LCD PANEL VCOM
參數(shù)資料
型號: AD5251BRU1-RL7
廠商: Analog Devices Inc
文件頁數(shù): 18/28頁
文件大?。?/td> 0K
描述: IC DCP DUAL 1K 64POS 14TSSOP T/R
標準包裝: 1,000
接片: 64
電阻(歐姆): 1k
電路數(shù): 2
溫度系數(shù): 標準值 650 ppm/°C
存儲器類型: 非易失
接口: I²C(設備位址)
電源電壓: 2.7 V ~ 5.5 V,±2.25 V ~ 2.75 V
工作溫度: -40°C ~ 85°C
安裝類型: 表面貼裝
封裝/外殼: 14-TSSOP(0.173",4.40mm 寬)
供應商設備封裝: 14-TSSOP
包裝: 帶卷 (TR)
Data Sheet
AD5251/AD5252
Rev. D | Page 25 of 28
APPLICATIONS INFORMATION
LCD PANEL VCOM ADJUSTMENT
Large LCD panels usually require an adjustable VCOMvoltage
centered around 6 V to 8 V with ±1 V swing and small steps
adjustment. This example represents common DAC appli-
cations where the window of adjustments is small and centered
at any level. High voltage and high resolution DACs can be
used, but it is far more cost-effective to use low voltage digital
potentiometers with level shifting, such as the AD5251 or
AD5252, to achieve the objective.
Assume a VCOM voltage requirement of 6 V ± 1 V with a ±20 mV
step adjustment, as shown in Figure 44. The AD5252 can be
configured in voltage divider mode with an op amp gain. With
±20% tolerance accounted for by the AD5252, this circuit can
still be adjusted from 5 V to 7 V with an 8 mV/step in the
worst case.
VDD
U1
U2
VCOM
+5V
R2
10k
R4
6k
R3
18.5k
R5
1k
R1
350k
C1
2.2pF
B
AD5252
+14.4V
±20%
±1%
6V
± 1V
V+
V–
03823-0-044
Figure 44. Apply 5 V Digital Potentiometer AD5251 in a 6 V ± 1 V Application
CURRENT-SENSING AMPLIFIER
The dual-channel, synchronous update, and channel-to-channel
resistance matching characteristics make the AD5251/AD5252
suitable for current-sensing applications, such as LED
brightness control. In the circuit shown in Figure 45, when
RDAC1 and RDAC3 are programmed to the same settings, it
can be shown that
(
)
REF
N
o
V
D
V
+
=
1
2
(8)
As a result, the current through a sense resistor connected
between V1 and V2 can be determined.
The circuit can be programmed for use with systems that require
different sensitivities. If the op amp has very low offset and low
bias current, the major source of error comes from the digital
potentiometer channel-to-channel resistance mismatch, which
is typically 0.15%. The circuit accuracy is about 9 bits, which is
adequate for LED control and other general-purpose applications.
U1
V1
RSENSE
0.1k
RDAC1
10k
RDAC3
10k
B
AD5252
AD8628
U2
VO
VREF
+5V
V+
V–
03823-0-045
V2
Figure 45. Current-Sensing Amplifier
ADJUSTABLE HIGH POWER LED DRIVER
Figure 46 shows a circuit that can drive three or four high power
LEDs. The ADP1610 is an adjustable boost regulator that provides
adequate headroom and current for the LEDs. Because its FB pin
voltage is 1.2 V, the digital potentiometer AD5252 and the op amp
form an average gain of 12 feedback networks that servo the
sensing and feedback voltages. As a result, the voltage across
RSET is regulated around 0.1 V, depending on the AD5252’s
setting. An adjustable LED current is
SET
R
LED
R
V
I
SET
=
(9)
RSET should be small enough to conserve power, but large enough
to limit the maximum LED current. R3 should be used in parallel
with the AD5252 to limit the LED current to an achievable range.
SD
SW
FB
COMP
SS
RT
GND
IN
PWM
CC
390pF
CSS
10nF
RO
100k
RSET
0.25k
10k
W
B
A
C8
0.1
F
AD5252
ADP1610
VOUT
AD8591
U3
U1
U2
U1
+5V
V+
V–
03823-0-046
R3
200
R2
1.1k
R1
100
C3
10
F
C2
10
F
D1
D2
D3
L1
10
F
Figure 46. High Power, Adjustable LED Driver
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