MAX9025 데이터 시트보기 (PDF) - Maxim Integrated

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MAX9025

UCSP, 1.8V, Nanopower, Beyond-the-Rails Comparators With/Without Reference

Maxim Integrated 

MAX9025–MAX9028

UCSP, 1.8V, Nanopower, Beyond-the-Rails

Comparators With/Without Reference

Reference (MAX9025/MAX9026)

The MAX9025−MAX9028s’ internal +1.236V reference

has a typical temperature coefficient of 40ppm/ºC over

the full -40ºC to +85ºC temperature range. The reference

is a very-low-power bandgap cell, with a typical 35kΩ

output impedance. REF can source and sink up to 100nA

to external circuitry. For applications needing increased

drive, buffer REF with a low input-bias current op amp

such as the MAX4162. Most applications require no REF

bypass capacitor. For noisy environments or fast VCC

transients, connect a 1nF to 10nF ceramic capacitor from

REF to GND.

Applications Information

Low-Voltage, Low-Power Operation

The MAX9025−MAX9028 are ideally suited for use with

most battery-powered systems. Table 1 lists a variety of

battery types, capacities, and approximate operating times

for the MAX9025−MAX9028, assuming nominal conditions.

Internal Hysteresis

Many comparators oscillate in the linear region of opera-

tion because of noise or undesired parasitic feedback.

This tends to occur when the voltage on one input is

equal or very close to the voltage on the other input. The

MAX9025−MAX9028 have internal 4mV hysteresis to

counter parasitic effects and noise.

The hysteresis in a comparator creates two trip points:

one for the rising input voltage (VTHR) and one for the

falling input voltage (VTHF) (Figure 2). The difference

between the trip points is the hysteresis (VHB). When

the comparator’s input voltages are equal, the hysteresis

VCC

BANDGAP

REF

VEE

Figure 1. MAX9025/MAX9026 Voltage Reference Output

Equivalent Circuit

effectively causes one comparator input to move quickly

past the other, thus taking the input out of the region

where oscillation occurs. Figure 2 illustrates the case in

which IN- has a fixed voltage applied, and IN+ is varied.

If the inputs were reversed, the figure would be the same,

except with an inverted output.

Adding External Hysteresis

In applications requiring more than the internal 4mV hys-

teresis of the MAX9025−MAX9028, additional hysteresis

can be added with external components. Because the

MAX9025−MAX9028 are intended for very low-power

systems, care should be taken to minimize power dissipa-

tion in the additional circuitry.

Regardless of which approach is taken, the external hys-

teresis will be VCC dependent. Over the full discharge

range of battery-powered systems, the hysteresis can

change as much as 40%. This must be considered

during design.

Table 1. Battery Applications Using MAX9025−MAX9028

BATTERY

TYPE

RECHARGEABLE

VFRESH

(V)

Alkaline

(2 Cells)

No

3.0

VEND-OF-LIFE

(V)

CAPACITY,

AA SIZE

(mA-h)

MAX9025/MAX9026

OPERATING TIME

(hr)

MAX9027/MAX9028

OPERATING TIME

(hr)

1.8

2000

1.8 x 106

2.8 x 106

Nickel-

Cadmium

Yes

(2 Cells)

2.4

1.8

750

680,000

1.07 x 106

Lithium-Ion

(1 Cell)

Yes

3.5

2.7

1000

0.9 x 106

1.4 x 106

Nickel-Metal-

Hydride

Yes

(2 Cells)

2.4

1.8

1000

0.9 x 106

1.4 x 106

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