AD8045ACPZ-R2 Analog Devices Inc, AD8045ACPZ-R2 Datasheet - Page 23

• Manufacturer Part Number: AD8045ACPZ-R2
• Description: IC OPAMP VF ULDIST LN 8LFCSP
• Manufacturer: Analog Devices Inc

Specifications of AD8045ACPZ-R2

• Slew Rate: 1350 V/µs
• Amplifier Type: Voltage Feedback
• Number Of Circuits: 1
• -3db Bandwidth: 1GHz
• Current - Input Bias: 2µA
• Voltage - Input Offset: 200µV
• Current - Supply: 16mA
• Current - Output / Channel: 70mA
• Voltage - Supply, Single/dual (±): 3.3 V ~ 12 V, ±1.65 V ~ 6 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-LFCSP
• Op Amp Type: Low Distortion
• No. Of Amplifiers: 1
• Bandwidth: 1MHz
• Supply Voltage Range: 3.3V To 12V
• Amplifier Case Style: LFCSP
• No. Of Pins: 8
• Operating Temperature Range: -40°C To
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Output Type: -
• Gain Bandwidth Product: -
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Lead free / RoHS Compliant

EXPOSED PADDLE
The AD8045 features an exposed paddle, which lowers the
thermal resistance by 25% compared to a standard SOIC plastic
package. The exposed paddle of the AD8045 is internally con-
nected to the negative power supply pin. Therefore, when laying
out the board, the exposed paddle must either be connected to
the negative power supply or left floating (electrically isolated).
Soldering the exposed paddle to the negative power supply metal
ensures maximum thermal transfer. Figure 74 and Figure 75 show
the proper layout for connecting the SOIC and LFCSP exposed
paddle to the negative supply.
The use of thermal vias or “heat pipes” can also be incorporated
into the design of the mounting pad for the exposed paddle.
These additional vias help to lower the overall theta junction to
ambient (θ
which the amplifier’s exposed paddle is soldered can greatly
reduce the overall thermal resistance “seen” by the AD8045.
For existing designs that want to incorporate the AD8045,
electrically isolating the exposed paddle is another option. If the
exposed paddle is electrically isolated, the thermal dissipation is
primarily through the leads, and the thermal resistance of the
package now approaches 125°C/W, the standard SOIC θ
However, a thermally conductive and electrically isolated pad
material may be used. A thermally conductive spacer, such as
the Bergquist Company’s Sil-Pad, is an excellent solution to this
problem. Figure 76 shows a typical implementation using
thermal pad material.
JA
). Using a heavier weight copper on the surface to
Figure 75. LFCSP Exposed Paddle Layout
Figure 74. SOIC Exposed Paddle Layout
JA
.
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The thermal pad provides high thermal conductivity but
isolates the exposed paddle from ground or other potential. It is
recommended, when possible, to solder the paddle to the nega-
tive power supply plane or trace for maximum thermal transfer.
Note that soldering the paddle to ground shorts the negative
power supply to ground and can cause irreparable damage to
the AD8045.
DRIVING CAPACITIVE LOADS
In general, high speed amplifiers have a difficult time driving
capacitive loads. This is particularly true in low closed-loop
gains, where the phase margin is the lowest. The difficulty arises
because the load capacitance, C
resistance, R
equation
If this pole occurs too close to the unity gain crossover point,
the phase margin degrades. This is due to the additional phase
loss associated with the pole.
The AD8045 output can drive 18 pF of load capacitance directly,
in a gain of +2 with 30% overshoot, as shown in Figure 37.
Larger capacitance values can be driven but must use a snub-
bing resistor (R
Figure 61 and Figure 62. Adding a small series resistor, R
creates a zero that cancels the pole introduced by the load
capacitance. Typical values for R
50 Ω. The value is typically arrived at empirically and based on
the circuit requirements.
f
P
=
Figure 76. SOIC with Thermal Conductive Pad Material
THERMAL CONDUCTIVE INSULATOR
2π
O
R
, of the amplifier. The pole can be described by the
1
O
SNUB
C
L
) at the output of the amplifier, as shown in
L
, forms a pole with the output
SNUB
can range from 25 Ω to
AD8045
SNUB
,