ADA4817-2ACPZ-R2 datasheet(15/24 Pages) AD

15 / 24 page

ADA4817-1/ADA4817-2

Rev. 0 | Page 15 of 24

Figure 43 shows the small signal frequency response of the

ADA4817-2 at a gain of 2 vs. CF. At first no CF was used to show

the peaking then two other values of 0.5 pF and 1 pF were used

to show how to reduce the peaking or even eliminate it. As

shown in Figure 43, if the power consumption is a factor in

the system, then using a larger feedback capacitor is acceptable

as long as a feedback capacitor is used across it to control the

peaking. However, if the power consumption is not an issue,

then a lower value feedback resistor such as 100 Ω, would not

require any additional feedback capacitance to maintain flatness

and lower peaking.

POWER-DOWN OPERATION

The ADA4817-1/ADA4817-2 are equipped with separate

power-down pins (PD) pins for each amplifier. This allows the

user the ability to reduce the quiescent supply current when

an amplifier is inactive from 2 mA to 19 mA. The power-down

threshold levels are derived from the voltage applied to the +VS

pin. In ±5 V supply application, the enable voltage is greater

than +4 V, and in a ±3 V supply application, the enable voltage

is greater than +2 V. However, the amplifier is powered down

whenever the voltage applied to the PD pin is 3 V below +VS.

If the PD pin is not to be used, it is best to connect it to the

positive supply.

Table 7. Power-Down Voltage Control

PD Pin

–3

–6

–9

0.1

100

10k

FREQUENCY (MHz)

RF = 348Ω

G = 2

VS = 10V

VOUT = 100mV p-p

RL = 100Ω

CF = 1pF

CF = 0.5pF

NO CF

±5 V

+3 V, −2 V

Not active

>4 V

>2 V

Active

<2 V

<0 V

CAPACITIVE FEEDBACK

Due to package variations and pin-to-pin parasitic between the

single and the dual, the ADA4817-2 has a little more peaking

then the ADA4817-1, especially at a gain of 2. The best way to

tame the peaking is to place a feedback capacitor across the

feedback resistor.

Figure 43. Small Signal Frequency Response vs. Feedback Capacitor

(ADA4817-2)

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