TK65010 データシートの表示（PDF） - Toko America Inc
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TK65010 Datasheet PDF : 8 Pages
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TK65010
DESIGN CONSIDERATIONS
In order to design a voltage monitor utilizing the TK65010,
the two external resistors comprising the resistor divider
must be properly selected. Selecting the ratio of the
resistors will establish the lower monitoring threshold
(DBO). Selecting the value of the R1 will establish the
upper monitoring threshold (LBO) relative to the lower
(DBO) threshold. The value of R2 will be dictated by the
ratio R1/R2 and the value of R1. For the following
explanations, please refer to the circuit diagram of
Figure 3.
SETTING THE DBO THRESHOLD
As mentioned above, the ratio of R1/R2 established the
”dead battery” threshold. The dead battery comparator
trips when the voltage on the VMON pin passes through
approximately 690 mV and the current into the VMON pin is
approximately zero. Given the required dead battery
threshold, the ratio R1/R2 can be selected utilizing the
following equation:
DBO Threshold = 690 mV x (1 + R1/R2)
or
R1/R2 = (DBO Threshold - 690 mV) / 690 mV
RESISTOR TOLERANCE CONSIDERATIONS
The tolerance of the LBO and DBO thresholds will have a
significant dependence upon the tolerance of the resistive
components used in the resistor divider. When utilizing the
previously described equations for setting the LBO and
DBO thresholds, it is possible that optimal values of the
resistive elements R1 and R2 may be relatively large. Since
large resistive components are not always available with
tight tolerances, an alternate method can be used for
applications where tighter tolerances are required.
The purpose of the resistor divider connected between the
Battery Input and the VMON pin is twofold. The first purpose
is to appropriately select the divider ratio such that the
DBO threshold is set to the desired level. The second
purpose is to select the absolute resistor values such that
the LBO threshold is set to an appropriate level relative to
the DBO threshold. Effectively, an attenuated voltage
source with a relatively large output impedance is driving
the VMON pin. This scenario is illustrated in Figure 4.
VIN
R1
SETTING THE LBO THRESHOLD
The threshold of the LBO comparator will be at a value
greater than the DBO threshold. The value of resistor
value R1 dictates the difference between the LBO and
DBO thresholds as follows:
VMON
R2
LBO Threshold = DBO Threshold x 1.029 + R1 x 580 nA
or
R1 = (LBO Threshold - DBO Threshold x 1.029) / 580 nA
BATTERY IN
R1
VIN
GND
VMON
R2
IFB
LBO
DBO
LOW BATTERY
DEAD BATTERY
R1 x R2
R1 + R2
+
VIN x R2
R1 + R2
VMON
FIGURE 4
FIGURE 3
January 1999 TOKO, Inc.
Page 5
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