Datasheet

LM7372
www.ti.com SNOS926E –MAY 1999–REVISED MARCH 2013
P
D(TOTAL)
= P
Q
+ P
DC
+ P
AC
P
Q
= |I
S
• V
S
| Op Amp Quiescent Power Dissipation
P
DC
= |I
O
• (V
R
- V
O
)| DC Load Power
P
AC
= See Table 3 AC Load Power
where:
I
S
Supply Current
V
S
Total Supply Voltage (V
+
- V
−
)
I
O
Average Load Current
V
O
Average Output Voltage
V
R
Reference Voltage (V
+
for sourcing and V
−
for sinking current)
Table 3 below shows the maximum AC component of the load power dissipated by the op amp for standard
Sinusoidal, Triangular, and Square Waveforms:
Table 3. Normalized maximum AC Power Dissipated in the Output Stage for Standard Waveforms
P
AC
(W.Ω/V
2
)
Sinusoidal Triangular Square
50.7 x 10
−3
46.9 x 10
−3
62.5 x 10
−3
The table entries are normalized to V
S
2
/R
L
. These entries are computed at the output swing point where the
amplifier dissipation is the highest for each waveform type. To figure out the AC load current component of
power dissipation, simply multiply the table entry corresponding to the output waveform by the factor V
S
2
/R
L
. For
example, with ±5V supplies, a 100Ω load and triangular output waveform, power dissipation in the output stage is
calculated as: P
AC
= 46.9 x 10
−3
x 10
2
/100 = 46.9mW which contributes another 2.2°C (= 46.9mW x 47°C/W) rise
to the LM7372 junction temperature in the 8-Pin SO PowerPAD package.
POWER SUPPLIES
The LM7372 is fabricated on a high voltage, high speed process. Using high supply voltages ensures adequate
headroom to give low distortion with large signal swings. In Figure 1, a single 24V supply is used. To maximize
the output dynamic range the non-inverting inputs are biased to half supply voltage by the resistive divider R1,
R2. The input signals are AC coupled and the coupling capacitors (C1, C2) can be scaled with the bias resistors
(R3, R4) to form a high pass filter if unwanted coupling from the POTS signal occurs.
Supply decoupling is important at both low and high frequencies. The 10µF Tantalum and 0.1µF Ceramic
capacitors should be connected close to the supply Pin 14. Note that the V
−
pin (pin 6), and the PCB area
associated with the heatsink (Pins 1,8,9 & 16) are at the same potential. Any layout should avoid running input
signal leads close to this ground plane, or unwanted coupling of high frequency supply currents may generate
distortion products.
Although this application shows a single supply, conversion to a split supply is straightforward. The half supply
resistive divider network is eliminated and the bias resistors at the non-inverting inputs are returned to ground,
see Figure 28 (the pin numbers in Figure 28 are given for SO PowerPAD package, those in Figure 1 are for the
SOIC package). With a split supply, note that the ground plane and the heatsink copper must be separate and
are at different potentials, with the heatsink (pin 4 of the SO PowerPAD, pins 6,1,8,9 &16 of the SOIC) now at a
negative potential (V
−
).
In either configuration, the area under the input pins should be kept clear of copper (whether ground plane
copper or heatsink copper) to avoid parasitic coupling to the inputs.
The LM7372 is stable with non inverting closed loop gains as low as +2. Typical of any voltage feedback
operational amplifier, as the closed loop gain of the LM7372 is increased, there is a corresponding reduction in
the closed loop signal bandwidth. For low distortion performance it is recommended to keep the closed loop
bandwidth at least 10X the highest signal frequency. This is because there is less loop gain (the difference
between the open loop gain and the closed loop gain) available at higher frequencies to reduce harmonic
distortion terms.
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