MAX934CSE データシートの表示（PDF） - Maxim Integrated

部品番号

コンポーネント説明

メーカー

MAX934CSE

Ultra Low-Power, Low-Cost Comparators with 2% Reference

Maxim Integrated 

Ultra Low-Power, Low-Cost

Comparators with 2% Reference

Board Layout and Bypassing

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.

_______________Typical Applications

Auto-Off Power Source

Figure 5 shows the schematic for a 40mA power supply

that has a timed auto power-off function. The

comparator output is the switched power-supply output.

With a 10mA load, it typically provides a voltage of

(VBATT - 0.12V), but draws only 3.5µA quiescent current.

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:

R x C x 4.6sec

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.

Window Detector

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

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 (VH = VHB/2). This means

that the hysteresis apparent at VIN will be larger

because of the input resistor divider.

2. Select R1. The leakage current into INB- is normally

under 1nA, so the current through R1 should exceed

4.5V TO 6.0V

7

V+

MOMENTARY SWITCH

6 REF

MAX931

IN+ 3

47k

5 HYST

1.1M

4 IN-

100k

V-

2

C

R

OUT 8

GND

1

VBATT -0.15V

10mA

VIN

R3

VOTH = 5.5V

VUTH = 4.5V

INA+

+5V

V+

OUTA

HYST

R2

R5

10k REF

OUTB

INB-

R1

R4

2.4M

V- MAX933

UNDERVOLTAGE

POWER GOOD

OVERVOLTAGE

Figure 5. Auto-off power switch operates on 2.5µA quiescent

current.

Figure 6. Window Detector

______________________________________________________________________________________ 11

Share Link: