MGSF1N02E View Datasheet(PDF) - Microchip Technology
Part Name
Description
Manufacturer
MGSF1N02E Datasheet PDF : 28 Pages
| |||
TC642
3.0 DETAILED DESCRIPTION
3.1 PWM
The PWM circuit consists of a ramp generator and
threshold detector. The frequency of the PWM is deter-
mined by the value of the capacitor connected to the CF
input. A frequency of 30 Hz is recommended
(CF = 1 µF). The PWM is also the time base for the
Start-up Timer (see Section 3.4, “Start-Up Timer”). The
PWM voltage control range is 1.25V to 2.65V (typical)
for 0% to 100% output duty cycle.
3.2 FAULT Output
The TC642 detects faults in two ways.
First, pulses appearing at SENSE due to the PWM
turning on are blanked, with the remaining pulses
filtered by a missing pulse detector. If consecutive
pulses are not detected for 32 PWM cycles (≅1 Sec if
CF = 1 µF), the Diagnostic Timer is activated, and VOUT
is driven high continuously for three PWM cycles
(≅100 msec if CF = 1 µF). If a pulse is not detected
within this window, the Start-up Timer is triggered (see
Section 3.4). This should clear a transient fault condi-
tion. If the missing pulse detector times out again, the
PWM is stopped and FAULT goes low. When FAULT is
activated due to this condition, the device is latched in
shutdown mode and will remain off indefinitely.
Note:
At this point, action must be taken to restart
the fan by momentarily pulling VMIN below
VSHDN, or cycling system power. In either
case, the fan cannot remain disabled due
to a fault condition, as severe system dam-
age could result. If the fan cannot be
restarted, the system should be shut down.
The TC642 may be configured to continuously attempt
fan restarts, if so desired.
Continuous restart mode is enabled by connecting the
FAULT output to VMIN through a 0.01 µF capacitor, as
shown in Figure 3-1. When connected in this manner,
the TC642 automatically attempts to restart the fan
every time a fault condition occurs. When the FAULT
output is driven low, the VMIN input is momentarily
pulled below VSHDN, initiating a reset and clearing the
fault condition. Normal fan start-up is then attempted as
previously described. The FAULT output may be
connected to external logic (or the interrupt input of a
microcontroller) to shut the TC642 down if multiple fault
pulses are detected at approximately one second
intervals. Diode D1, capacitor C1 and resistors R5 and
R6 are provided to ensure fan restarts are the result of
a fan fault and not an over-temperature fault. A CMOS
logic OR gate may be substituted for these
components, if available.
From
System
Shutdown
Controller
C1
0.01µF
From
Temp
Sensor
+5V
1
VIN
R1
Q2
(Optional)
R3
3 VMIN
CB
0.01µF
2
R4
CF
CF
1µF
+5V
8
VDD
VDD
R5
10kΩ
D1
R6
1kΩ
6
FAULT
TC642
VOUT 7
5
SENSE
GND
4
+12V
TC642
RESET
1
0
Fault
Detected
Fan
Q1
RBASE
CSENSE
RSENSE
*The parallel combination of R3 and R4 must be >10 kΩ.
FIGURE 3-1:
Fan Fault Output Circuit.
2002 Microchip Technology Inc.
DS21444C-page 5
Share Link: 