AMC6821-Q1 Datasheet, PDF (40/54 Pages) Texas Instruments – INTELLIGENT TEMPERATURE MONITOR AND PWM FAN CONTROLLER

AMC6821-Q1
SBAS475 – JUNE 2009 ...................................................................................................................................................................................................... www.ti.com
Status Register 2 (Address 0x03, Value After Power-On or Reset = 0x00)
BIT
NAME
R/W DEFAULT
DESCRIPTION
7
THERM-IN
R
Status of the THERM pin as an input. When this input is pulled low, THERM-IN = 1, and
0
the fan is driven at full speed. This bit is cleared when reading this register and be
written to '1' if the pin persists "pulled-low".
6
L-THERM
R
Local temperature over the local THERM limit flag. L-THERM = 1 when the local
temperature is greater than the value of the Local-THERM-Limit register. Otherwise,
L-THERM = 0. When L-THERM is set to 1, the THERM pin goes low. It also generates a
0
THERM interrupt through the SMBALERT pin, if enabled (THERMOVIE = 1). This bit is
cleared on a read of Status Register 1. Once cleared, this bit is not reasserted until the
temperature falls 5°C below the THERM limit, even if the THERM condition persists.
Refer to the THERM Pin and External Hardware Control section.
5
LPSV
R
Active control temperature below the PSV (passive cooling) temperature flag. This bit is
set to '1' when the active control temperature is equal to or below the PSV temperature.
0
Otherwise, this bit is cleared ('0'). LPSV = 1 generates a PSV interrupt on SMBALERT, if
enabled (PSVIE = 1). This bit is cleared when reading this register. If the active control
temperature remains equal to or below the PSV temperature, this bit reasserts on the
next monitoring cycle.
4
LTC
R
Local temperature over the local critical temperature flag. This bit is set ('1') when the
local temperature is equal to or above the local critical temperature. LTC = 0 if the local
0
critical temperature is below this value. LTC = 1 asserts the OVR pin low and generates
an LTC interrupt (non-maskable) though the SMBALERT pin. This bit is cleared when
reading this register. If the over-critical limit condition persists, this bit reasserts on the
next monitoring cycle.
3
RTC
R
Remote temperature over the remote critical temperature flag. This bit is set to '1' when
the remote temperature is equal to or above the remote critical temperature. RTC = 0 if
0
the remote critical temperature is below this value. RTC = 1 asserts the OVR pin low and
generates an RTC interrupt (non-maskable) though the SMBALERT pin. This bit is
cleared when reading this register. If the over-critical limit condition persists, this bit
reasserts on next monitoring cycle.
2
Reserved
R
0
Reserved. Reading returns '0'.
1
Reserved
R
0
Reserved. Reading returns '0'.
0
Reserved
R
0
Reserved. Reading returns '0'.
FAN CONTROLLER REGISTERS
DCY (Duty Cycle) Register (Address 0x22, Value After Power-On or Reset = 0x55)
BIT
7 (MSB)
6
5
4
3
2
1
0
NAME
DCY7 (MSB)
DCY6
DCY5
DCY4
DCY3
DCY2
DCY1
DCY0
DEFAULT
0
1
0
1
0
1
0
1
DESCRIPTION
DCY CODE
DUTY CYCLE
0x00
0%
0x01
0.392%
... ...
... ...
0x40
25%
... ...
... ...
0x80
50%
... ...
... ...
0xFF
100%
The DCY register stores the value of the PWM duty cycle, 0x00 corresponds to 0%, and 0xFF to 100%. 1LSB
corresponds to 0.392%. Power-on default = 0x55, 33.2%.
In a read operation, with the two following exceptions, the returned data are the actual duty cycle (DCY) value
driving the PWM-Out pin:
1. When TACH-MODE = 0 and the system is in software-RPM control mode, if the calculated duty cycle is less
than 30%, the returned value is the calculated value, not the actual PWM-OUT pin duty cycle which is forced
to 30%.
2. When TACH-MODE = 0 and the system is in software DCY-control mode or Auto Temperature-Fan mode, if
the calculated duty cycle is less than 7%, the returned value is the calculated value, not the actual
PWM-OUT pin duty cycle which is forced to 0%.
40
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