OPA320 Datasheet, PDF(15/31 Page) Texas Instruments – Precision, 20MHz, 0.9pA, Low-Noise, RRIO, CMOS Operational Amplifier with Shutdown

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OPA320 Datasheet, PDF (15/31 Pages) Texas Instruments – Precision, 20MHz, 0.9pA, Low-Noise, RRIO, CMOS Operational Amplifier with Shutdown

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GENERAL LAYOUT GUIDELINES

The OPA320 is a wideband amplifier. To realize the

full operational performance of the device, good

high-frequency printed circuit board (PCB) layout

practices are required. The bypass capacitors must

be connected between each supply pin and ground

as close to the device as possible. The bypass

capacitor traces should be designed for minimum

inductance.

LEADLESS DFN PACKAGE

The OPA320 series uses the DFN style package

(also known as SON), which is a QFN with contacts

on only two sides of the package bottom. This

leadless package maximizes PCB space and offers

enhanced thermal and electrical characteristics

through an exposed pad. One of the primary

advantages of the DFN package is its low height

(0.8mm).

DFN packages are physically small, have a smaller

routing area, improved thermal performance, reduced

electrical parasitics, and a pinout scheme that is

consistent with other commonly-used packages (such

as SO and MSOP). Additionally, the absence of

external leads eliminates bent-lead issues.

The DFN package can easily be mounted using

standard PCB assembly techniques. See Application

Report, QFN/SON PCB Attachment (SLUA271) and

Application Report, Quad Flatpack No-Lead Logic

Packages (SCBA017), both available for download at

www.ti.com. The exposed leadframe die pad on the

bottom of the DFN package should be connected

to the most negative potential (Vâ).

APPLICATION EXAMPLES

TRANSIMPEDANCE AMPLIFIER

Wide gain bandwidth, low input bias current, low input

voltage, and current noise make the OPA320 an ideal

wideband photodiode transimpedance amplifier.

Low-voltage noise is important because photodiode

capacitance causes the effective noise gain of the

circuit to increase at high frequency.

OPA320, OPA2320

OPA320S, OPA2320S

SBOS513D â AUGUST 2010 â REVISED NOVEMBER 2011

The key elements to a transimpedance design, as

shown in Figure 36, are the expected diode

capacitance (CD), which should include the parasitic

input common-mode and differential-mode input

capacitance (4pF + 5pF for the OPA320); the desired

transimpedance gain (RF); and the gain-bandwidth

(GBW) for the OPA320 (20MHz). With these three

variables set, the feedback capacitor value (CF) can

be set to control the frequency response. CF includes

the stray capacitance of RF, which is 0.2pF for a

typical surface-mount resistor.

(1)

< 1pF

10MW

V+

OPA320

VOUT

V-

(1) CF is optional to prevent gain peaking. It includes the stray

capacitance of RF.

Figure 36. Dual-Supply Transimpedance

Amplifier

To achieve a maximally-flat, second-order

Butterworth frequency response, the feedback pole

should be set to:

GBW

2pRFCF

4pRFCD

(1)

Bandwidth is calculated by:

f-3dB =

GBW

2pRFCD

(Hz)

(2)

For even higher transimpedance bandwidth, consider

the high-speed CMOS OPA380 (90MHz GBW),

OPA354 (100MHz GBW), OPA300 (180MHz GBW),

OPA355 (200MHz GBW), or OPA656/57 (400MHz

GBW).

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Product Folder Link(s): OPA320 OPA2320 OPA320S OPA2320S

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