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参数资料
| 型号： | ADN8830ACPZ-REEL |
| 厂商： | Analog Devices Inc |
| 文件页数： | 9/22页 |
| 文件大小： | 0K |
| 描述： | IC THERMO COOLER CNTRLR 32-LFCSP |
| 标准包装： | 1 |
| 应用： | 热电冷却器 |
| 电流 - 电源： | 8mA |
| 电源电压： | 3.3 V ~ 5 V |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 32-VFQFN 裸露焊盘，CSP |
| 供应商设备封装： | 32-LFCSP-VQ（5x5） |
| 包装： | 剪切带 (CT) |
| 其它名称： | ADN8830ACPZ-REELCT |
ADN8830
Although the thermistor has a nonlinear relationship to tem-
perature, near optimal linearity over a specified temperature
range can be achieved with the proper value of R X . First, the
resistance of the thermistor must be known, where
The setpoint voltage can be driven from a DAC or another
voltage source, as shown in Figure 4. The reference voltage
for the DAC should be connected to VREF (Pin 7) on the
ADN8830 to ensure best accuracy from device to device.
R THERM = R T 1 @ T = T LOW
= R T 2 @ T = T MID
= R T 3 @ T = T HIGH
(2)
For a fixed target temperature, a voltage divider network can be
used as shown in Figure 5. R1 is set equal to R X , and R2 is
equal to the value of R THERM at the target temperature.
T LOW and T HIGH are the endpoints of the temperature range and
T MID is the average. These resistances can be found in most
3.3V
7
3.3V
8
thermistor data sheets. In some cases, only the coefficients
corresponding to the Steinhart-Hart equation are given. The
1–4
AD7390
6
4
[
= a + b 1 n ( R ) + c 1 n ( R )
]
Steinhart-Hart equation is
1
T
3
(3)
C
5
8
7
ADN8830
where T is the absolute temperature of the thermistor in Kelvin
(K = ° C + 273.15), and R is the resistance of the thermistor at
that temperature. Based on the coefficients a , b , and c , R THERM
can be calculated for a given T , albeit somewhat tediously, by
solving the cubic roots of this equation
30
Figure 4. Using a DAC to Control the Temperature
Setpoint
= exp ? ? –
? ?
+ ?
χ ? χ 2 ψ 3 ? 2 ?
? ?
?
+ ? – – ?
? χ ? χ 2 ψ 3 ? 2 ? ? (4)
2 4 27 ? ? ? ?
?
? ?
? ?
R THERM
?
? ?
? ?
? ?
?
2 ? 4 27 ?
+
1
1 ? 3
?
? 1 ? 3 ?
?
?
+
1 ?
?
R1
7
3.3V
8
where
4
ADN8830
X =
a –
c
1
T and ψ =
b
c
R2
30
R X = T 1 T 2
R X is then found as
R R + R T 2 R T 3 – 2 R T 1 R T 3
R T 1 + R T 3 – 2 R T 2
(5)
Figure 5. Using a Voltage Divider to Set a Fixed
Temperature Setpoint
Design Example 1
V X = VREF
+ R
V SET = m ( T – T MID ) + V XMID
m =
T HIGH – T LOW
THERMIN Voltage Range = m × ( T MAX MIN )
For the best accuracy as well as the widest selection range for
resistances, R X should be 0.1% tolerance. Naturally, the smaller
the temperature range required for control, the more linear
the voltage divider will be with respect to temperature. The
voltage at THERMIN is
R THERM
(6)
R THERM X
where VREF has a typical value of 2.47 V.
The ADN8830 control loop will adjust the temperature of the
TEC until V X equals the voltage at TEMPSET (Pin 4), which
we define as V SET . Target temperature can be set by
(7)
where T equals the target temperature, and
V X , HIGH – V X , LOW
(8)
V X for high, mid, and low are found by using Equation 6 and
substituting R T3 , R T2 , and R T1 , respectively, for R THERM . The
variable m is the change in V X with respect to temperature and
is expressed in V/ ° C.
REV. D
–9 –
A laser module requires a constant temperature of 25 ° C. From
the manufacturer’s data sheet, we find the thermistor in the laser
module has a value of 10 k Ω at 25 ° C. Because the laser is not
required to operate at a range of temperatures, the value of R X
can be set to 10 k Ω . TEMPSET can be set by a simple resistor
divider as shown in Figure 5, with R1 and R2 both equal to 10 k Ω .
Design Example 2
A laser module requires a continuous temperature control from
5 ° C to 45 ° C. The manufacturer’s data sheet shows the thermistor
has a value of 10 k Ω at 25 ° C, 25.4 k Ω at 5 ° C, and 4.37 k Ω at
45 ° C. Using Equation 5, R X is calculated to be 7.68 k Ω to yield
the most linear temperature-to-voltage conversion. A DAC
will be used to set the TEMPSET voltage.
DAC Resolution for TEMPSET
The temperature setpoint voltage to THERMIN can be set from
a DAC. The DAC must have a sufficient number of bits to achieve
adequate temperature resolution from the system. The voltage
range for THERMIN is found by multiplying the variable m
from Equation 8 by the temperature range.
– T (9)
From Design Example 2, 40 ° C of the control temperature range
is achieved with a voltage range of only 1 V.
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