X40420/X40421 – Preliminary
Figure 3. VTRIPX Set/Reset Conditions
(X = 1, 2)
Figure 4. Watchdog Restart
Data Byte in order to program VTRIPx. The STOP bit
following a valid write operation initiates the programming
sequence. Pin WDO must then be brought LOW to
complete the operation.
WDT Reset Stop
V1 AND V2 THRESHOLD PROGRAM PROCEDURE
The X40420/21 is shipped with standard V1 and V2
threshold (VTRIP1, VTRIP2) 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 X40420 trip points may be adjusted.
The procedure is described below, and uses the applica-
tion of a high voltage control signal.
Setting a VTRIPx Voltage (x=1, 2)
There are two procedures used to set the threshold volt-
ages (VTRIPx), depending if the threshold voltage to be
stored is higher or lower than the present value. For
example, if the present VTRIPx is 2.9 V and the new
VTRIPx is 3.2 V, the new voltage can be stored directly
into the VTRIPx cell. If however, the new setting is to be
lower than the present setting, then it is necessary to
“reset” the VTRIPx voltage before setting the new value.
Setting a Higher VTRIPx Voltage (x=1, 2)
To set a VTRIPx threshold to a new voltage which is higher
than the present threshold, the user must apply the
desired VTRIPx threshold voltage to the corresponding
input pin (Vcc(V1MON) or V2MON). Then, a program-
ming 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 VTRIP1, and 09h for VTRIP2, and a 00h
To check if the VTRIPX has been set, set VXMON to a
value slightly greater than VTRIPX (that was previously
set). Slowly ramp down VXMON and observe when the
corresponding outputs (LOWLINE and V2FAIL) switch.
The voltage at which this occurs is the VTRIPX (actual).
Now if the desired VTRIPX is greater than the VTRIPX
(actual), then add the difference between VTRIPX
(desired) – VTRIPX (actual) to the original VTRIPX desired.
This is your new VTRIPX that should be applied to
VXMON and the whole sequence should be repeated
again (see Figure 5).
Now if the VTRIPX (actual), is higher than the VTRIPX
(desired), perform the reset sequence as described in the
next section. The new VTRIPX voltage to be applied to
VXMON will now be: VTRIPX (desired) – (VTRIPX (actual)
– VTRIPX (desired)).
Note: 1. This operation does not corrupt the memory
2. Set VCC = 5V, when VTRIP2 is being pro-
Setting a Lower VTRIPx Voltage (x=1, 2)
In order to set VTRIPx to a lower voltage than the
present value, then VTRIPx must ﬁrst be “reset” accord-
ing to the procedure described below. Once VTRIPx
has been “reset”, then VTRIPx can be set to the desired
voltage using the procedure described in “Setting a
Higher VTRIPx Voltage”.
REV 1.2.14 7/12/02
Characteristics subject to change without notice. 5 of 25