OPA320 Datasheet, PDF (16/37 Pages) Texas Instruments – Precision, 20MHz, 0.9pA, Low-Noise, RRIO, CMOS Operational Amplifier with Shutdown

OPA320, OPA2320
OPA320S, OPA2320S
SBOS513E – AUGUST 2010 – REVISED JUNE 2013
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 (V–).
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.
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The key elements to a transimpedance design, as
shown in Figure 40, are the expected diode
capacitance (C_D), which should include the parasitic
input common-mode and differential-mode input
capacitance (4pF + 5pF for the OPA320); the desired
transimpedance gain (R_F); and the gain-bandwidth
(GBW) for the OPA320 (20MHz). With these three
variables set, the feedback capacitor value (C_F) can
be set to control the frequency response. C_F includes
the stray capacitance of R_F, which is 0.2pF for a
typical surface-mount resistor.
(1)
C_F
< 1pF
R_F
10MW
V+
l
C_D
OPA320
V_OUT
V-
(1) C_F is optional to prevent gain peaking. It includes the stray
capacitance of R_F.
Figure 40. Dual-Supply Transimpedance
Amplifier
To achieve a maximally-flat, second-order
Butterworth frequency response, the feedback pole
should be set to:
1
=
GBW
2pR_FC_F
4pR_FC_D
(1)
Bandwidth is calculated by:
f_-3dB =
GBW
2pR_FC_D
(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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