MAX44248ASA 查看數據表（PDF） - Maxim Integrated

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MAX44248ASA

36V, Precision, Low-Power, 90µA, Single/Quad/Dual Op Amps

Maxim Integrated 

MAX44244/MAX44245/MAX44248

36V, Precision, Low-Power, 90µA,

Single/Quad/Dual Op Amps

circuit, both the DAC and the reference are referred to

the local ground. The MAX44244 op-amp inputs are

capable of swinging to the negative supply (which is the

local ground in this case). R3 acts as a current mirror with

RSENSE. Therefore, if RSENSE = 50Ω (i.e. 20mA will drop

1V) and if the current through R3 is 10μA when IOUT is

20mA (0.05% error) then R3 = 100kΩ. R1 is chosen along

with the reference voltage to provide the 4mA offset. R2

= 512kΩ for 20mA full scale or R2 = 614kΩ for 20% over-

range. RSENSE is ratiometric with R3, R1 independently

sets the offset current and R2 independently sets the

DAC scaling.

Driving High-Performance ADCs

The MAX44244/MAX44245/MAX44248’s low input offset

voltage and low noise make these amplifiers ideal for

ADC buffering. Weight scale applications require a low-

noise, precision amplifier in front of an ADC. Figure 1

details an example of a load cell and amplifier driven

from the same 5V supply, along with a 16-bit delta sigma

ADC such as the MAX11205.

The MAX11205 is an ultra-low-power (< 300FA, max

active current), high-resolution, serial output ADC. It

provides the highest resolution per unit power in the

industry and is optimized for applications that require

very high dynamic range with low power such as sensors

on a 4–20mA industrial control loop. The devices provide

a high-accuracy internal oscillator that requires no

external components.

Layout Guidelines

The MAX44244/MAX44245/MAX44248 feature ultra-low

input offset voltage and noise. Therefore, to get optimum

performance follow the layout guidelines.

Avoid temperature tradients at the junction of two

dissimilar metals. The most common dissimilar metals

used on a PCB are solder-to-component lead and

solder-to-board trace. Dissimilar metals create a local

thermocouple. A variation in temperature across the

board can cause an additional offset due to Seebeck

effect at the solder junctions. To minimize the Seebeck

effect, place the amplifier away from potential heat

sources on the board, if possible. Orient the resistors

such that both the ends are heated equally. It is a good

practice to match the input signal path to ensure that the

type and number of thermoelectric juntions remain the

same. For example, consider using dummy 0ω resistors

oriented in such a way that the thermoelectric source, due

to the real resistors in the signal path, are cancelled. It is

recommended to flood the PCB with ground plane. The

ground plane ensures that heat is distributed uniformly

reducing the potential offset voltage degradation due to

Seebeck effect.

5V

½ MAX44248

5V

AMP A

VDD

5V

RF

RG

RF

VDD

VIN+

MAX11205

OUTPUT

VIN-

VSS

MICRO

CONTROLLER

AMP B

½ MAX44248

Figure 1. Weight Application

Maxim Integrated

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