depends greatly on the amount of care taken in designing the PC board. The use of low inductance components such as chip resistors and chip capacitors is strongly recommended, while a solid ground plane is a must! Attention should be given to decoupling the power supplies. A large value (10 µF) tantalum in parallel with a small value (0.1 µF) chip capacitor works well in most cases. Terminated microstrip signal lines are recommended at the input and output of the device. Capacitance, parasitic or planned, connected to the output must be minimized, or isolated as discussed in the next section. Care must also be taken to minimize the capacitance to ground at the amplifier’s inverting input (-IN). The larger this capacitance, the worse the gain peaking, resulting in pulse overshoot and eventual instability. To reduce this capacitance the designer should remove the ground plane under traces connected to -IN, and keep connections to -IN as short as possible. An example of a good high frequency layout is the Evaluation Board shown in Figure 3. Driving Capacitive Loads Capacitive loads, such as an A/D input, or an improperly terminated transmission line will degrade the amplifier’s phase margin resulting in frequency response peaking and possible oscillations. In most cases, the oscillation can be avoided by placing a resistor (RS) in series with the output prior to the capacitance. Figure 1 details starting points for the selection of this resistor. The points on the curve indicate the RS and CL combinations for the optimum bandwidth, stability, and settling time, but experimental fine tuning is recommended. Picking a point above or to the right of the curve yields an overdamped response, while points below or left of the curve indicate areas of underdamped performance. RS and CL form a low pass network at the output, thus limiting system bandwidth well below the amplifier bandwidth of 560MHz. By decreasing RS as CL increases (as illustrated in the curve), the maximum bandwidth is obtained without sacrificing stability. In spite of this, bandwidth still decreases as the load capacitance increases. OPTIMUM FEEDBACK RESISTOR GAIN (ACL) RF (Ω) SOIC BANDWIDTH (MHz) SOIC -1 360 420 +1 464 (+RS = 649) 375 +2 510 560 +5 200 330 +10 180 140 HFA1305 |
Similar Part No. - HA5025EVAL |
|
Similar Description - HA5025EVAL |
|
|
Link URL |
Privacy Policy |
ALLDATASHEET.NET |
Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Contact us | Privacy Policy | Link Exchange | Manufacturer List 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 |