ISL55002_06 Datasheet, PDF (9/12 Pages) Intersil Corporation – High Supply Voltage 200MHz Unity-Gain Stable Operational Amplifier

ISL55002
For sourcing:
n
∑ ^PDMAX ^{= V}S ^{× I}SMAX ⁺
(
V_S
–
V_O
U
T
i
)
×
V_{-----O----U----T----i}
R_Li
i=1
For sinking:
n
∑ ^PDMAX ^{= V}S ^{× I}SMAX ^{+ (V}OUTi ^{– V}S^{) × I}LOADi
i=1
Where:
• V_S = Supply voltage
• I_SMAX = Maximum quiescent supply current
• V_OUT = Maximum output voltage of the application
• R_LOAD = Load resistance tied to ground
• I_LOAD = Load current
• N = number of amplifiers (max = 2)
By setting the two PD_MAX equations 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 ISL55002. A derivation of the transfer function is
provided for convenience (See Figure 28).
Sallen Key High Pass Filter
Again this useful filter benefits from the characteristics of the
ISL55002. The transfer function is very similar to the low
pass so only the results are presented (See Figure 29).
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
K = 1+ ^RB
RA
Vo = K ¹ V1
R2C2s + 1
Vo
V1− Vi _{1+ K − V1 +} Vo − Vi _{= 0}
R1
R2
1
C1s
H(s) =
K
R1C1R2C2s² + ((1− K)R1C1+ R1C2 + R21C2)s + 1
H(jw) =
1
1− w ²R1C1R2C2 + jw((1− K)R1C1+ R1C2 + R2C2)
Holp = K
wo =
1
R1C1R2C2
Q=
1
(1− K) ^R1C1 + ^R1C2 +
R2C2 R2C1
R2C2
R1C1
FIGURE 28. SALLEN-KEY LOW PASS FILTER
9
Holp = K
wo = ¹
RC
Q= ¹
3−K
Equations simplify if we let all
components be equal R=C
FN7497.4
July 27, 2006