PIC16F648A-I Datasheet, PDF (14/34 Pages) Microchip Technology – Push-Pull Output Sub-Microamp Comparators

MCP6541/1R/1U/2/3/4
4.0 APPLICATIONS INFORMATION
The MCP6541/2/3/4 family of push-pull output compar-
ators are fabricated on Microchip’s state-of-the-art
CMOS process. They are suitable for a wide range of
applications requiring very low power consumption.
4.1 Comparator Inputs
4.1.1 PHASE REVERSAL
The MCP6541/1R/1U/2/3/4 comparator family uses
CMOS transistors at the input. They are designed to
prevent phase inversion when the input pins exceed
the supply voltages. Figure 2-3 shows an input voltage
exceeding both supplies with no resulting phase
inversion.
4.1.2
INPUT VOLTAGE AND CURRENT
LIMITS
The ESD protection on the inputs can be depicted as
shown in Figure 4-1. This structure was chosen to pro-
tect the input transistors, and to minimize input bias
current (IB). The input ESD diodes clamp the inputs
when they try to go more than one diode drop below
V_SS. They also clamp any voltages that go too far
above V_DD; their breakdown voltage is high enough to
allow normal operation, and low enough to bypass ESD
events within the specified limits.
V_DD
Bond
Pad
V_IN+
Bond
Pad
Input
Stage
Bond
Pad
V_IN–
V_SS
Bond
Pad
FIGURE 4-1:
Structures.
Simplified Analog Input ESD
In order to prevent damage and/or improper operation
of these amplifiers, the circuits they are in must limit the
currents (and voltages) at the V_IN+ and V_IN– pins (see
Absolute Maximum Ratings † at the beginning of
Section 1.0 “Electrical Characteristics”). Figure 4-3
shows the recommended approach to protecting these
inputs. The internal ESD diodes prevent the input pins
(V_IN+ and V_IN–) from going too far below ground, and
the resistors R₁ and R₂ limit the possible current drawn
out of the input pin. Diodes D₁ and D₂ prevent the input
pin (V_IN+ and V_IN–) from going too far above V_DD.
When implemented as shown, resistors R₁ and R₂ also
limit the current through D₁ and D₂.
V_DD
D₁
V₁
R₁
D₂
V₂
R₂
+
MCP6G0X
–
R₃
V_OUT
R₁
≥
V_SS
–
(minimum expected
2 mA
V₁)
R₂
≥
V_SS
–
(minimum expected
2 mA
V₂)
FIGURE 4-2: Protecting the Analog Inputs.
It is also possible to connect the diodes to the left of the
resistors R₁ and R₂. In this case, the currents through
the diodes D₁ and D₂ need to be limited by some other
mechanism. The resistor then serves as in-rush current
limiter; the DC current into the input pins (V_IN+ and
V_IN–) should be very small.
A significant amount of current can flow out of the
inputs when the common mode voltage (V_CM) is below
ground (V_SS); see Figure 2-37. Applications that are
high impedance may need to limit the useable voltage
range.
4.1.3 NORMAL OPERATION
The input stage of this family of devices uses two
differential input stages in parallel: one operates at low
input voltages and the other at high input voltages. With
this topology, the input voltage is 0.3V above V_DD and
0.3V below V_SS. Therefore, the input offset voltage is
measured at both V_SS - 0.3V and V_DD + 0.3V to ensure
proper operation.
The MCP6541/1R/1U/2/3/4 family has internally-set
hysteresis that is small enough to maintain input offset
accuracy (<7 mV) and large enough to eliminate output
chattering caused by the comparator’s own input noise
voltage (200 µV_p-p). Figure 4-3 depicts this behavior.
DS21696E-page 14
© 2006 Microchip Technology Inc.