MAX965 데이터 시트보기 (PDF) - Maxim Integrated

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MAX965

Single/Dual/Quad, Micropower, Ultra-Low-Voltage, Rail-to-Rail I/O Comparators

Maxim Integrated 

Single/Dual/Quad, Micropower,

Ultra-Low-Voltage, Rail-to-Rail I/O Comparators

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 Hysteresis to the

MAX965/MAX967/MAX968/MAX969

To add hysteresis to the MAX965/MAX967/MAX968/

MAX969, connect resistor R1 between REF and HYST,

and connect resistor R2 between HYST and GND

(Figure 3). If additional hysteresis is not required,

connect HYST to REF. When hysteresis is added, the

upper and lower trip points change by the same

amount in opposite directions. The hysteresis band (the

difference between the upper and lower trip points,

VHB) is approximately twice the voltage between HYST

and REF. The HYST input voltage range is from REF

down to (REF - 50mV). This yields a hysteresis band

from ±1mV to a maximum of ±50mV. Calculate the val-

ues of R1 and R2 for the desired hysteresis band with

the following formulas:

R1 = VHB / IREF

R2 = (VREF - VHB) / IREF

where IREF (the current sourced by the reference) does

not exceed the REF source capability (12µA typical),

and is significantly larger than the HYST leakage cur-

rent (5nA typical). IREF values between 0.1µA and 4µA

are good choices. If 2.4MΩ is chosen for R2 (IREF =

0.5µA), the equation for R1 and VHB can be approxi-

mated as:

R1(kΩ) = 2 x VHB (mV)

In the MAX967/MAX968/MAX969, the HYST pin pro-

grams the same hysteresis for all comparators in the

package.

Due to the internal structure of the input developed for

ultra-low-voltage operation, the hysteresis band varies

with common-mode voltage. The graph Programmed

Hysteresis vs. Common-Mode Voltage in the Typical

Operating Characteristics shows this variation. Notice

that the hysteresis band increases to almost twice the

calculated value toward the ends of the common-mode

range. This is apparent only when programming addi-

tional hysteresis using the HYST pin. The hysteresis

band is constant when HYST is connected to REF.

Adding Hysteresis to the MAX966/MAX970

The MAX966/MAX970 do not have a HYST pin for pro-

gramming hysteresis. Hysteresis can be generated with

three resistors using positive feedback (Figure 4). This

method generally draws more current than the method

using the HYST pin on the MAX965/MAX967/MAX968/

MAX969. Also, the positive feedback method slows

hysteresis response time. Use the following procedure

to calculate the resistor values:

1) Select R3. The leakage current of IN+ is under 5nA,

so the current through R3 should be at least 500nA

to minimize errors caused by leakage current. The

current through R3 at the trip point is (VREF - VOUT) /

R3. Taking into consideration the two possible out-

put states and solving for R3 yields two formulas:

R3 = VREF / 500nA

and

R3 = (VREF - VCC) / 500nA

Use the smaller of the two resulting resistor values.

For example, if VREF = 1.2V and VCC = 5.0V, then

the two resistor values are 2.4MΩ and 7.6mΩ. For

R3, choose the 2.2MΩ standard value.

2) Choose the hysteresis band required (VHB). For this

example, choose 50mV.

IREF

R1

R2

+1.6V TO +5.5V

REF VCC

MAX965

MAX967

MAX968

MAX969

HYST

GND

R1

VIN

R2

VCC

R3

R4

VCC

OUT

GND

MAX966

VREF

MAX970

Figure 3. Programming the HYST Pin

Figure 4. External Hysteresis

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