datasheetbank_Logo
Integrated circuits, Transistor, Semiconductors Search and Datasheet PDF Download Site

ADM1028 View Datasheet(PDF) - Analog Devices

Part Name
Description
View to exact match
ADM1028 Datasheet PDF : 16 Pages
1 2 3 4 5 6 7 8 9 10 Next Last
7. For really long distances (up to 100 feet) use shielded twisted-
pair such as Belden #8451 microphone cable. Connect the
twisted pair to D+ and D– and the shield to GND close to
the ADM1028. Leave the remote end of the shield uncon-
nected to avoid ground loops.
GND
D+
D
GND
10MIL
10MIL
10MIL
10MIL
10MIL
10MIL
10MIL
Figure 4. Arrangement of Signal Tracks
Because the measurement technique uses switched current
sources, excessive cable and/or filter capacitance can affect the
measurement. When using long cables, the filter capacitor C1
may be reduced or removed. In any case, the total shunt capaci-
tance should not exceed 1000 pF.
Cable resistance can also introduce errors. 1 series resistance
introduces about 0.5°C error.
ANALOG OUTPUT
The ADM1028 has a single analog output (FAN_SPD) from an
unsigned 8-bit DAC which produces 0 V–2.5 V. The analog
output register defaults to 00 during power-on reset, which pro-
duces minimum fan speed. The analog output may be amplified
and buffered with external circuitry such as an op amp and tran-
sistor to provide fan speed control.
Suitable fan drive circuits are given in Figures 5a to 5e. When
using any of these circuits, the following points should be noted:
1. All of these circuits will provide an output range from zero
to almost +VFAN.
2. To amplify the 2.5 V range of the analog output up to
+VFAN, the gain of these circuits needs to be set as shown.
3. Care must be taken when choosing the op amp to ensure
that its input common-mode range and output voltage swing
are suitable.
4. The op amp may be powered from the +V rail alone. If it is
powered from +V then the input common-mode range
should include ground to accommodate the minimum out-
put voltage of the DAC, and the output voltage should
swing below 0.6 V to ensure that the transistor can be
turned fully off.
5. In all these circuits, the output transistor must have an ICMAX
greater than the maximum fan current, and be capable of
dissipating power due to the voltage dropped across it when
the fan is not operating at full-speed.
6. If the fan motor produces a large back e.m.f. when switched
off, it may be necessary to add clamp diodes to protect the
output transistors in the event that the output very quickly
goes from full-scale to zero.
Figure 5c shows how the FAN_OFF signal may be used (with
any of the control circuits) to gate the fan on and off indepen-
dent of the value on the FAN_SPD/NTEST_IN pin.
ADM1028
FAN_SPD
AD8541
+
R2
15k
R1
10k
5V
Q1
NDT452 P
5V
FAN
Figure 5a. 5 V Fan Circuit with Op Amp
FAN_SPD
AD8519
+
R3
1k
R2
39k
R4 12V
1k
Q1
BD136
2SA968
R1
10k
Figure 5b. 12 V Fan Circuit with Op Amp and PNP
Transistor
FAN_SPD
R3 12V
100k
AD8519
+
R2
39k
Q1
NDT452 P
R1
10k
FAN_OFF
3.3V
R4
1k
Q2
MMFT305 5V
Figure 5c. 12 V Fan Circuit with Op Amp and
P-Channel MOSFET
12V
R3
100k
R4
100k
FAN_SPD
R5
5k
Q1/Q2
MBT3904
DUAL
R2
3.9k
R1
1k
Q3
NDT452 P
Figure 5d. Discrete 12 V Fan Drive Circuit with
P-Channel MOSFET, Single Supply
12V
FAN_SPD
R6
5k
R5
100k
Q1/Q2
MBT3904
DUAL
R4
100k
Q3
BC556
2N3906
R2
3.9k
R3
100
R1
1k
Q4
BD132
TIP32A
Figure 5e. Discrete 12 V Fan Drive Circuit with
Bipolar Output Single Supply
REV. A
–9–
 

Share Link: 

datasheetbank.com [ Privacy Policy ] [ Request Datasheet ] [ Contact Us ]