LTC6255 datasheet(18/30 Pages) LINER

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LTC6752/LTC6752-1/

LTC6752-2/LTC6752-3/

LTC6752-4

6752fc

For more information www.linear.com/LTC6752

applicaTions inForMaTion

Input Protection

The input stage is protected against damage from condi-

tions where the voltage on either pin exceeds the supply

voltage (VCC to VEE) without external protection. External

input protection circuitry is only needed if input currents

can exceed the absolute maximum rating. For example,

if an input is taken beyond 300mV of either the positive

or negative supply, an internal ESD protection diode will

conduct and an external resistor should be used to limit

the current to less than 10mA.

Outputs

The LTC6752 family has excellent drive capability. The

comparators can deliver typically ±22mA output current

for an output supply of 2.5V, and ±39mA output current

for a 3.3V output supply. Attention must be paid to keep

the junction temperature of the IC below 150°C should the

output have a continuous short-circuit condition.

Logic Drive Capability

The LTC6752 family has been designed to drive CMOS

logic with a supply of 3.3V, 2.5V and 1.8V. For device reli-

ability,theoutputpowersupply(VDD)shouldnotbehigher

than 3.6V above the negative supply. When VDD is 3V or

higher the CMOS outputs of the LTC6752 family provide

valid TTL logic threshold levels and can easily interface

with TTL logic devices operating with a 5V supply. This is

possiblebecauseallofthethresholdlevelsassociatedwith

TTL logic (VIH/VIL/VOH/VOL) are less than or equal to 2.4V

Capacitive Loads

The LTC6752 family can drive capacitive loads. Transient

performance parameters in the Electrical Characteristics

Tables and Typical Characteristics section are for a load

of 5pF, corresponding to a standard TTL/CMOS load. The

devices are fully functional for larger capacitive loads,

howeverspeedperformancewilldegrade.Thegraphstitled

Propagation Delay vs Capacitive Load and Toggle Rate vs

CapacitiveLoadillustratetheimpactofchangestothetotal

capacitive load. For optimal speed performance, output

load capacitance should be reduced as much as possible.

ESD

The LTC6752 family members have reverse-biased ESD

protection diodes on pins as shown in Figure 1.

There are additional clamps between the positive and

negative supplies that further protect the device during

ESD strikes. Hot-plugging of the device into a powered

socketisnotrecommendedsincethiscantriggertheclamp

resultinginlargecurrentsflowingbetweenthesupplypins.

Hysteresis

Comparators have very high open-loop gain. With slow

input signals that are close to each other, input noise can

cause the output voltage to switch randomly. This can be

addressed by hysteresis which is positive feedback that

increases the trip point in the direction of the input signal

transition when the output switches. This pulls the inputs

away from each other, and prevents continuous switching

back and forth. The addition of positive feedback also has

theeffectofmakingthesmallsignalgaininfinitearoundthe

trip points. Hysteresis is designed into most comparators

and the LTC6752 family has adjustable hysteresis with a

default hysteresis of 5mV.

The input-output transfer characteristic is illustrated in

Figure 3 showing the definitions of VOS and HYST based

upon the two measurable trip points.

In some cases, additional noise immunity is required

above what is provided by the nominal 5mV hysteresis.

Figure 3

VOH

VOL

VOS =

6752 F03

VOUT

VOS

VTRIP+

VHYST

(= VTRIP+ – VTRIP–)

∆VIN = VIN+ – VIN–

VTRIP+ + VTRIP–

VTRIP–

FOR VTRIP+ = 3mV,

VTRIP– = –2mV,

VOS = 0.5mV,

VHYST = 5mV

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