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参数资料
| 型号： | MCP795W22T-I/ST |
| 厂商： | Microchip Technology |
| 文件页数： | 8/13页 |
| 文件大小： | 0K |
| 描述： | IC RTCC 2KB EE WD/EVENT 14TSSOP |
| 标准包装： | 2,500 |
| 类型： | 时钟/日历 |
| 特点： | 警报，EEPROM，闰年，方波输出，SRAM，唯一 ID，看门狗定时器 |
| 存储容量： | 64B |
| 时间格式： | HH:MM:SS:hh（12/24 小时） |
| 数据格式： | YY-MM-DD-dd |
| 接口： | SPI |
| 电源电压： | 1.8 V ~ 5.5 V |
| 电压 - 电源，电池： | 1.3 V ~ 5.5 V |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 14-TSSOP（0.173"，4.40mm 宽） |
| 供应商设备封装： | 14-TSSOP |
| 包装： | 带卷 (TR) |
MCP4902/4912/4922
DS22250A-page 30
2010 Microchip Technology Inc.
6.5
Bipolar Operation
Bipolar operation is achievable using the MCP4902/
4912/4922 family of devices by using an external
operational amplifier (op amp). This configuration is
desirable due to the wide variety and availability of op
amps. This allows a general purpose DAC, with its cost
and availability advantages, to meet almost any
desired output voltage range, power and noise
performance.
Example 6-3 illustrates a simple bipolar voltage source
configuration. R1 and R2 allow the gain to be selected,
while R3 and R4 shift the DAC’s output to a selected
offset. Note that R4 can be tied to VREF instead of VSS,
if a higher offset is desired. Also note that a pull-up to
VREF could be used instead of R4, if a higher offset is
desired.
EXAMPLE 6-3:
DIGITALLY-CONTROLLED BIPOLAR VOLTAGE SOURCE
6.5.1
DESIGN EXAMPLE: DESIGN A BIPOLAR
DAC USING EXAMPLE 6-3 WITH 12-BIT
MCP4922 OR MCP4921
An output step magnitude of 1 mV with an output range
of ±2.05V is desired for a particular application.
The following steps show the details:
Step 1: Calculate the range: +2.05V – (-2.05V) = 4.1V.
Step 2: Calculate the resolution needed:
4.1V/1 mV = 4100
Since 212 = 4096, 12-bit resolution is
desired.
Step 3:The amplifier gain (R2/R1), multiplied by VREF,
must be equal to the desired minimum output
to achieve bipolar operation. Since any gain
can be realized by choosing resistor values
(R1+R2), the VREF source needs to be deter-
mined first. If a VREF of 4.1V is used, solve for
the gain by setting the DAC to 0, knowing that
the output needs to be -2.05V. The equation
can be simplified to:
Step 4: Next, solve for R3 and R4 by setting the DAC to
4096, knowing that the output needs to be
+2.05V.
VREF
VDD
SPI
3
VOUT
R3
R4
2
R1
VIN+
0.1 F
VCC+
VCC–
VO
VIN+
VOUTR4
R3 R4
+
--------------------
=
VO
VIN+ 1
R2
R1
------
+
V
DD
R2
R1
------
–
=
G = Gain selection (1x or 2x)
Dn = Digital value of DAC (0-255) for MCP4901/MCP4902
VOUT
VREF G
Dn
2
N
------
=
= Digital value of DAC (0-1023) for MCP4911/MCP4912
= Digital value of DAC (0-4095) for MCP4921/MCP4922
N = DAC Bit Resolution
DAC
MCP4901
MCP4911
MCP4921
(a) Single Output DAC:
(b) Dual Output DAC:
MCP4902
MCP4912
MCP4922
R2
–
R1
---------
2.05
–
VREF
-------------
2.05
–
4.1
-------------
==
If R1 = 20 k and R2 = 10 k, the gain will be 0.5.
R2
R1
------
1
2
---
=
R4
R3 R4
+
-----------------------
2.05V 0.5VREF
+
1.5VREF
-----------------------------------------
2
3
---
==
If R4 = 20 k, then R3 = 10 k
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