LTC6754ISC6#TRMPBF datasheet(13/22 Pages) AD

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LTC6754

6754f

For more information www.linear.com/LTC6754

applicaTions inForMaTion

TheLE/HYSTpincanbemodeledasa1.25Vvoltagesource

in series with a 15kΩ resistor. The simplest method to in-

creasetheinternalhysteresisistoconnectasingleresistor

between the LE/HYST pin and VEE to adjust hysteresis as

shown in Figure 4. Figure 5 shows how hysteresis typically

varies with the value of the resistor.

6754 F04

VCCI

VCCO

VEE

LE/HYST

–IN

+IN

–

Figure 4. Adjusting Hysteresis Using an External

Resistor at the LE/HYST Pin

CONTROL RESISTANCE (kΩ)

25 75 125 175 225 275 325 375 425 475

6754 F05

VCC = 5V

CONTROL RESISTOR CONNECTED

BETWEEN LE/HYST AND VEE

Figure 5. Hysteresis vs Control Resistance

Alternatively, additional hysteresis can be added by using

positive feedback as shown in Figure 6.

100

–

VREF

SIGNAL

6754 F06

Figure 6. Additional Hysteresis Using positive Feedback

The offset and hysteresis become:

VOS_FB ≈

VREFR1+ VCMR2

+R2

+ VOS

VHYST_FB ≈

VODR2

+R2

+ VHYST

VOS_FB and VHYST_FB denote the values of offset and

hysteresis with positive feedback present. VHYST denotes

the hysteresis of the device without positive feedback.

VOCM and VOD are defined in the Electrical Characteristics

Tables. Additional inaccuracies are introduced by ΔVOD

and ΔVOCM, which are typically less than 5mV and 1.8mV,

respectively. They typically will introduce only a few mV

of error, which may be acceptable for large hysteresis

settings in many applications.

InordertoensurethatVODdoesnotdeviatetoomuchfrom

its value without positive feedback, R1 and R2 should be

chosen such that the current through them is much less

than 3.5mA by at least an order of magnitude. Extremely

high resistance values however can degrade transient

performance because of the phase shift caused by the

resistors and device input capacitance.

For VREF = 0V, VEE = 0V, an increase in hysteresis of ap-

proximately 100mV can be obtained with R1 = 7.5kΩ and

R2 = 3.01kΩ, assuming VOD = 350mV and VOCM = 1.25V.

Offset induced is approximately 350mV. Similarly for

VREF = 1.25V, R2 = 5.9kΩ, R1 = 3.01kΩ, additional hys-

teresis of approximately 230mV can be obtained with an

offset of approximately 1.25V.

LTC6754ISC6#TRMPBF 数据表(PDF) 13 Page - Analog Devices

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