LTC1040MJ View Datasheet(PDF) - Linear Technology

Part Name

Description

Manufacturer

LTC1040MJ

Dual Micropower Comparator

Linear Technology 

LTC1040

APPLICATIO S I FOR ATIO

Offset Voltage Error

The errors due to offset, common mode, power supply

variation, gain and temperature are all included in the

offset voltage specification. This makes it easy to compute

the error when using the LTC1040.

Example: error computation for Figure 4.

Assume: 2.8V ≤ VS ≤ 6V.

Then total worst-case error is:

IL

(ERROR)

=

±

(100mV

•

0.001

+

0.5mV)

•

1A

100mV

=

±

6mA

↑

↑

Tracking Error VOS

IL (ERROR)% =61mAA • 100 = ± 0.6%.

Note: If source resistance exceeds 10k, bypass

capacitors should be used and the associated errors must

be included.

The VP-P output voltage is not precise (see VP-P Output

Voltage versus Load Current curve). There are two ways

VP-P can be used to power external networks without

excessive errors: (1) ratiometric networks and (2) fast

settling references.

In a ratiometric network, the inputs are all proportional to

VP-P (see Figure 6). Consequently, for small changes, the

absolute value of VP-P does not affect accuracy.

It is critical that the inputs to the LTC1040 completely

settle within 4µs of the start of the comparison cycle and

that they do not change during the 80µs ON time. When

driving resistive networks with VP-P, capacitive loading on

VP-P OUTPUT

– VIN +

VTRIP

+

– 1/2

+ LTC1040

–

OUTPUT

Pulsed Power (VP-P) Output

It is often desirable to use comparators with resistive

networks such as bridges. Because of the extremely low

power consumption of the LTC1040, the power consumed

by these resistive networks can far exceed that of the

device itself.

At low sample rates the LTC1040 spends most of its time

off. To take advantage of this, a pulsed power (VP-P) output

is provided. VP-P is switched to V+ when the comparator

is on and to a high impedance (open circuit) when the

comparator is off. The ON time is nominally 80µs.

Figure 5 shows the VP-P output circuit.

V+

18

LTC1040 • AI06

Figure 6. Ratiometric Network Driven by VP-P

the network should be minimized to meet the 4µs settling

time requirement. It is not recommended that VP-P be used

to drive networks with source impedances, as seen by the

inputs, of greater than 10kΩ.

In applications where an absolute reference is required,

the VP-P output can be used to drive a fast settling

reference. The LT1009 2.5V reference, ideal in this

application, settles in approximately 2µs (see Figure 7).

The current through R1 must be large enough to supply

the LT1009 minimum bias current (≈1mA) and the load

current, IL.

VP-P OUTPUT

Q1 P1

80µs

COMPARATOR ON TIME

9

17

GND

VP-P

LTC1040 • AI05

Figure 5. VP-P Output Switch

R1

VIN

R2

LT1009 IL R3

+

– 1/2

+ LTC1040

–

LTC1040 • AI07

Figure 7. Driving Reference with VP-P Output

1040fa

7

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