參數(shù)資料
型號(hào): FDW2520C
廠(chǎng)商: Analog Devices, Inc.
英文描述: Thermoelectric Cooler Controller
中文描述: 熱電冷卻器控制器
文件頁(yè)數(shù): 20/24頁(yè)
文件大小: 416K
代理商: FDW2520C
REV. C
–20–
ADN8830
If the voltage at V
SY
drops below V
X
, Q1 is turned off and the
VLIM pin will be set to 1.5 V, effectively setting the maximum
voltage across the outputs to 0 V. The voltage divider for V
X
is
calculated from Equation 43.
Design Example 5
A maximum output current limit needs to be set at 1.5 A for a
TEC with a maximum voltage rating of 2.5 V. The ADN8830 is
powered from 5 V. The TEC resistance is estimated at 1.67
and
efficiency at 85%. Using Equation 43, the voltage drop across
R
S
will be 8.8 mV when 1.5 A is delivered to the TEC. The trip
voltage V
X
is set to 4.991 V with R3 = 178
and R4 = 100 k
as shown in Figure 21. To set the output voltage limit to 2.5 V,
the voltage at VLIMIT should be set to 0.875 V according to
Equation 17.
The C1 capacitor is added to smooth the voltage transitions at
VLIM. Once an overcurrent condition is detected, the output
voltage will turn down to 0 V within 30 ms.
For a more exact measurement of the output current, place a
sense resistor in series with the output load, as shown in Figure 23.
The AD626 instrumentation amplifier is set for a gain of 100
with a reference voltage of 2.47 V from VREF. The output of
the AD626 is equal to 100
×
R
S
×
I
L
and is fed to the AD8602,
which is set up as a window comparator. With V
X
greater than
VLO but less than VHI, VLIM will be pulled down to the volt-
age at VLIMIT. Should V
X
fall outside the voltage window,
VLIM will be pulled to 1.5 V as in Figure 21. The trip points
should be set according to
VHI
VLO
VREF
VREF
=
R I
R I
=
+
×
×
+
100
100
(44)
AVDD
Q1,Q2
FDG6303N
OR
EQUIVA-
LENT
8
TO
VREF
1nF
AVDD
TO
OUT B
R
S
10m
I
L
TO
TEC
VLIMIT
(0V TO 1.5V)
TO
VLIM
R2
1.47k
R1
3.48k
AVDD
200k
300k
300k
200k
V
X
V
LO
AD8602
AD626
AVDD
V
HI
Figure 23. High Accuracy Output Current Limit
The upper and lower trip point voltages can be set independently,
allowing different maximum output current limits depending on
the direction of the current. The resistor divider for VHI and
VLO is tapped to VREF to maintain window accuracy with any
changes in VREF. Using the values from Figure 23 with a 5 V
supply, the output current will not exceed 1.5 A in either direction.
Adding the current sensing resistor will slightly reduce efficiency.
The power dissipated by this resistor is D
×
ITEC2
×
R
S
if the
TEC is heating, or (1
D)
×
ITEC2
×
R
S
if the TEC is cooling.
Include this when calculating efficiency as described in the
Calculating Power Dissipation and Efficiency section.
25mV/ C
OUT
OA
ADT70
1k
OUT
IA
–IN
OA
5.11k
AGND
4.99k
RGA
RGB
INST
AMP
–IN
IA
+IN
IA
+IN
OA
R3
1k
R3
82.5
I
OUTB
I
OUTA
RTD
1k
R3
82.5
GND
SENSE
5V
NOTE: ADDITIONAL PINS OMITTED FOR CLARITY
TO THERM_IN
= 1V @ 25 C
Figure 22. Using an RTD for Temperature Feedback to the ADN8830
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