MAX919 데이터 시트보기 (PDF) - Maxim Integrated

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MAX919

SOT23, 1.8V, Nanopower, Beyond-the-Rails Comparators With/Without Reference

Maxim Integrated 

SOT23, 1.8V, Nanopower, Beyond-the-Rails

Comparators With/Without Reference

Output Stage Circuitry

The MAX917–MAX920 contain a unique break-before-

make output stage capable of rail-to-rail operation with

up to ±8mA loads. Many comparators consume orders

of magnitude more current during switching than dur-

ing steady-state operation. However, with this family of

comparators, the supply-current change during an out-

put transition is extremely small. In the Typical Oper-

ating Characteristics, the Supply Current vs. Output

Transition Frequency graphs show the minimal supply-

current increase as the output switching frequency

approaches 1kHz. This characteristic reduces the need

for power-supply filter capacitors to reduce glitches

created by comparator switching currents. In battery-

powered applications, this characteristic results in a

substantial increase in battery life.

Reference (MAX917/MAX918)

The internal reference in the MAX917/MAX918 has an

output voltage of +1.245V with respect to VEE. Its typi-

cal temperature coefficient is 95ppm/°C over the full

-40°C to +85°C temperature range. The reference is a

PNP emitter-follower driven by a 120nA current source

(Figure 1). The output impedance of the voltage refer-

ence is typically 200kΩ, preventing the reference from

driving large loads. The reference can be bypassed

with a low-leakage capacitor. The reference is stable

for any capacitive load. For applications requiring a

lower output impedance, buffer the reference with a

low-input-leakage op amp, such as the MAX406.

Applications Information

Low-Voltage, Low-Power Operation

The MAX917–MAX920 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 MAX917–MAX920, assuming nominal conditions.

VCC

120nA

REF

VEE

Figure 1. MAX917/MAX918 Voltage Reference Output

Equivalent Circuit

Internal Hysteresis

Many comparators oscillate in the linear region of oper-

ation because of noise or undesired parasitic feed-

back. This tends to occur when the voltage on one

input is equal or very close to the voltage on the other

input. The MAX917–MAX920 have internal 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 hystere-

sis 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.

Table 1. Battery Applications Using MAX917–MAX920

BATTERY

TYPE

RECHARGEABLE

VFRESH

(V)

VEND-OF-LIFE

(V)

CAPACITY, MAX917/MAX918

AA SIZE OPERATING TIME

(mA-h)

(hr)

Alkaline

(2 Cells)

No

3.0

1.8

2000

2.5 x 106

Nickel-Cadmium

(2 Cells)

Yes

2.4

1.8

750

937,500

Lithium-Ion

(1 Cell)

Yes

3.5

2.7

1000

1.25 x 106

Nickel-Metal-

Hydride

Yes

(2 Cells)

2.4

1.8

1000

1.25 x 106

MAX919/MAX920

OPERATING TIME

(hr)

5 x 106

1.875 x 106

2.5 x 106

2.5 x 106

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