MAX44268 View Datasheet(PDF) - Maxim Integrated
Part Name
Description
Manufacturer
MAX44268 Datasheet PDF : 15 Pages
| |||
MAX44268
1.3mm x 1.3mm, Low-Power
Dual Comparator with Reference
Power-On-Reset Circuit
The IC can be used to make a power-on-reset circuit as
displayed in Figure 5. The negative input provides the
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.
Relaxation Oscillator
The IC can also be used to make a simple relaxation
oscillator (Figure 6) using comparator B. By adding the
RC circuit R5 and C1, a standard Schmidt Trigger circuit
referenced to a set voltage is converted into an astable
VCC
MAX44268
VIN
VPULL
R1
OUT
VREF
multivibrator. As shown in Figure 7, IN- is a sawtooth
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:
VT
_RISE
=
VCC
R2R3
R3 x R4
+ R2R4 +
R3R4
R4R5(R1+ R2 + R3)
V T _FALL
=
VCC
R4R5
(R1
+ R1R3R4
+ R2 + R3)
+
R1R3R4
+ R2(R1R3 + R3R5 + R1R5)
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:
tLOW
=
R5C1
ln
V T _FALL
V T _RISE
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 tHIGH would have involved
applying thevenin’s theorem to compute the equivalent
thevenin voltage (VTHEVENIN) and thevenin resistance
GND
Figure 4. Logic-Level Translator
VCC
VCC
D1 R2
R3
MAX44268
R1
RESET
R4
C1
GND
VCC
R2
R4
VCC
R3
MAX44268
R1
OUT
GND
R5
C1
Figure 5. Power-On Reset Circuit
Figure 6. Relaxation Oscillator
���������������������������������������������������������������� Maxim Integrated Products 11
Share Link: 