ISL55001_14 Datasheet, PDF (9/12 Pages) Intersil Corporation – High Supply Voltage 220MHz Unity-Gain Stable Operational Amplifier

ISL55001
For sinking use Equation 3:
n
∑ ^{P D}M A X
=
(V_S+
– V_S- ) × I_SMAX + (V_OUTi – V_S-) ×
i=1
---^V----^O----^U----^T----ⁱ--
R_LOADi
(EQ. 3)
Where:
• V_S+ = Positive supply voltage
• V_S- = Negative supply voltage
• I_SMAX = Maximum quiescent supply current
• V_OUT = Average output voltage of the application
• R_LOAD = Load resistance tied to ground
• I_LOAD = Load current
• n = number of amplifiers (n = 1 for ISL55001)
By setting the two PD_MAX equations (Equations 1, 2 or 3)
equal to each other, we can solve the output current and
R_LOAD to avoid the device overheat.
Power Supply Bypassing Printed Circuit
Board Layout
As with any high frequency device, a good printed circuit
board layout is necessary for optimum performance.
Lead lengths should be as short as possible. The power
supply pin must be well bypassed to reduce the risk of
oscillation. For normal single supply operation, where the
V_S- pin is connected to the ground plane, a single 4.7µF
tantalum capacitor in parallel with a 0.1µF ceramic
capacitor from V_S+ to GND will suffice. This same
capacitor combination should be placed at each supply
pin to ground if split supplies are to be used. In this case,
the V_S- pin becomes the negative supply rail.
Printed Circuit Board Layout
For good AC performance, parasitic capacitance should
be kept to minimum. Use of wire wound resistors should
be avoided because of their additional series inductance.
Use of sockets should also be avoided if possible. Sockets
add parasitic inductance and capacitance that can result
in compromised performance. Minimizing parasitic
capacitance at the amplifier's inverting input pin is very
important. The feedback resistor should be placed very
close to the inverting input pin. Strip line design
techniques are recommended for the signal traces.
Application Circuits
Sallen-Key Low Pass Filter
A common and easy to implement filter taking advantage
of the wide bandwidth, low offset and low power
demands of the ISL55001. A derivation of the transfer
function is provided for convenience (see Figure 25).
Sallen-Key High Pass Filter
Again this useful filter benefits from the characteristics of
the ISL55001. The transfer function is very similar to the
low pass so only the results are presented (see
Figure 26).
R₁
V₁
1kΩ
C₁
1nF
R₂
1kΩ C₂
1nF
R_A
1kΩ
V₂
5V
C₅
1nF
+ ^V+
- _V-
R_B
1kΩ
C₅
1nF
V₃
5V
V_OUT
R₇
1kΩ
Holp = K
wo =
1
R 1C 1 R 2C 2
Q=
(1 − K )
1
R 1C 1 ₊
R 2C 2
R 1C 2 ₊
R 2C 1
R 2C 2
R 1C 1
Holp = ^K
4−K
wo = ²
RC
Q= ²
4− K
FIGURE 25. SALLEN-KEY LOW PASS FILTER
9
FN6200.3
November 3, 2009