December 4, 2008
LMH730227/LMH730216/LMH730165
Single High Speed Op Amp Evaluation Boards (SOIC,
SOT-23, and SC-70)
The LMH730227, LMH730216 and LMH730165 evaluation
boards are designed to aid in the characterization of National
Semiconductor's High Speed monolithic amplifiers.
•LMH730227 — SOIC packages
•LMH730216 — SOT-23 packages
•LMH730165 — SC-70 packges
Use the evaluation boards as a guide for high frequency lay-
out and as a tool to aid in device testing and characterization.
The evaluation boards accommodate general purpose am-
plifiers, as well as amplifiers with the following features:
•Supply current adjustment via external Resistor
•Output disable
The evaluation board schematic is shown below. Refer to the
product data sheets for recommendations for component val-
ues.
BASIC OPERATION
These boards have identical circuit configurations and are
designed to accommodate both non-inverting and inverting
operation. By changing RT or RIN and ROUT different input
and output impedances can be matched. The SMA connec-
tors and board traces are optimized for 50Ω operation, how-
ever other impedances can be matched as shown below.
Inverting Gain = RF/RG (Input Resistance = RT || RG)
Non Inverting Gain = 1 + RF/(RG + RT)
(Input Resistance = RIN)
(RT may be set to zero for non inverting operation)
For current feedback operational amplifiers be careful to use
appropriate values of RF. In addition the required value of
RG will limit choices for input impedance with Inverting gains.
20066601
FIGURE 1. SOT-23 and SC-70 Schematic
© 2008 National Semiconductor Corporation 200666 www.national.com
LMH730227/LMH730216/ LMH730165 Single High Speed Op Amp Evaluation Boards (SOIC,
SOT-23 and SC-70)
LAYOUT CONSIDERATIONS
Printed circuit board layout and supply bypassing play major
roles in determining high frequency performance. When de-
signing your own board use these evaluation boards as a
guide and follow these steps to optimize high frequency per-
formance:
20066602
FIGURE 2. SOIC Schematic
20066603
FIGURE 3. Probe Schematic
www.national.com 2
LMH730227,LMH730216
1. Use a ground plane
2. Include large (~6.8μF) capacitors on both supplies.
3. Near the device use .01μF ceramic capacitors from both
supplies to ground C1, C3.
4. Near the device use a .1μF ceramic capacitor between
the supplies C5.
5. Remove the ground and power planes from under and
around the part, especially the input and output pins.
6. Minimize all trace lengths.
7. Use terminated transmission lines for long traces.
8. High-speed disable/enable operation requires that the
enable pin be treated as a signal input.
Diode D1 is to protect the device from reverse polarity supply
connections and will not be necessary for most designs.
Capacitor C5 is necessary for best Harmonic Distortion per-
formance. If C5 is not used increase the values of C1 and C3
to .1μF.
RIN, RT and ROUT are all impedance matching resistors. RIN
and ROUT should be equal to the desired input/output
impedance. RT || RG should equal the desired inverting input
impedance. Note that with current feedback op amps, the op-
timum value of RF and RG is determined by the desired gain
and raising RG to obtain higher input impedance may require
compromising device performance at large values of inverting
gain.
The disable trace has provisions for input termination. There
are also pads for series resistance and capacitance for pro-
grammable gain parts. See part datasheets for suggested
values.
Sample artwork for National's Evaluation boards is included
below.
The board is designed for 50Ω input and output connections
into coaxial cables. For other impedances the terminating re-
sistors can be modified to help match different impedances.
Do not use normal oscilloscope probes to test these circuits.
The capacitive loading will change circuit performance dras-
tically. Instead use low impedance resistive divider probes of
100 to 500Ω. See Figure 3 for a sample resistive probe. The
Low impedance resistor should be 50-450Ω. The ground con-
nection should be as short as possible (~1/2"). Even with
careful use of these probes results should be considered pre-
liminary until verified with controlled impedance measure-
ments. Even the best probes will interfere with circuit
operation to some degree. Also, conductors, fingers etc. near
the device will change measurement results.
National Semiconductor Layer1 Silk
20066604
National Semiconductor Layer2 Silk
20066605
SOIC Board Layout (Actual size = 1.5" x 1.5"). The boards may be marked as CLC730227 or LMH730227
3 www.national.com
LMH730227,LMH730216
National Semiconductor Layer2 Silk
20066610
National Semiconductor Layer1 Silk
20066611
SOT-23 Board Layout (Actual size = 1.5" x 1.5").
National Semiconductor Layer1 Silk
20066608
National Semiconductor Layer2 Silk
20066609
SC-70 Board Layout (Actual size = 1.5" x 1.5")
www.national.com 4
LMH730227,LMH730216
5 www.national.com
LMH730227,LMH730216
Notes
LMH730227/LMH730216/ LMH730165 Single High Speed Op Amp Evaluation Boards (SOIC,
SOT-23 and SC-70)
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