MIC842LYMT(2015) 查看數據表（PDF） - Micrel
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MIC842LYMT Datasheet PDF : 11 Pages
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Micrel, Inc.
Application Information
Output
The MIC841N and MIC842N outputs are an open-drain
MOSFET, so most applications will require a pull-up
resistor. The value of the resistor should not be too large
or leakage effects may dominate. 470kΩ is the maximum
recommended value. Note that the output of “N” version
may be pulled up as high as 6V regardless of the ICs
supply voltage. The “H” and “L” versions of the MIC841
and MIC842 have a push-pull output stage, with a diode
clamped to VDD. Thus, the maximum output voltage of
the “H” and “L” versions is VDD (see Electrical
Characteristics).
When working with large resistors on the input to the
devices, a small amount of leakage current can cause
voltage offsets that degrade system accuracy. The
maximum recommended total resistance from VIN to
ground is 3MΩ. The accuracy of the resistors can be
chosen based upon the accuracy required by the system.
The inputs may be subjected to voltages as high as 6V
steady-state without adverse effects of any kind
regardless of the ICs supply voltage. This applies even if
the supply voltage is zero. This permits the situation in
which the IC’s supply is turned off, but voltage is still
present on the inputs (see Electrical Characteristics).
Programming the MIC841 Thresholds
The low-voltage threshold is calculated using Equation 1:
VIN(LO) =
VREF
R1+ R2 + R3
R2 + R3
Eq. 1
The high-voltage threshold is calculated using Equation
2:
VIN(HI)
=
VREF
R1+
R2 +
R3
R3
Eq. 2
Where, for both equations:
VREF = 1.240V
MIC841/842
In order to provide the additional criteria needed to solve
for the resistor values, the resistors can be selected such
that they have a given total value, that is, R1 + R2 + R3 =
RTOTAL. A value such as 1MΩ for RTOTAL is a reasonable
value because it draws minimum current but has no
significant effect on accuracy.
Figure 1. MIC841 Example Circuit
Once the desired trip points are determined, set the VIN(HI)
threshold first.
For example, use a total of 1MΩ = R1 + R2 + R3. For a
typical single-cell lithium ion battery, 3.6V is a good “high
threshold” because at 3.6V the battery is moderately
charged. Solving for R3:
VIN(HI)
=
3.6V
=
1.24V
1MΩ
R3
Eq. 3
Where:
R3 = 344kΩ
Once R3 is determined, the equation for VIN(LO) can be
used to determine R2. A single lithium-ion cell, for
example, should not be discharged below 2.5V. Many
applications limit the drain to 3.1V.
July 24, 2015
6
Revision 5.0
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