X40030_13 Datasheet, PDF (8/23 Pages) Intersil Corporation – Triple Voltage Monitor with Integrated CPU Supervisor

WDO
SCL
V_TRIPX
X40030, X40031, X40034, X40035
(X = 1, 2, 3)
V_CC/V2MON/V3MON
V_P
0
70
7
0
7
SDA
A0h
00h
t_WC
FIGURE 3. V_TRIPX SET/RESET CONDITIONS
Watchdog Timer
The Watchdog Timer circuit monitors the microprocessor
activity by monitoring the SDA and SCL pins. A standard
read or write sequence to any slave address byte restarts
the watchdog timer and prevents the WDO signal from going
active. A minimum sequence to reset the watchdog timer
requires four microprocessor instructions namely, a Start,
Clock Low, Clock High and Stop. The state of two nonvolatile
control bits in the Status Register determine the watchdog
timer period. The microprocessor can change these
watchdog bits by writing to the X40030, X40031, X40034,
X40035 control register (also refer to page 21).
SCL
0.6µs
1.3µs
SDA
START
WDT RESET STOP
FIGURE 4. WATCHDOG RESTART
V1, V2 and V3 Threshold Program
Procedure (Optional)
The X40030 is shipped with standard V1, V2 and V3
threshold (V_TRIP1, V_TRIP2, V_TRIP3) voltages. These values
will not change over normal operating and storage
conditions. However, in applications where the standard
thresholds are not exactly right, or if higher precision is
needed in the threshold value, the X40030, X40031, X40034,
X40035 trip points may be adjusted. The procedure is
described in the following and uses the application of a high
voltage control signal.
Setting a V_TRIPx Voltage (x = 1, 2, 3)
There are two procedures used to set the threshold voltages
(V_TRIPx), depending upon if the threshold voltage to be stored
is higher or lower than the present value. For example, if the
present V_TRIPx is 2.9V and the new V_TRIPx is 3.2V, the new
voltage can be stored directly into the V_TRIPx cell. If however,
the new setting is to be lower than the present setting, then it
is necessary to “reset” the V_TRIPx voltage before setting the
new value.
Setting a Higher V_TRIPx Voltage (x = 1, 2, 3)
To set a V_TRIPx threshold to a new voltage which is higher
than the present threshold, the user must apply the desired
V_TRIPx threshold voltage to the corresponding input pin
(Vcc(V1MON), V2MON or V3MON). Then, a programming
voltage (Vp) must be applied to the WDO pin before a START
condition is set up on SDA. Next, issue on the SDA pin the
Slave Address A0h, followed by the Byte Address 01h for
V_TRIP1, 09h for V_TRIP2, and 0Dh for V_TRIP3, and a 00h Data
Byte in order to program V_TRIPx. The STOP bit following a
valid write operation initiates the programming sequence. Pin
WDO must then be brought LOW to complete the operation.
To check if the V_TRIPX has been set, set VXMON to a value
slightly greater than V_TRIPX (that was previously set). Slowly
ramp down VXMON and observe when the corresponding
outputs (LOWLINE, V2FAIL and V3FAIL) switch. The voltage
at which this occurs is the V_TRIPX (actual).
CASE A
If the desired V_TRIPX is greater than the V_TRIPX (actual), then
add the difference between V_TRIPX (desired) – V_TRIPX
(actual) to the original V_TRIPX desired. This is your new
V_TRIPX that should be applied to VXMON and the whole
sequence should be repeated again (see Figure 5).
CASE B
If the V_TRIPX (actual), is higher than the V_TRIPX (desired),
perform the reset sequence as described in the next section.
8
FN8114.2
August 25, 2008