tcn75a Microchip Technology Inc., tcn75a Datasheet - Page 21

• Manufacturer Part Number: tcn75a
• Description: 2-wire Serial Temperature Sensor
• Manufacturer: Microchip Technology Inc.

5.3.4.1
The Shutdown mode disables all power-consuming
activities (including temperature sampling operations)
while leaving the serial interface active. The device
consumes 2 μA (max.) in this mode. It remains in this
mode until the Configuration register is updated to
enable continuous conversion or until power is
recycled.
In Shutdown mode, the CONFIG, T
registers can be read or written to; however, the serial
bus activity will increase the shutdown current.
5.3.4.2
The TCN75A can also be used in a One-shot mode that
can be selected using bit 7 of the CONFIG register. The
One-shot mode performs a single temperature
measurement and returns to Shutdown mode. This
mode is especially useful for low-power applications
where temperature is measured upon command from a
controller. For example, a 9-bit T
consumes 200 μA (typ.) for 30 ms and 0.1 μA (typ.)
during shutdown.
To access this feature, the device needs to initially be
in Shutdown mode. This is done by sending a byte to
the CONFIG register with bit 0 set <1> and bit 7 cleared
<0>. Once the device is in Shutdown mode, the
CONFIG register needs to be written to again, with bit
0 and bit 7 set <1>. This begins the single conversion
cycle of t
conversion is completed, T
CONFIG becomes cleared <0> by the TCN75A.
TABLE 5-6:
© 2006 Microchip Technology Inc.
Continuous Conversion
Shutdown
Continuous Conversion
(One-shot is ignored)
One-shot (Note 1)
Note 1:
Operational Mode
CONV
The shutdown command <01> needs to
be programmed before sending a one-
shot command <11>.
Shutdown Mode
One-Shot Mode
, 30ms for 9-bit data. Once the
SHUTDOWN AND ONE-SHOT
MODE DESCRIPTION
A
One-Shot
is updated and bit 7 of
(Bit 7)
A
0
0
1
1
A
in One-shot mode
, T
SET
Shutdown
and T
(Bit 0)
0
1
0
1
HYST
5.3.4.3
The ALERT output can be configured as either a
comparator output or as Interrupt Output mode using
bit 1 of CONFIG. The polarity can also be specified as
an active-high or active-low using bit 2 of CONFIG.
The following sections describe each output mode,
while Figure 5-6 gives a graphical description.
5.3.4.4
In Comparator mode, the ALERT output is asserted
when T
until T
useful for thermostat-type applications, such as turning
on a cooling fan or triggering a system shutdown when
the temperature exceeds a safe operating range.
In Comparator mode, if the device enters the Shutdown
mode with asserted ALERT output, the output remains
active during shutdown. The device must be operating
in continuous conversion, with T
ALERT output to be deasserted.
5.3.4.5
In Interrupt mode, the ALERT output is asserted when T
is greater than T
when the user performs a read from any register. This
mode is designed for interrupt-driven, microcontroller-
based systems. The microcontroller receiving the inter-
rupt will have to acknowledge the interrupt by reading
any register from the TCN75A. This will clear the interrupt
and the ALERT pin will become deasserted. When T
drifts below T
and the controller needs to read a register to deassert the
ALERT output. Shutting down the device will also reset,
or deassert, the ALERT output.
FIGURE 5-6:
T
ALERT
T
T
ALERT
Comparator mode
Interrupt mode
Register
Read
SET
A
HYST
Active-low
Active-low
* See Section 5.3.4.5 “Interrupt Mode”
A
A
is lower than T
is greater than T
HYST
ALERT Output Configuration
Comparator Mode
Interrupt Mode
SET
, the TCN75A outputs another interrupt
. However, the output is deasserted
Alert Output.
HYST
*
SET
. The Comparator mode is
. The pin remains active
A
TCN75A
below T
DS21935C-page 21
HYST
, for the
A
A