低功耗微功率运算放大器NCS2009-D：小巧高效设计

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NCS2009-D芯片研究手册主要关注的是MicroPower系列的低成本运算放大器，特别是OPA347型号。这款单片机芯片以其微型包装设计为特点，包括SC-70、SOT23-5、SOT23-8、WCSP-8以及TSSOP-14等封装选项，满足了不同应用场合对尺寸和集成度的需求。对于单通道版本的OPA347，其最大功耗低至34微安，这使得它在便携式设备和电池供电设备中具有极高的能源效率。 OPA347的关键特性包括： 1. **超低功耗**：20微安级别的GLOWIQ电流消耗，对于电池供电设备来说尤其重要，延长了电池寿命。 2. **微型化封装**：如WCSP-8、SC70-5和SOT23系列，提供紧凑的解决方案，便于集成到小型电路板上。 3. **高带宽**：高达350千赫兹的 bandwidth，保证了快速信号处理能力，适合对速度有较高要求的应用。 4. **轨至轨输入和输出**：输入范围超过电源电压200毫伏，输出范围接近电源电压，确保了宽广的动态范围。 5. **单电源工作**：工作电压范围从2.3V到5.5V，兼容性广泛，无需外部电源转换。在应用方面，OPA347非常适合： - **便携设备**：其低功耗特性使其成为移动设备的理想选择，如手机、平板等。 - **电池供电设备**：由于其节能特性，适用于电池续航时间至关重要的设备。 - **2线传输器**：由于高速性能，它可以用于需要高效数据传输的系统。 - **烟雾检测器**：可能需要高灵敏度和低功耗的环境监测设备。 - **传感器应用**：代码检测器或其他需要放大和处理信号的场合。 NCS2009-D芯片研究手册中的OPA347是一款高度集成、低功耗且性能优越的运算放大器，特别适合于对小型化、功耗敏感和速度要求高的电子设备设计。通过了解其特性和应用领域，工程师们可以更有效地利用这款芯片来提升产品的性能和能源效率。

OPA347, 2347, 4347

SBOS167D

www.ti.com

APPLICATIONS INFORMATION

The OPA347 series op amps are unity-gain stable and can

operate on a single supply, making them highly versatile and

easy to use.

Rail-to-rail input and output swing significantly increases dy-

namic range, especially in low supply applications. Figure 1

shows the input and output waveforms for the OPA347 in

unity-gain configuration. Operation is from V

= +5V with a

100kΩ load connected to V

/2. The input is a 5V

sinusoid.

Output voltage is approximately 4.995V

Power-supply pins should be bypassed with 0.01µF ceramic

capacitors.

OPERATING VOLTAGE

The OPA347 series op amps are fully specified and en-

sured from 2.5V to 5.5V. In addition, many specifications

apply from –55°C to +125°C. Parameters that vary signifi-

cantly with operating voltages or temperature are shown in

the Typical Characteristics.

RAIL-TO-RAIL INPUT

The input common-mode voltage range of the OPA347

series extends 200mV beyond the supply rails. This is

achieved with a complementary input stage—an N-channel

input differential pair in parallel with a P-channel differential

pair, as shown in Figure 2. The N-channel pair is active for

input voltages close to the positive rail, typically (V+) – 1.3V

to 200mV above the positive supply, while the P-channel pair

is on for inputs from 200mV below the negative supply to

approximately (V+) – 1.3V. There is a small transition region,

typically (V+) – 1.5V to (V+) – 1.1V, in which both pairs are

on. This 400mV transition region can vary 300mV with

process variation. Thus, the transition region (both stages

on) can range from (V+) – 1.65V to (V+) – 1.25V on the low

end, up to (V+) – 1.35V to (V+) – 0.95V on the high end.

Within the 400mV transition region PSRR, CMRR, offset

voltage, and offset drift may be degraded compared to

operation outside this region. For more information on de-

signing with rail-to-rail input op amps, see Figure 3,

Design

Optimization with Rail-to-Rail Input Op Amps

FIGURE 2. Simplified Schematic.

FIGURE 1. Rail-to-Rail Input and Output.

BIAS1

BIAS2

–

Class AB

Control

Circuitry

V–

(Ground)

V+

Reference

Current

Input

Output (inverted on scope)

1V/div

G = +1, V

= +5V

20µs/div

OPA347, 2347, 4347

SBOS167D

www.ti.com

COMMON-MODE REJECTION

The CMRR for the OPA347 is specified in several ways so

the best match for a given application may be used. First, the

CMRR of the device in the common-mode range below the

transition region (V

< (V+) – 1.7V) is given. This specifica-

tion is the best indicator of the capability of the device when

the application requires use of one of the differential input

pairs. Second, the CMRR at V

= 5.5V over the entire

common-mode range is specified.

INPUT VOLTAGE

The input common-mode range extends from (V–) – 0.2V to

(V+) + 0.2V. For normal operation, inputs should be limited

to this range. The absolute maximum input voltage is 500mV

beyond the supplies. Inputs greater than the input

common-mode range but less than the maximum input

voltage, while not valid, will not cause any damage to the op

amp. Furthermore, if input current is limited the inputs may go

beyond the power supplies without phase inversion, as

shown in Figure 4, unlike some other op amps.

Normally, input currents are 0.4pA. However, large inputs

(greater than 500mV beyond the supply rails) can cause

excessive current to flow in or out of the input pins. There-

fore, as well as keeping the input voltage below the maxi-

mum rating, it is also important to limit the input current to

less than 10mA. This is easily accomplished with an input

resistor, as shown in Figure 5.

FIGURE 3. Design Optimization with Rail-to-Rail Input Op Amps.

Rail-to-rail op amps can be used in virtually any op amp

configuration. To achieve optimum performance, how-

ever, applications using these special double-input-stage

op amps may benefit from consideration of their special

behavior.

In many applications, operation remains within the com-

mon-mode range of only one differential input pair. How-

ever, some applications exercise the amplifier through the

transition region of both differential input stages. A small

discontinuity may occur in this transition. Careful selection

of the circuit configuration, signal levels, and biasing can

often avoid this transition region.

DESIGN OPTIMIZATION WITH RAIL-TO-RAIL INPUT OP AMPS

With a unity-gain buffer, for example, signals will traverse

this transition at approximately 1.3V below the V+ supply

and may exhibit a small discontinuity at this point.

The common-mode voltage of the noninverting amplifier

is equal to the input voltage. If the input signal always

remains less than the transition voltage, no discontinuity

will be created. The closed-loop gain of this configuration

can still produce a rail-to-rail output.

Inverting amplifiers have a constant common-mode volt-

age equal to V

. If this bias voltage is constant, no

discontinuity will be created. The bias voltage can gener-

ally be chosen to avoid the transition region.

FIGURE 4. OPA347—No Phase Inversion with Inputs Greater

than the Power-Supply Voltage.

V+

Noninverting Amplifier

= V

V+

Inverting Amplifier

= V

V+

Unity-Gain Buffer

= V

FIGURE 5. Input Current Protection for Voltages Exceeding

the Supply Voltage.

5kΩ

OPA347

10mA max

+5V

OUT

OVERLOAD

5.5V

–0.5V

200µs/div

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