MAX933CUA+ Maxim Integrated Products, MAX933CUA+ Datasheet - Page 11

• Manufacturer Part Number: MAX933CUA+
• Description: IC COMPARATOR W/REF 8-UMAX
• Manufacturer: Maxim Integrated Products
• Type: with Voltage Referencer

Specifications of MAX933CUA+

• Number Of Elements: 2
• Output Type: CMOS, TTL
• Voltage - Supply: 2.5 V ~ 11 V, ±1.25 V ~ 5.5 V
• Mounting Type: Surface Mount
• Package / Case: 8-TSSOP, 8-MSOP (0.118", 3.00mm Width)
• Number Of Channels: 2 Channels
• Supply Voltage (max): 5.5 V
• Supply Voltage (min): 1.25 V
• Supply Current (max): 4.5 uA
• Maximum Operating Temperature: + 70 C
• Mounting Style: SMD/SMT
• Minimum Operating Temperature: 0 C
• Propagation Delay Time: 12 us
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Power-supply bypass capacitors are not needed if the
supply impedance is low, but 100nF bypass capacitors
should be used when the supply impedance is high or
when the supply leads are long. Minimize signal lead
lengths to reduce stray capacitance between the input
and output that might cause instability. Do not bypass
the reference output.
Figure 5 shows the schematic for a 40mA power supply
that has a timed auto power-off function.
comparator output is the switched power-supply output.
With a 10mA load, it typically provides a voltage of
(V
This circuit takes advantage of the four key features of
the MAX931: 2.5µA supply current, an internal
reference, hysteresis, and high current output. Using
the component values shown, the three-resistor voltage
divider programs the maximum ±50mV of hysteresis
and sets the IN- voltage at 100mV. This gives an IN+
trip threshold of approximately 50mV for IN+ falling.
The RC time constant determines the maximum power-
on time of the OUT pin before power-down occurs.
This period can be approximated by:
Figure 5. Auto-off power switch operates on 2.5µA quiescent
current.
_______________Typical Applications
BATT
1.1M
100k
47k
- 0.12V), but draws only 3.5µA quiescent current.
4.5V TO 6.0V
R x C x 4.6sec
6
5
4
HYST
REF
IN-
______________________________________________________________________________________
Board Layout and Bypassing
2
V-
MAX931
7
V+
Auto-Off Power Source
GND
1
OUT
IN+
MOMENTARY SWITCH
Comparators with 2% Reference
8
3
C
VBATT -0.15V
10mA
Ultra Low-Power, Low-Cost
The
R
For example: 2MΩ x 10µF x 4.6 = 92sec. The actual
time will vary with both the leakage current of the
capacitor and the voltage applied to the circuit.
The MAX933 is ideal for making window detectors
(undervoltage/overvoltage detectors). The schematic
is shown in Figure 6, with component values selected
for an 4.5V undervoltage threshold, and a 5.5V
overvoltage threshold. Choose different thresholds by
changing the values of R1, R2, and R3. To prevent
chatter at the output when the supply voltage is close
to a threshold, hysteresis has been added using R4
and R5. OUTA provides an active-low undervoltage
indication, and OUTB gives an active-low overvoltage
indication. ANDing the two outputs provides an active-
high, power-good signal.
The design procedure is as follows:
1. Choose the required hysteresis level and calculate
2. Select R1. The leakage current into INB- is normally
Figure 6. Window Detector
R2
R3
R1
values for R4 and R5 according to the formulas in
the Hysteresis (MAX931/MAX932/MAX933) section.
In this example, ±5mV of hysteresis has been added
at the comparator input (V
that the hysteresis apparent at V
because of the input resistor divider.
under 1nA, so the current through R1 should exceed
V
IN
V
V
R4
2.4M
OTH
UTH
10k
R5
= 5.5V
= 4.5V
HYST
REF
INB-
INA+
V-
+5V
V+
MAX933
OUTA
OUTB
H
= V
Window Detector
HB
IN
/2). This means
will be larger
UNDERVOLTAGE
POWER GOOD
OVERVOLTAGE
11