LM4670SDX/NOPB National Semiconductor, LM4670SDX/NOPB Datasheet - Page 11

• Manufacturer Part Number: LM4670SDX/NOPB
• Description: IC AMP AUDIO PWR 3W MONO D 8LLP
• Manufacturer: National Semiconductor
• Series: Boomer®r
• Type: Class Dr

Specifications of LM4670SDX/NOPB

• Output Type: 1-Channel (Mono)
• Max Output Power X Channels @ Load: 3W x 1 @ 4 Ohm
• Voltage - Supply: 2.4 V ~ 5.5 V
• Features: Depop, Differential Inputs, Short-Circuit Protection, Shutdown
• Mounting Type: Surface Mount
• Package / Case: 8-LLP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: LM4670SDX

Application Information
current usage while in the shutdown state. While the
LM4670 may be disabled with shutdown voltages in between
ground and supply, the idle current will be greater than the
typical 0.01µA value. Increased THD may also be observed
with voltages less than V
PLAY mode.
The LM4670 has an internal resistor connected between
GND and Shutdown pins. The purpose of this resistor is to
eliminate any unwanted state changes when the Shutdown
pin is floating. The LM4670 will enter the shutdown state
when the Shutdown pin is left floating or if not floating, when
the shutdown voltage has crossed the threshold. To mini-
mize the supply current while in the shutdown state, the
Shutdown pin should be driven to GND or left floating. If the
Shutdown pin is not driven to GND, the amount of additional
resistor current due to the internal shutdown resistor can be
found by Equation (1) below.
With only a 0.5V difference, an additional 1.7µA of current
will be drawn while in the shutdown state.
PROPER SELECTION OF EXTERNAL COMPONENTS
The gain of the LM4670 is set by the external resistors, Ri in
Figure 1, The Gain is given by Equation (2) below. Best
THD+N performance is achieved with a gain of 2V/V (6dB).
It is recommended that resistors with 1% tolerance or better
be used to set the gain of the LM4670. The Ri resistors
should be placed close to the input pins of the LM4670.
Keeping the input traces close to each other and of the same
length in a high noise environment will aid in noise rejection
due to the good CMRR of the LM4670. Noise coupled onto
input traces which are physically close to each other will be
common mode and easily rejected by the LM4670.
Input capacitors may be needed for some applications or
when the source is single-ended (see Figures 3, 5). Input
capacitors are needed to block any DC voltage at the source
so that the DC voltage seen between the input terminals of
the LM4670 is 0V. Input capacitors create a high-pass filter
with the input resistors, R
filter is found using Equation (3) below.
The input capacitors may also be used to remove low audio
frequencies. Small speakers cannot reproduce low bass
frequencies so filtering may be desired . When the LM4670
is using a single-ended source, power supply noise on the
ground is seen as an input signal by the +IN input pin that is
A
V
f
(V
C
= 2 * 150 kΩ / R
SD
= 1 / (2πR
- GND) / 300kΩ
i
DD
. The –3dB point of the high-pass
on the Shutdown pin when in
i
C
i
) (Hz)
i
(V/V)
(Continued)
(1)
(2)
(3)
11
capacitor coupled to ground (See Figures 5 – 7). Setting the
high-pass filter point above the power supply noise frequen-
cies, 217Hz in a GSM phone, for example, will filter out this
noise so it is not amplified and heard on the output. Capaci-
tors with a tolerance of 10% or better are recommended for
impedance matching.
DIFFERENTIAL CIRCUIT CONFIGURATIONS
The LM4670 can be used in many different circuit configu-
rations. The simplest and best performing is the DC coupled,
differential input configuration shown in Figure 2. Equation
(2) above is used to determine the value of the R
for a desired gain.
Input capacitors can be used in a differential configuration as
shown in Figure 3. Equation (3) above is used to determine
the value of the C
sponse due to the high-pass filter created by C
Equation (2) above is used to determine the value of the R
resistors for a desired gain
The LM4670 can be used to amplify more than one audio
source. Figure 4 shows a dual differential input configuration.
The gain for each input can be independently set for maxi-
mum design flexibility using the R
and Equation (2). Input capacitors can be used with one or
more sources as well to have different frequency responses
depending on the source or if a DC voltage needs to be
blocked from a source.
SINGLE-ENDED CIRCUIT CONFIGURATIONS
The LM4670 can also be used with single-ended sources but
input capacitors will be needed to block any DC at the input
terminals. Figure 5 shows the typical single-ended applica-
tion configuration. The equations for Gain, Equation (2), and
frequency response, Equation (3), hold for the single-ended
configuration as shown in Figure 5.
When using more than one single-ended source as shown in
Figure 6, the impedance seen from each input terminal
should be equal. To find the correct values for C
connected to the +IN input pin the equivalent impedance of
all the single-ended sources are calculated. The single-
ended sources are in parallel to each other. The equivalent
capacitor and resistor, C
the parallel combination of all C
ues. Equations (4) and (5) below are for any number of
single-ended sources.
The LM4670 may also use a combination of single-ended
and differential sources. A typical application with one single-
ended source and one differential source is shown in Figure
7. Using the principle of superposition, the external compo-
nent values can be determined with the above equations
corresponding to the configuration.
R
i3
= 1 / (1/R
C
i3
i
= C
capacitors for a desired frequency re-
i1
i3
i1
+ C
and R
+ 1/R
i2
+ C
i2
i
i3
values and then all R
, are found by calculating
+ 1/R
i
in
resistors for each input
... (F)
in
...) (Ω)
www.national.com
i3
i
i
resistors
and R
and R
i
val-
(4)
(5)
i3
i
.
i