Specifications

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Compensation www.ti.com
One of the features of the LME49830 is the ability to set the amplifier’s slew rate and power bandwidth
through the selection of the external compensation capacitor value. Lowering the value of the
compensation capacitor increases the amplifier’s slew rate and hence its power bandwidth.
Slew Rate = ΔV/Δt = 2πf
MAX
V
Opk
(14)
The amplifier’s power bandwidth is also determined through this equation and can be related to the
amplifier’s slew rate as shown below.
f
PBW
= Slew Rate/2πV
Opk
(15)
The power bandwidth equation indicates that higher output power amplifiers will require larger slew rates
to maintain a constant power bandwidth. Shown in Table 6 are the required amplifier slew rates for a
100kHz power bandwidth for different output power levels.
Table 6. Slew Rates For 100kHz Power Bandwidth
Output Power (W) Slew Rate (μs)
V
O(PEAK)
(V)
(R
L
= 8Ω) (f
BW
= 100kHz)
125 44.7 28
250 63.2 40
500 89.4 56
The maximum slew rate for an amplifier will be dependent upon the value of the compensation capacitor,
in conjunction with the maximum tail current of the input differential transistor pair.
Slew Rate = dV/dt = I
MAX
/ C
COMP
(16)
The LME49830 has a maximum input differential pair tail current of 550µA, so corresponding slew rates
for compensation capacitor values are shown in Table 7.
Table 7. LME49830 Slew Rate vs Compensation Capacitor
Compensation Slew Rate
Capacitor, C
COMP
(pF) (V/µs)
5 110
10 55
12 46
15 37
18 31
20 27
25 22
30 19
60 9
100 5.5
Since slew rate requirements are different depending upon desired power bandwidth and output power
level, we can calculate the needed compensation capacitor for a given design based on the equation
below.
(17)
Shown in Table 8 are appropriate compensation capacitor values for 100kHz power bandwidths at the
stated amplifier output power levels.
Table 8. Compensation Capacitor Required Per Reference Design
Reference Design (8Ω) Compensation Capacitor, C
COMP
(pF) Slew Rate (V/µs) Power Bandwidth (kHz)
125W 20 28 100
250W 12 40 100
450W 10 53 100
20
AN-1850 LME49830TB Ultra-High Fidelity High-Power Amplifier Reference SNAA058B–July 2008–Revised May 2013
Design
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