MAX44281 datasheet(8/10 Pages) MAXIM

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Maxim Integrated

MAX44281

Ultra-Small, Ultra-Thin, 4-Bump Op Amp

Detailed Description

Rail-to-Rail Output Stage

The MAX44281 is a high-bandwidth, low-power op

amp in the smallest 4-bump WLP industry package.

Its combination of precision, low-noise, and low-power

specifications makes it ideal for use in a wide variety of

sensor interface applications in portable consumer and

medical equipment.

Shutdown Mode

The MAX44281 features shutdown functionality by pulling

VDD to ground. During shutdown, both the input and

the output are high-impedance. The input and output of

the MAX44281 enter a high-impedance state when the

device enters shutdown. Since shutdown is triggered

by lowering the supply voltage to below 0.5V, the ESD

protection diodes at the output limit the high-Z voltage

range of the output. Diode D2 in Figure 2, from the output

of the amplifier to VDD, is forward biased when the output

voltage becomes too high in shutdown mode. The diodes

combined with the low-voltage shutdown functionality

effectively limit the high-impedance output range to plus

and minus a diode voltage around ground (~P 0.6V).

Driving Capacitive Loads

Driving a capacitive load can cause instability in many

op amps, especially those with low quiescent current.

The MAX44281 is stable for a range of capacitive loads

to above 400pF. Adding a series resistor between the

output and the load capacitor improves the circuit’s

response by isolating the load capacitance from the

op amp’s output. See the Isolation Resistance vs.

Capacitive-Load Stability graph in the Typical Operating

Characteristics section for details.

Applications Information

The MAX44281 features low input voltage offset and low

bias current, which makes the device ideal for single-

supply DC operations. However, its wide bandwidth and

low noise make it suitable also for AC applications. The

circuit in Figure 1 enables AC-coupled applications with

the simple addition of two external resistors R1 and R2.

Such resistors set the output bias voltage at midsupply.

The values of R1 and R2 depend on the gain option of the

device, according to the equation:

VDD x (R2/(R1 + R2)) = VDD/(2 x AV)

Driver for Interfacing with

the MAX11645 ADC

The MAX44281’s tiny size and low noise make it a

good fit for driving 12- to 16-bit resolution ADCs in

space-constrained applications. The Typical Application

Circuit shows the MAX44281 amplifier output connected

to a lowpass filter driving the MAX11645 ADC. The

MAX11645 is part of a family of 3V and 5V, 12-bit and

10-bit, 2-channel ADCs.

The MAX11645 offers sample rates up to 94ksps and

measures two single-ended inputs or one differential

input. These ADCs dissipate 670FA at the maximum

sampling rate, but just 6FA at 1ksps and 0.5FA in shut-

down. Offered in the ultra-tiny, 1.9mm x 2.2mm WLP

and FMAX-8 packages, the MAX11645 ADCs are an

ideal fit to pair with the MAX44281 amplifier in portable

applications.

Where higher resolution is required, refer to the MAX1069

(14-bit) and MAX1169 (16-bit) ADC families.

Figure 1. How to Use the MAX44281 in AC-Coupled

Applications

Figure 2. Output ESD Protection Diodes

VDD

OUT

GND

OUT

VOUT

VDD

VIN

VDD

GND

MAX44281

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