16
FN8208.2
September 7, 2010
Setting a Higher V
TRIPx
Voltage (x = 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 (V2 or V3). Then, a pro-
gramming voltage (Vp) must be applied 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 09h for V
TRIP3
, 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 WP must then be brought LOW to
complete the operation (See Figure 16). The user
does not have to set the WEL bit in the CONSTAT
register before performing this write sequence.
Setting a Lower V
TRIPx
Voltage (x = 2,3)
In order to set V
TRIPx
to a lower voltage than the
present value, then V
TRIPx
must first be “reset”
according 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
To reset a V
TRIPx
voltage, apply the programming
voltage (Vp) to the WP pin before a START condi-
tion is set up on SDA. Next, issue on the SDA pin
the Slave Address A0h followed by the Byte
Address 0Bh for V
TRIP2
, and 0Fh for V
TRIP3
, fol-
lowed by 00h for the Data Byte in order to reset
V
TRIPx
. The STOP bit following a valid write opera-
tion initiates the programming sequence. Pin WP
must then be brought LOW to complete the opera-
tion (See Figure 16).The user does not have to set
the WEL bit in the CONSTAT register before per-
forming this write sequence.
After being reset, the value of V
TRIPx
becomes a
nominal value of 1.7V.
V
TRIPx
Accuracy (x = 2,3)
The accuracy with which the V
TRIPx
thresholds are
set, can be controlled using the iterative process
shown in Figure 17.
If the desired threshold is less that the present
threshold voltage, then it must first be “reset” (See
"Resetting the VTRIPx Voltage").
The desired threshold voltage is then applied to
the appropriate input pin (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 Vcc / V1 to the device, and then applying
a test voltage higher than the desired threshold
voltage, to the input pin of the voltage monitor cir-
cuit whose V
TRIPx
was programmed. For example,
if V
TRIP2
was set to a desired level of 3.0 V, then a
test voltage of 3.4 V may be applied to the voltage
monitor input pin V2. In all cases, care should be
taken not to exceed the maximum input voltage
limits.
After applying the test voltage to the voltage moni-
tor input pin, the test voltage can be decreased
(either in discrete steps, or continuously) until the
output of the voltage monitor circuit changes
state. At this point, the error between the actual /
measured, and desired threshold levels is calcu-
lated.
For example, the desired threshold for V
TRIP2
is
set to 3.0 V, and a test voltage of 3.4 V was applied
to the input pin V2 (after applying power to Vcc /
V1). The input voltage is decreased, and found to
trip the associated output level of pin V2RO from a
LOW to a HIGH, when V2 reaches 3.09 V. From
this, it can be calculated that the programming
error is 3.09 - 3.0 = 0.09 V.
If the error between the desired and measured
V
TRIPx
is less than the maximum desired error,
then the programming 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 pro-
grammed to the a value equal to the previously set
V
TRIPx
minus the calculated 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 previ-
ously set V
TRIPx
plus the absolute value of the cal-
culated error.
Continuing the previous example, we see that the
calculated error was 0.09V. Since this is greater
than zero, we must first “reset” the V
TRIP2
thresh-
old, then apply a voltage equal to the last previ-
ously programmed voltage, minus the last
previously calculated error. Therefore, we must
apply V
TRIP1
= 2.91 V to pin V2 and execute the
programming sequence (See "Setting a Higher
VTRIPx Voltage (x = 2,3)" ) .
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