Datasheet

 2008-2013 Microchip Technology Inc. DS22096B-page 95
MCP453X/455X/463X/465X
FIGURE B-6: Resistor Network Block
Diagram.
The characteristics of the wiper are determined by the
characteristics of the wiper switch at each of the
resistor networks tap points. Figure B-7 shows an
example of a wiper switch. As the device operational
voltage becomes lower, the characteristics of the wiper
switch change due to a lower voltage on the V
G
signal.
Figure B-7 shows an implementation of a wiper switch.
When the transistor is turned off, the switch resistance
is in the Giga s. When the transistor is turned on, the
switch resistance is dependent on the V
G
, V
W
and
V
WCn
voltages. This resistance is referred to as R
W
.
FIGURE B-7: Wiper Switch.
So, looking at the wiper voltage (V
W
) for the
3.0V and 1.8V data gives the graphs in Figure B-8 and
Figure B-9. In the 1.8V graph, as the V
W
approaches
0.8V, the voltage increases nonlinearly. Since V = I * R,
and the current (I
W
) is constant, it means that the
device resistance increased nonlinearly at around
wiper code 160.
FIGURE B-8: Wiper Voltage (V
W
) vs.
Wiper Code (V
DD
= 3.0V, I
W
= 190 µA).
FIGURE B-9: Wiper Voltage (V
W
) vs.
Wiper Code (V
DD
= 1.8V, I
W
= 190 µA).
R
S
A
R
S
R
S
R
S
B
R
W
(1)
W
R
W
(1)
R
W
(1)
R
W
(1)
R
W
(1)
Note 1:The wiper resistance is dependent on
several factors including, wiper code,
device V
DD
, Terminal voltages (on A, B
and W), and temperature.
R
AB
NMOS
PMOS
N
0
N
n-1
N
1
N
n
N
n-2
N
n-3
V
W
V
B
V
A
V
WC(n-2)
DV
G
Note 1: Wiper Resistance (R
W
) depends on the
voltages at the wiper switch nodes
(V
G
, V
W
and V
WCn
).
R
W
(1)
NMOS
PMOS
N
WC
Wiper
V
G
(V
DD
/V
SS
)
“gate”
“gate”
V
W
V
WCn
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0 32 64 96 128 160 192 224 256
Wiper Code
Wiper Voltage (V)
-40C
+25C
+85C
+125C
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
0 32 64 96 128 160 192 224 256
Wiper Code
Wiper Voltage (V)
-40C
+25C
+85C
+125C