参数资料
| 型号： | ADM1026EBZEVB |
| 厂商： | ON Semiconductor |
| 文件页数： | 21/55页 |
| 文件大小： | 0K |
| 描述： | BOARD EVAL FOR ADM1026 |
| 标准包装： | 1 |
| 类型： | 温度传感器 |
| 适用于相关产品： | ADM1026 |
| 所含物品： | 评估板 |
| 其它名称： | EVAL-ADM1026EB EVAL-ADM1026EB-ND |
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ADM1026
Pins 28 and 27 are measured both as analog inputs
A IN8 /A IN9 and as remote temperature input D2+/D2 ? ,
irrespective of which configuration is selected for these pins.
If Pins 28 and 27 are configured as A IN8 /A IN9 , the
measurements for these channels are stored in Registers 27h
and 29h, and the invalid temperature measurement is
discarded. On the other hand, if Pins 28 and 27 are configured
as D2+/D2 ? , the temperature measurement is stored in
Register 29h, and there is no valid result in Register 27h.
As mentioned previously, the ADC performs a conversion
every 711 m s on the analog and local temperature inputs and
every 2.13 ms on the remote temperature inputs. Each input
is measured 16 times and averaged to reduce noise.
The total monitoring cycle time for voltage and
temperature inputs is therefore nominally:
(18 16 0.711) ) (2 16 2.13) + 273 ms (eq. 11)
The ADC uses the internal 22.5 kHz clock, which has a
tolerance of ? 6%, so the worst-case monitoring cycle time
is 290 ms. The fan speed measurement uses a completely
separate monitoring loop, as described later.
? To amplify the 2.5 V range of the analog output up to
12 V, the gain of these circuits needs to be about 4.8.
? Take care when choosing the op amp to ensure that its
input common-mode range and output voltage swing
are suitable.
? The op amp may be powered from the +12 V rail alone
or from ? 12 V. If it is powered from +12 V, the input
common-mode range should include ground to
accommodate the minimum output voltage of the DAC,
and the output voltage should swing below 0.6 V to
ensure that the transistor can be turned fully off.
? If the op amp is powered from ? 12 V, precautions such
as a clamp diode to ground may be needed to prevent
the base-emitter junction of the output transistor being
reverse-biased in the unlikely event that the output of
the op amp should swing negative for any reason.
? In all these circuits, the output transistor must have an
I CMAX 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.
Input Safety
Scaling of the analog inputs is performed on-chip, so
external attenuators are typically not required. However,
because the power supply voltages appear directly at the
?
If the fan motor produces a large back EMF when
switched off, it may be necessary to add clamp diodes
to protect the output transistors in the event that the
output goes from full scale to zero very quickly.
pins, it is advisable to add small external resistors (that is,
500 W ) in series with the supply traces to the chip to prevent
damaging the traces or power supplies should an accidental
short such as a probe connect two power supplies together.
Because the resistors form part of the input attenuators,
they affect the accuracy of the analog measurement if their
value is too high. The worst such accident would be
connecting ? 12 V to +12 V where there is a total of 24 V
difference. With the series resistors, this would draw a
maximum current of approximately 24 mA.
Analog Output
DAC
1/4
LM324
R1
10k ?
12 V
Q1
2N2219A
The ADM1026 has a single analog output from an
unsigned 8-bit DAC that produces 0 V to 2.5 V
(independent of the reference voltage setting). The input
data for this DAC is contained in the DAC control register
Figure 35. Fan Drive Circuit with Op Amp and
Emitter-follower
12 V
(Address 04h). The DAC control register defaults to FFh
during a power-on reset, which produces maximum fan
speed. The analog output may be amplified and buffered
with external circuitry such as an op amp and a transistor to
provide fan speed control. During automatic fan speed
control, described later, the four MSBs of this register set the
DAC
1/4
LM324
R4
1k W
R3
1k W
Q1
BD136
2SA968
minimum fan speed.
Suitable fan drive circuits are shown in Figure 35 through
Figure 39. When using any of these circuits, note the
following:
? All of these circuits provide an output range from 0 V
to almost +12 V, apart from Figure 35, which loses the
base-emitter voltage drop of Q1 due to the
emitter-follower configuration.
R2
39k W
R1
10k ?
Figure 36. Fan Drive Circuit with Op Amp and PNP
Transistor
http://onsemi.com
21
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