9
FN6200.3
November 3, 2009
For sinking use Equation
3:Where:
VS+ = Positive supply voltage
VS- = Negative supply voltage
ISMAX = Maximum quiescent supply current
VOUT = Average output voltage of the application
RLOAD = Load resistance tied to ground
ILOAD = Load current
n = number of amplifiers (n = 1 for ISL55001)
By setting the two PDMAX equations (Equations 1, 2 or 3) equal to each other, we can solve the output current and
RLOAD 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
VS- pin is connected to the ground plane, a single 4.7F
tantalum capacitor in parallel with a 0.1F ceramic
capacitor from VS+ 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 VS- 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
(EQ. 3)
PD
MAX
(V
S+
V
S- )
–
I
SMAX
V
OUTi
V
–
S
-
()
i1
=
n
∑
V
OUTi
R
LOADi
---------------------
×
+
×
=
K
Q
RC
wo
K
Holp
C
R
C
R
C
R
C
R
C
R
C
R
K
Q
C
R
C
R
wo
K
Holp
=
=
+
=
4
2
4
)
1
(
1
2
1
2
1
2
1
2
1
FIGURE 25. SALLEN-KEY LOW PASS FILTER
+
-
V+
V-
V2
5V
C5
1nF
VOUT
R7
1kΩ
V3
5V
R1
1kΩ
R2
1kΩ C2
1nF
V1
C1
1nF
C5
1nF
RA
1kΩ
RB
1kΩ
ISL55001