MAX44268 Maxim, MAX44268 Datasheet - Page 11

• Manufacturer Part Number: MAX44268
• Description: The MAX44268 is an ultra-small and low-power dual comparator ideal for battery-powered applications such as cell phones, notebooks, and portable medical devices that have extremely aggressive board space and power constraints
• Manufacturer: Maxim

The IC can be used to make a power-on-reset circuit as
displayed in
ratiometric reference with respect to the power supply
and is created by a simple resistive divider. Choose
reasonably large values to minimize the power consump-
tion in the resistive divider. The positive input provides
the power-on delay time set by the time constant of the
RC circuit formed by R2 and C1. This simple circuit can
be used to power up the system in a known state after
ensuring that the power supply is stable. Diode D1 pro-
vides a rapid reset in the event of unexpected power loss.
If using comparator A, R3 and R4 are not populated and
REF settles in approximately 100µs.
The IC can also be used to make a simple relaxation
oscillator
RC circuit R5 and C1, a standard Schmidt Trigger circuit
referenced to a set voltage is converted into an astable
Figure 4. Logic-Level Translator
Figure 5. Power-On Reset Circuit
R3
R4
V
CC
(Figure
D1
Figure
V
V
REF
IN
C1
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6) using comparator B. By adding the
R2
5. The negative input provides the
MAX44268
V
CC
Power-On-Reset Circuit
GND
MAX44268
Relaxation Oscillator
V
CC
GND
OUT
V
PULL
R1
Dual Comparator with Reference
RESET
R1
1.3mm x 1.3mm, Low-Power
multivibrator. As shown in
waveform with capacitor C1 alternately charging and
discharging through resistor R5. The external hysteresis
network formed by R1 to R4 defines the trip voltages as:
Using the basic time domain equations for the charging
and discharging of an RC circuit, the logic-high time,
logic-low time, and frequency can be calculated as:
Since the comparator’s output is open drain, it goes to
high impedance corresponding to logic-high. So, when
the output is at logic-high, the C1 capacitor charges
through the resistor network formed by R1 to R5. An
accurate calculation of t
applying thevenin’s theorem to compute the equivalent
thevenin voltage (V
Figure 6. Relaxation Oscillator
V
T_FALL
R2
R4
V
V
CC
T_RISE
C1
=
t
V
LOW
CC
=
V
THEVENIN
R3







=
CC
R4R5 (R1 R2 R3) R1R3R4
R5C1 ln
MAX44268
+



R2(R1R3 R3R5 R1R5)
R2R3 R2R4 R3R4
V
R4R5(R1 R2 R3)
R5
HIGH
CC
Figure
GND
) and thevenin resistance




+
+
V
+
V
MAX44268
R3 x R4
T_FALL
T_RISE
R1R3R4
+
would have involved
7, IN- is a sawtooth
+
+
OUT
+




+
+
+



R1






