MCP607 查看數據表（PDF） - Microchip Technology
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MCP607 Datasheet PDF : 30 Pages
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MCP606/7/8/9
After selecting RISO for your circuit, double-check the
resulting frequency response peaking and step
response overshoot. Modify RISO’s value until the
response is reasonable. Bench evaluation and simula-
tions with the MCP606/7/8/9 SPICE macro model are
helpful.
4.4 MCP608 Chip Select (CS)
The MCP608 is a single op amp with Chip Select (CS).
When CS is pulled high, the supply current drops to
50 nA (typ.) and flows through the CS pin to VSS. When
this happens, the amplifier output is put into a high-
impedance state. By pulling CS low, the amplifier is
enabled. If the CS pin is left floating, the amplifier may
not operate properly. Figure 1-1 shows the output
voltage and supply current response to a CS pulse.
4.5 Supply Bypass
With this family of operational amplifiers, the power
supply pin (VDD for single-supply) should have a local
bypass capacitor (i.e., 0.01 µF to 0.1 µF) within 2 mm
for good high-frequency performance. It also needs a
bulk capacitor (i.e., 1 µF or larger) within 100 mm to
provide large, slow currents. This bulk capacitor can be
shared with other nearby analog parts.
4.6 PCB Surface Leakage
In applications where low input bias current is critical,
Printed Circuit Board (PCB) surface-leakage effects
need to be considered. Surface leakage is caused by
humidity, dust or other contamination on the board.
Under low humidity conditions, a typical resistance
between nearby traces is 1012Ω. A 5V difference would
cause 5 pA of current to flow, which is greater than the
MCP606/7/8/9 family’s bias current at 25°C (1 pA, typ.).
The easiest way to reduce surface leakage is to use a
guard ring around sensitive pins (or traces). The guard
ring is biased at the same voltage as the sensitive pin.
An example of this type of layout is shown in Figure 4-4.
VIN-
VIN+
VSS
Guard Ring
FIGURE 4-4:
Example Guard Ring Layout
for Inverting Gain.
1. Non-inverting Gain and Unity-gain Buffer:
a) Connect the non-inverting pin (VIN+) to the
input with a wire that does not touch the
PCB surface.
b) Connect the guard ring to the inverting input
pin (VIN–). This biases the guard ring to the
common mode input voltage.
2. Inverting Gain and Transimpedance Gain
(convert current to voltage, such as photo
detectors) amplifiers:
a) Connect the guard ring to the non-inverting
input pin (VIN+). This biases the guard ring
to the same reference voltage as the op
amp (e.g., VDD/2 or ground).
b) Connect the inverting pin (VIN–) to the input
with a wire that does not touch the PCB
surface.
4.7 Application Circuits
4.7.1
LOW-SIDE BATTERY CURRENT
SENSOR
The MCP606/7/8/9 op amps can be used to sense the
load current on the low-side of a battery using the
circuit in Figure 4-5. In this circuit, the current from the
power supply (minus the current required to power the
MCP606) flows through a sense resistor (RSEN), which
converts it to voltage. This is gained by the the amplifier
and resistors, RG and RF.Since the non-inverting input
of the amplifier is at the load’s negative supply (VLM),
the gain from RSEN to VOUT is RF/RG.
VOUT
=
VL
M
+
IL
R
S
(
EN
RF
⁄
RG
)
IL
2.5V
to
5.5V
RG
RF
5 kΩ 50 kΩ
RSEN
10Ω
MCP606
To Load
(VLP)
VOUT
To Load
(VLM)
FIGURE 4-5:
Sensor.
Low Side Battery Current
Since the input bias current and input offset voltage of
the MCP606 are low, and the input is capable of swing-
ing below ground, there is very little error generated by
the amplifier. The quiescent current is very low, which
helps conserve battery power. The rail-to-rail output
makes it possible to read very low currents.
DS11177D-page 12
© 2005 Microchip Technology Inc.
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