Datasheet

f
-3dB
=
2 R Cp
F D
GBW
(Hz)
2 R Cp
F F
1
4 R Cp
F D
GBW
=
OPA320
V
OUT
V+
V-
C
D
R
10MW
F
C
<1pF
F
(1)
l
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 in Figure 40, are the expected diode
The OPA320 is a wideband amplifier. To realize the
capacitance (C
D
), 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 be
transimpedance gain (R
F
); 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 (C
F
) can
traces should be designed for minimum inductance.
be set to control the frequency response. C
F
includes
the stray capacitance of R
F
, 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) C
F
is optional to prevent gain peaking. It includes the stray
capacitance of R
F
.
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
To achieve a 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 is 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).
16 Submit Documentation Feedback Copyright © 2010–2013, Texas Instruments Incorporated
Product Folder Links: OPA320 OPA2320 OPA320S OPA2320S