Datasheet

13
®
PGA204/205
FIGURE 5. Voltage Swing of A
1
and A
2
.
Input-overload often produces an output voltage that appears
normal. For example, consider an input voltage of +20V on
one input and +40V on the other input will obviously exceed
the linear common-mode range of both input amplifiers.
Since both input amplifiers are saturated to the nearly the
same output voltage limit, the difference voltage measured
by the output amplifier will be near zero. The output of the
PGA204/205 will be near 0V even though both inputs are
overloaded.
INPUT PROTECTION
The inputs of the PGA204/205 are individually protected for
voltages up to ±40V. For example, a condition of –40V on
one input and +40V on the other input will not cause
damage. Internal circuitry on each input provides low series
impedance under normal signal conditions. To provide
equivalent protection, series input resistors would contribute
excessive noise. If the input is overloaded, the protection
circuitry limits the input current to a safe value (approxi-
mately 1.5mA). The typical performance curve “Input Bias
Current vs Common-Mode Input Voltage” shows this input
current limit behavior. The inputs are protected even if no
power supply voltage is present.
FIGURE 6. Switch-Selected PGIA.
A
1
A
2
A
3
12
11
10
25kΩ25kΩ
25kΩ25kΩ
13
5
14
16
4
V+
PGA204
PGA205
Ref
V
O
Feedback
Digitally Selected
Feedback Network
1
V
O1
15
A
1
A
0
Digital
Ground
9 8
V
O2
V–
V
D
2
V
D
2
V
CM
V
CM
–
G • V
D
2
V
CM
+
G • V
D
2
Over-Voltage
Protection
Over-Voltage
Protection
SWITCH
POSITION
V+
47kΩ47kΩ
D1, D2: IN4148, IN914, etc.
A
0
A
1
A
BC
D
X
V
IN
–
V
IN
+
PGA204 PGA205
GAIN
A
B
C
D
1
10
100
1000
1
2
4
8
PGA204
PGA205
The information provided herein is believed to be reliable; however, BURR-BROWN assumes no responsibility for inaccuracies or omissions. BURR-BROWN assumes
no responsibility for the use of this information, and all use of such information shall be entirely at the user’s own risk. Prices and specifications are subject to change
without notice. No patent rights or licenses to any of the circuits described herein are implied or granted to any third party. BURR-BROWN does not authorize or warrant
any BURR-BROWN product for use in life support devices and/or systems.