参数资料
型号: ADT7468ARQZ-REEL
厂商: ON Semiconductor
文件页数: 29/81页
文件大小: 0K
描述: IC REMOTE THERMAL CTRLR 24QSOP
产品变化通告: MFG CHG Notification ADI to ON Semi
Product Obsolescence 11/Feb/2009
标准包装: 2,500
系列: dBCool®
功能: 风扇控制,温度监控器
传感器类型: 内部和外部
感应温度: -40°C ~ 120°C,外部传感器
精确度: ±2°C(最小值)
拓扑: ADC,比较器,风扇速度计数器,多路复用器,寄存器库
输出类型: SMBus?
输出警报:
输出风扇:
电源电压: 3 V ~ 5.5 V
工作温度: -40°C ~ 120°C
安装类型: 表面贴装
封装/外壳: 24-SSOP(0.154",3.90mm 宽)
供应商设备封装: 24-QSOP
包装: 带卷 (TR)
ADT7468
Driving Two Fans from PWM3
The ADT7468 has four TACH inputs available for fan speed
measurement, but only three PWM drive outputs. If a fourth
fan is being used in the system, it should be driven from the
PWM3 output in parallel with the third fan. Figure 37 shows
how to drive two fans in parallel using low cost NPN
transistors. Figure 38 shows the equivalent circuit using a
MOSFET.
Because the MOSFET can handle up to 3.5 A, a second fan can
be connected directly in parallel with the first. Care should be
taken in designing drive circuits with transistors and FETs to
ensure that the PWM pins are not required to source current
and that they sink less than the 5 mA maximum current
specified in the data sheet.
Driving up to Three Fans from PWM3
TACH measurements for fans are synchronized to particular
PWM channels; for example, TACH1 is synchronized to
PWM1. TACH3 and TACH4 are both synchronized to PWM3,
and therefore PWM3 can drive two fans. Alternatively, PWM3
can be programmed to synchronize TACH2, TACH3, and
TACH4 to the PWM3 output. This allows PWM3 to drive two
or three fans. In this case, the drive circuitry is as shown in
Figure 37 and Figure 38. The SYNC bit in Register 0x62 enables
this function.
Synchronization is not required in high frequency mode when
used with 4-wire fans.
<4> (SYNC) Enhance Acoustics Register 1 (Reg. 0x62)
SYNC = 1, synchronizes TACH2, TACH3, and TACH4 to
PWM3.
12V
ADT7468
PWM3
3.3V
1k ?
2.2k ?
3.3V
TACH3
Q1
MMBT3904
10 ?
Q2
TACH4
MMBT2222
10 ?
Q3
MMBT2222
Figure 37. Interfacing Two Fans in Parallel to the PWM3 Output Using Low Cost NPN Transistors
3.3V
10k ?
TYPICAL
TACH4
ADT7468
3.3V
10k ?
+V
+V
TYPICAL
TACH3
3.3V
TACH
5V OR
12V FAN
1N4148
TACH
5V OR
12V FAN
10k ?
TYPICAL
PWM3
Q1
NDT3055L
Figure 38. Interfacing Two Fans in Parallel to the PWM3 Output Using a Single N-Channel MOSFET
Rev. 3 | Page 29 of 81 | www.onsemi.com
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