OPA320 datasheet(16/37 Pages) NSC

16 / 37 page

3dB =

2 R C

GBW

(Hz)

2 R C

4 R C

GBW

OPA320

OUT

V+

V-

10MW

<1pF

(1)

OPA320, OPA2320

OPA320S, OPA2320S

SBOS513E – AUGUST 2010 – REVISED JUNE 2013

www.ti.com

GENERAL LAYOUT GUIDELINES

The key elements to a transimpedance design, as

shown

Figure

40,

are

the

expected

diode

The OPA320 is a wideband amplifier. To realize the

capacitance (CD), which should include the parasitic

full operational performance of the device, good high-

input

common-mode

and

differential-mode

input

frequency printed circuit board (PCB) layout practices

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

are

required.

The

bypass

capacitors

must

transimpedance gain (RF); and the gain-bandwidth

connected between each supply pin and ground as

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

close to the device as possible. The bypass capacitor

variables set, the feedback capacitor value (CF) can

traces should be designed for minimum inductance.

be set to control the frequency response. CF includes

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

LEADLESS DFN PACKAGE

typical surface-mount resistor.

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.

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

capacitance of RF.

The DFN package can easily be mounted using

standard PCB assembly techniques. See Application

Figure 40. Dual-Supply Transimpedance

Report, QFN/SON PCB Attachment (SLUA271) and

Amplifier

Application Report, Quad Flatpack No-Lead Logic

Packages (SCBA017), both available for download at

achieve

maximally-flat,

second-order

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

Butterworth frequency response, the feedback pole

bottom of the DFN package should be connected

should be set to:

to the most negative potential (V–).

APPLICATION EXAMPLES

(1)

Bandwidth is calculated by:

TRANSIMPEDANCE AMPLIFIER

Wide gain bandwidth, low input bias current, low input

voltage, and current noise make the OPA320 an ideal

(2)

wideband photodiode transimpedance amplifier. Low-

voltage

noise

important

because

photodiode

For even higher transimpedance bandwidth, consider

capacitance causes the effective noise gain of the

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

circuit to increase at high frequency.

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

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

GBW).

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