MAX9144EUD 데이터 시트보기 (PDF) - Maxim Integrated

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MAX9144EUD

40ns, Low-Power, 3V/5V, Rail-to-Rail Single-Supply Comparators

Maxim Integrated 

40ns, Low-Power, 3V/5V, Rail-to-Rail

Single-Supply Comparators

Detailed Description

The MAX9140/MAX9141/MAX9142/MAX9144 single-

supply comparators feature internal hysteresis, high

speed, and low power. Their outputs are pulled to with-

in 300mV of either supply rail without external pullup or

pulldown circuitry. Rail-to-rail input voltage range and

low-voltage single-supply operation make these

devices ideal for portable equipment. The

MAX9140/MAX9141/MAX9142/MAX9144 interface

directly to CMOS and TTL logic.

Most high-speed comparators oscillate in the linear

region because of noise or undesired parasitic feed-

back. This tends to occur when the voltage on one

input is at or equal to the voltage on the other input. To

counter the parasitic effects and noise, the MAX9140/

MAX9141/MAX9142/MAX9144 have an internal hystere-

sis of 1.5mV.

The hysteresis in a comparator creates two trip points:

one for the rising input voltage and one for the falling

input voltage (Figure 1). The difference between the trip

points is the hysteresis. The average of the trip points is

the offset voltage. When the comparator’s input volt-

ages are equal, the hysteresis effectively causes one

comparator input voltage to move quickly past the

other, thus taking the input out of the region where

oscillation occurs. Standard comparators require hys-

teresis to be added with external resistors. The

MAX9140/MAX9141/MAX9142/MAX9144’s fixed internal

hysteresis eliminates these resistors. To increase hys-

teresis and noise margin even more, add positive feed-

back with two resistors as a voltage divider from the

output to the noninverting input.

Figure 1 illustrates the case where IN- is fixed and IN+

is varied. If the inputs were reversed, the figure would

look the same, except the output would be inverted.

iTsnthpoeruatMgimeApXoe9f d1ca4on1mcpein.acrIlifsuL—odEnesirseashnuigltihsn,.tetThrhneealalL—tlEcahtpciihsn

that allows

has a high

transparent

(i.e., the comparator operates as though the latch is not

pwrheesneL—nEt)i.s

The comparator's output

pulled low (Figure 2).

state

is

latched

Shutdown Mode (MAX9141 Only)

The MAX9141 shuts down when the –S—H—D—N– pin is low.

When shut down, the supply current drops to less than

C1ad2nooµwcnAenn,e. wacTntihtdhS—eH—tL—h–DS——EeNH–—htDh—tiogNr–ehVepC-(istnCrtaahnftoeasrpsonauaortpermhnuittagblsheto-acpitnoeepm)r;auetotisotihnmhe.igprEwhexidsiimteas,pnhectuhdete--.

output will be indeterminate.

VTRIP+

VHYST

VTRIP-

COMPARATOR

OUTPUT

VIN+

VOS =

VTRIP+ + VTRIP-

2

VIN- = 0

VOH

VOL

Figure 1. Input and Output Waveform, Noninverting Input

Varied

Input Stage Circuitry

The MAX9140/MAX9141/MAX9142/MAX9144 include

internal protection circuitry that prevents damage to the

precision input stage from large differential input volt-

ages. This protection circuitry consists of two back-to-

back diodes between IN+ and IN- as well as two series

4.1kΩ resistors (Figure 3). The diodes limit the differen-

tial voltage applied to the internal circuitry of the com-

parators to be no more than 2VF, where VF is the for-

ward voltage drop of the diode (about 0.7V at +25°C).

For a large differential input voltage (exceeding 2VF),

this protection circuitry increases the input bias current

at IN+ (source) and IN- (sink).

Input Current = (IN+ - IN-) - 2VF

2 x 4.1kΩ

Input current with large differential input voltages

should not be confused with input bias current (IB). As

long as the differential input voltage is less than 2VF,

this input current is equal to IB. The output is in the cor-

rect logic state if one or both inputs are within the com-

mon-mode range.

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