Philips Semiconductors Product data sheet
NE1619HECETA4 Temperature and voltage monitor
2004 Oct 05
12
FUNCTIONAL DESCRIPTION
SMBus serial interface
The NE1619 can be connected to a compatible 2-wire serial
interface SMBus as a slave device under the control of a master
device or controller, using two device terminals SCL and SDA. The
controller will provide a clock signal to the device SCL pin and
write/read data to/from the device through the SDA pin.
Data of 8-bit digital byte or word are used for communication
between the controller and the device.
Notice that external pull-up resistors, about 10 kΩ, are needed for
the two terminals SCL and SDA.
Slave address
The NE1619 slave address on the SMBus is defined by the
hardware connection applied to the device pin 16. At power-up this
pin is automatically reset to its address sensing function A0. This
logic input will set up the value of the LSB bit of the 7-bit address.
Because A0 is a two-level digital input and the other 6 bits of the
address are predefined to 010110, only two slave addresses can be
used as listed below for the device:
Table 7.
A0 connection (Pin 16) Slave address
GND 0101100
V
DD
0101101
Because the logic is sampled and latched into the device storage
only at power-up, the device pin 16 can be programmed for different
functions while power is on without effecting the address definition.
Registers
The NE1619 contains a number of registers, as listed in Table 1, in
order to store data of the device setup and operation results. The
table indicates the command value and read/write capability of each
register for SMBus communication and also the power-up default
values for some registers. It includes:
– Configuration register to provide control and configuration as well
as initialization the NE1619,
– Status registers to provide the flags resulting from limit
comparisons,
– Reading registers to store results of measurements,
– Limit registers to store programmable limit data,
– ID and test registers.
Data are stored in registers by 8-bit digital byte, either in 2’s
complement format for temperature-related data or in straight format
for others. Writing and reading registers will be done on the SMBus
by a controller using the SMBus protocols that will be described
more in the last section of this functional description. Notice that
attempting to write to a “Read only” register will produce an invalid
result.
Power-on reset
When the power is applied to the NE1619, also called hardware
reset, the registers are reset to their default value, if defined, as
shown in Table 1. The content of registers which have indeterminate
default value such as reading registers will be unknown. The
on-board A-to-D converter is disabled and the monitoring function is
not started. The device enters standby mode and draws a supply
current less than 100 µA.
Because all limit registers are reset to zero, writing limits into the
limits registers should usually be the first action to be performed
after power-on reset.
Initialization
Initialization or software reset of the NE1619 can be initiated by
setting bit 7 of the configuration register. This bit automatically clears
itself after being set. The initialization performs a similar reset function
to power-on reset, except that the reading and limit registers are
not reset.
Starting conversion
The NE1619 monitoring function is started by setting (to 1) the
START bit (bit 0) of the configuration register. The device then
performs a loop of monitoring about every second. In monitoring
function, the device cycles sequentially through all measurements of
temperatures and voltages and also performs the comparisons
between readings and limits accordingly. The inputs are sampled in
this order: Remote diode temperature, Local temperature, V
DD
V
IN
,
12V
IN
, 5V
IN
. 3.3V
IN,
2.5V
IN
and V
CCPVIN
.
Measured values are stored in reading registers and results of limit
comparison are reflected by the state of the flag bits in the status
registers. Reading and status data can be read at any time. Limit
values should be written into limit registers before starting
conversion to avoid false conditions of the status.
Resetting (to 0) the START bit (bit 0) of the configuration register will
stop the monitoring function and put the device into its standby
mode thereby reducing power consumption.
Temperature measurement
The NE1619 contains an on-chip temperature sensor to measure
the local or internal temperature and provides input pins (D– and
D+) to measure the remote or external temperature with the use of a
remote diode-type sensor. The remote sensor should be connected
to the D– and D+ pins properly.
The method of temperature measurement is based on the change of
the diode VBE at two different operating current levels given by:
∆VBE = (KT/q)*LN(N)
where:
K: Boltzmann’s constant
T: absolute temperature in °K
q: charge on the electron
N: ratio of the two currents
LN: natural logarithm
The NE1619 provides two current sources of about 10 µA and
100 µA during the measurement of the remote diode VBE and the
sensed voltage between two pins D– and D+ is limited within 0.25 V
and 0.95 V.
The external diode should be selected to meet this current and
voltage requirements. The diode-connected PNP transistor provided
on the Pentium series microprocessor is typically used, or the
discrete diode-connected transistor 2N3904 is recommended.
For temperature measurement, local or remote, the ∆VBE is
converted into digital data by the on-chip sigma-delta A-to-D
converter. The result is stored in the temperature reading register
and is also compared with the limits stored in the temperature limit
registers in order to set the temperature flag bits in the status
register as described in Table 3.
