16
FN8209.2
August 31, 2010
Setting a Lower V
TRIPx
Voltage (x = 1,2,3).
In order to set V
TRIPx
to a lower voltage than the
present value, then V
TRIPx
must first be “reset” accord-
ing to the procedure described below. Once V
TRIPx
has been “reset”, then V
TRIPx
can be set to the desired
voltage using the procedure described in “Setting a
Higher V
TRIPx
Voltage”.
Resetting the V
TRIPx
Voltage (x = 1,2,3).
To reset a V
TRIPx
voltage, apply the programming volt-
age (Vp) to the WP 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 03h for
V
TRIP1
, 0Bh for V
TRIP2
, and 0Fh for V
TRIP3
, followed
by 00h for the Data Byte in order to reset V
TRIPx
. The
STOP bit following a valid write operation initiates the
programming sequence. Pin WP must then be brought
LOW to complete the operation (See Figure 18).The
user does not have to set the WEL bit in the CON-
STAT register before performing this write sequence.
After being reset, the value of V
TRIPx
becomes a nomi-
nal value of 1.7V.
V
TRIPx
Accuracy (x = 1,2,3).
The accuracy with which the V
TRIPx
thresholds are set,
can be controlled using the iterative process shown in
Figure 19.
If the desired threshold is less that the present threshold
voltage, then it must first be “reset” (See "Resetting the
VTRIPx Voltage (x = 1,2,3)." ) .
The desired threshold voltage is then applied to the
appropriate input pin (V1/Vcc, V2 or V3) and the proce-
dure described in Section “Setting a Higher V
TRIPx
Voltage“ must be followed.
Once the desired V
TRIPx
threshold has been set, the
error between the desired and (new) actual set threshold
can be determined. This is achieved by applying V1/Vcc
to the device, and then applying a test voltage higher
than the desired threshold voltage, to the input pin of the
voltage monitor circuit whose V
TRIPx
was programmed.
For example, if V
TRIP2
was set to a desired level of 3.0V,
then a test voltage of 3.4 V may be applied to the voltage
monitor input pin V2. In the case of setting of V
TRIP1
then
only V1/Vcc need be applied. In all cases, care should be
taken not to exceed the maximum input voltage limits.
After applying the test voltage to the voltage monitor
input pin, the test voltage can be decreased (either in dis-
crete steps, or continuously) until the output of the volt-
age monitor circuit changes state. At this point, the error
between the actua measured, and desired threshold lev-
els is calculated.
For example, the desired threshold for V
TRIP2
is set to
3.0V, and a test voltage of 3.4V was applied to the input
pin V2 (after applying power to V1/Vcc). The input volt-
age is decreased, and found to trip the associated output
level of pin V2RO from a LOW to a HIGH, when V2
reaches 3.09V. From this, it can be calculated that the
programming error is 3.09 - 3.0 = 0.09V.
If the error between the desired and measured V
TRIPx
is
less than the maximum desired error, then the program-
ming process may be terminated. If however, the error is
greater than the maximum desired error, then another
iteration of the V
TRIPx
programming sequence can be
performed (using the calculated error) in order to further
increase the accuracy of the threshold voltage.
If the calculated error is greater than zero, then the
V
TRIPx
must first be “reset”, and then programmed to the
a value equal to the previously set V
TRIPx
minus the cal-
culated error. If it is the case that the error is less than
zero, then the V
TRIPx
must be programmed to a value
equal to the previously set V
TRIPx
plus the absolute value
of the calculated error.
Continuing the previous example, we see that the calcu-
lated error was 0.09V. Since this is greater than zero, we
must first “reset” the V
TRIP2
threshold, then apply a volt-
age equal to the last previously programmed voltage,
minus the last previously calculated error. Therefore, we
must apply V
TRIP2
= 2.91 V to pin V2 and execute the
programming sequence (See "Setting a Higher VTRIPx
Voltage (x = 1,2,3)" ) .
Using this process, the desired accuracy for a particu-
lar V
TRIPx
threshold may be attained using a succes-
sive number of iterations.
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