EVAL-ADM1026EB ON Semiconductor, EVAL-ADM1026EB Datasheet - Page 22

• Manufacturer Part Number: EVAL-ADM1026EB
• Description: BOARD EVAL FOR ADM1026
• Manufacturer: ON Semiconductor
• Type: Temperature Sensorr

Specifications of EVAL-ADM1026EB

• Contents: Evaluation Board
• For Use With/related Products: ADM1026
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

PWM Output
modulation (PWM). The PWM output (Pin 18) produces a
pulsed output with a frequency of approximately 75 Hz and
a duty cycle defined by the contents of the PWM control
register (Address 05h). During automatic fan speed control,
described below, the four MSBs of this register set the
minimum fan speed.
Figure 38. Discrete Fan Drive Circuit with P−Channel
Figure 39. Discrete Fan Drive Circuit with P−Channel
Fan speed may also be controlled using pulse width
DAC
Figure 37. Fan Drive Circuit with Op Amp and
DAC
DAC
R2
100kW
MBT3904
Q1/Q2
DUAL
MOSFET, Single Supply
MOSFET, Dual Supply
MBT3904
P−Channel MOSFET
Q1/Q2
DUAL
–12 V
R1
10kΩ
1/4
LM324
R1
4.7kΩ
R2
100kW
R2
100kW
R2
39kW
R3
100kW
R4
10kΩ
R3
39kΩ
R3
39kΩ
R4
10kΩ
12 V
IRF9620
Q1
Q3
IRF9620
12 V
+12 V
Q3
IRF9620
http://onsemi.com
22
buffered to drive the fans. The PWM output is intended to
be used with an NMOS driver, but may be inverted by setting
Bit 1 of Test Register 1 (Address 14h) if using PMOS
drivers. Figure 40 shows how a fan may be driven under
PWM control using an N−channel MOSFET.
Automatic Fan Speed Control
speed according to temperature without intervention from
the host processor. Monitoring must be enabled by setting
Bit 0 of Configuration Register 1 (Address 00h), to enable
automatic fan speed control. Automatic fan speed control
can be applied to the DAC output, the PWM output, or both,
by setting Bit 5 and/or Bit 6 of Configuration Register 1.
minimum temperature values for the three temperature
channels (on−chip sensor and two remote diodes). This is the
temperature at which a fan starts to operate when the
temperature sensed by the controlling sensor exceeds T
T
T
to the T
for automatic fan speed control, T
should be set to 127°C (01111111).
NO TAG and Figure 43) the four MSBs of the DAC control
register (Address 04h) and PWM control register (Address
05h) set the minimum values for the DAC and PWM outputs.
Note that, if both DAC control and PWM control are enabled
(Bits 5 and 6 of Configuration Register 1 = 1), the four MSBs
of the DAC control register (Address 04h) define the
minimum fan speed values for both the DAC and PWM
outputs. The value in the PWM control register (Address 05h)
has no effect.
where D is the decimal equivalent of Bits 7 to 4 of the
register.
MIN
MIN
The open drain PWM output must be amplified and
The ADM1026 offers a simple method of controlling fan
The T
In automatic fan speed control mode, (as shown Figure
Minimum DAC Code DAC
Minimum PWM Duty Cycle PWMMIN = 6.67 × D
is set by writing a twos complement temperature value
can be the same or different for all three channels.
Figure 40. PWM Fan Drive Circuit Using an
DAC Output Voltage + 2.5
MIN
PWM
MIN
registers. If any sensor channel is not required
registers (Addresses 10h to 12h) contain
3.3 V
10kΩ TYP
N−Channel MOSFET
MIN
+V
NDT3055L
Q1
= 16 × D
MIN
Code
256
5.0 V OR 12 V
FAN
for that channel
(eq. 12)
MIN
.