ADM1028ARQ ON Semiconductor, ADM1028ARQ Datasheet - Page 9

• Manufacturer Part Number: ADM1028ARQ
• Description: IC SENSOR TEMP/FAN CTRL 16QSOP
• Manufacturer: ON Semiconductor

Specifications of ADM1028ARQ

• Rohs Status: RoHS non-compliant
• Function: Fan Control, Temp Monitor
• Topology: ADC, Register Bank
• Sensor Type: External & Internal
• Sensing Temperature: 0°C ~ 100°C, External Sensor
• Output Type: SMBus™
• Output Alarm: No
• Output Fan: Yes
• Voltage - Supply: 3 V ~ 5.5 V
• Operating Temperature: 0°C ~ 100°C
• Mounting Type: Surface Mount
• Package / Case: 16-QSOP

7. For really long distances (up to 100 feet) use shielded twisted-
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 W 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
2. To amplify the 2.5 V range of the analog output up to
3. Care must be taken when choosing the op amp to ensure
4. The op amp may be powered from the +V rail alone. If it is
5. In all these circuits, the output transistor must have an I
6. If the fan motor produces a large back e.m.f. when switched
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.
REV. B
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.
to almost +V
+V
that its input common-mode range and output voltage swing
are suitable.
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.
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.
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.
FAN
GND
GND
D+
D–
, the gain of these circuits needs to be set as shown.
Figure 4. Arrangement of Signal Tracks
FAN
.
10MIL
10MIL
10MIL
10MIL
10MIL
10MIL
10MIL
CMAX
–9–
FAN_SPD
Figure 5b. 12 V Fan Circuit with Op Amp and PNP
Transistor
FAN_SPD
Figure 5c. 12 V Fan Circuit with Op Amp and
P-Channel MOSFET
Figure 5d. Discrete 12 V Fan Drive Circuit with
P-Channel MOSFET, Single Supply
Figure 5e. Discrete 12 V Fan Drive Circuit with
Bipolar Output Single Supply
FAN_SPD
FAN_SPD
Figure 5a. 5 V Fan Circuit with Op Amp
FAN_SPD
5k
R6
5k
100k
R5
MBT3904
R5
Q1/Q2
DUAL
R1
10k
100k
R1
10k
R1
10k
MBT3904
AD8519
+
FAN_OFF
R3
Q1/Q2
DUAL
AD8519
AD8541
+
+
R4
100k
39k
100
R2
R4
100k
R3
15k
1k
R2
39k
R4
3.9k
1k
R3
R2
3.3V
1k
Q3
BC556
2N3906
R2
R1
100k
R3
1k
3.9k
5V
R4
1k
Q1
NDT452 P
12V
R2
R1
ADM1028
12V
12V
Q1
NDT452 P
Q2
MMFT305 5V
5V
FAN
Q3
NDT452 P
Q1
BD136
2SA968
12V
Q4
BD132
TIP32A