for V
參數(shù)資料
型號(hào): MCP4441-104E/ML
廠商: Microchip Technology
文件頁(yè)數(shù): 93/100頁(yè)
文件大小: 0K
描述: IC DGTL POT 129TAPS QUAD 20QFN
標(biāo)準(zhǔn)包裝: 91
接片: 129
電阻(歐姆): 100k
電路數(shù): 4
溫度系數(shù): 標(biāo)準(zhǔn)值 150 ppm/°C
存儲(chǔ)器類型: 非易失
接口: I²C(設(shè)備位址)
電源電壓: 2.7 V ~ 5.5 V
工作溫度: -40°C ~ 125°C
安裝類型: 表面貼裝
封裝/外殼: 20-VFQFN 裸露焊盤
供應(yīng)商設(shè)備封裝: 20-QFN 裸露焊盤(4x4)
包裝: 管件
MCP444X/446X
DS22265A-page 92
2010 Microchip Technology Inc.
Figure B-3 and Figure B-4 show the wiper resistance
for VDD voltages of 5.5, 3.0, 1.8 Volts. These graphs
show that as the resistor ladder wiper node voltage
(VWCn) approaches the VDD/2 voltage, the wiper
resistance increases. These graphs also show the
different resistance characteristics of the NMOS and
PMOS transistors that make up the wiper switch. This
is demonstrated by the wiper code resistance curve,
which does not mirror itself around the mid-scale code
(wiper code = 128).
So why are the RW graphs showing the maximum
resistance at about mid-scale (wiper code = 128) and
the RBW graphs showing the issue at code 160?
This requires understanding low-voltage transistor
characteristics as well as how the data was measured.
FIGURE B-3:
Wiper Resistance (RW) vs.
Wiper Code and Temperature
(VDD = 5.5V, IW = 900 A; VDD = 3.0V,
IW = 480 A).
FIGURE B-4:
Wiper Resistance (RW) vs.
Wiper Code and Temperature
(VDD = 1.8V, IW = 260 A).
The method in which the data was collected is
important to understand. Figure B-5 shows the
technique that was used to measure the RBW and RW
resistance. In this technique, Terminal A is floating and
Terminal B is connected to ground. A fixed current is
then forced into the wiper (IW) and the corresponding
wiper voltage (VW) is measured. Forcing a known
current through RBW (IW) and then measuring the
voltage difference between the wiper (VW) and
Terminal A (VA), the wiper resistance (RW) can be
calculated, see Figure B-5. Changes in IW current will
change the wiper voltage (VW). This may affect the
device’s wiper resistance (RW).
FIGURE B-5:
RBW and RW Measurement.
Figure B-6 shows a block diagram of the resistor
network where the RAB resistor is a series of 256 RS
resistors. These resistors are polysilicon devices. Each
wiper switch is an analog switch made up of an NMOS
and PMOS transistor. A more detailed figure of the
wiper switch is shown in Figure B-7. The wiper
resistance is influenced by the voltage on the wiper
switches nodes (VG, VW and VWCn). Temperature also
influences the characteristics of the wiper switch, see
The NMOS transistor and PMOS transistor have
different characteristics. These characteristics, as well
as the wiper switch node voltages, determine the RW
resistance at each wiper code. The variation of each
wiper switch’s characteristics in the resistor network is
greater then the variation of the RS resistors.
The voltage on the resistor network node (VWCn) is
dependent upon the wiper code selected and the
voltages applied to VA, VB and VW. The wiper switch VG
voltage to VW or VWCn voltage determines how strongly
the transistor is turned on. When the transistor is
weakly turned on, the wiper resistance RW will be high.
When the transistor is strongly turned on, the wiper
resistance (RW) will be in the typical range.
20
40
60
80
100
120
140
160
180
200
220
0
64
128
192
256
Wiper Code
Resistance
()
-40C @ 3.0V
+25C @ 3.0V
+85C @ 3.0V
+125C @ 3.0V
-40C @5.5V
+25C @ 5.5V
+85C @ 5.5V
+125C @ 5.5V
20
520
1020
1520
2020
0
64
128
192
256
Wiper Code
Resistance
()
-40C @ 1.8V
+25C @ 1.8V
+85C @ 1.8V
+125C @ 1.8V
A
B
W
IW
VW
floating
RBW = VW/IW
VA
VB
RW = (VW-VA)/IW
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