LM4675TLBD National Semiconductor, LM4675TLBD Datasheet - Page 13

• Manufacturer Part Number: LM4675TLBD
• Description: BOARD EVALUATION LM4675TL
• Manufacturer: National Semiconductor
• Series: Boomer®, PowerWise®r

Specifications of LM4675TLBD

• Amplifier Type: Class D
• Output Type: 1-Channel (Mono)
• Max Output Power X Channels @ Load: 2.7W x 1 @ 4 Ohm
• Voltage - Supply: 2.4 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Board Type: Fully Populated
• Utilized Ic / Part: LM4675
• Lead Free Status / RoHS Status: Not applicable / Not applicable

usage while in the shutdown state. While the LM4675 may be
disabled with shutdown voltages in between ground and sup-
ply, the idle current will be greater than the typical 0.01µA
value.
The LM4675 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 LM4675 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 minimize 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 Equa-
tion (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 LM4675 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 LM4675. The Ri resistors should
be placed close to the input pins of the LM4675. 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 LM4675. Noise coupled onto input traces
which are physically close to each other will be common mode
and easily rejected by the LM4675.
Input capacitors may be needed for some applications or
when the source is single-ended (see Figures 3, 5). Input ca-
pacitors are needed to block any DC voltage at the source so
that the DC voltage seen between the input terminals of the
LM4675 is 0V. Input capacitors create a high-pass filter with
the input resistors, R
is found using Equation (3) below.
The input capacitors may also be used to remove low audio
frequencies. Small speakers cannot reproduce low bass fre-
quencies so filtering may be desired . When the LM4675 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
capacitor coupled to ground (See Figures 5 – 7). Setting the
A
V
f
C
= 2 * 150 kΩ / R
(V
= 1 / (2
SD
i
. The –3dB point of the high-pass filter
- GND) / 300kΩ
π
R
i
C
i
)
i
(Hz)
(V/V)
(1)
(2)
(3)
13
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. Capacitors
with a tolerance of 10% or better are recommended for
impedance matching.
DIFFERENTIAL CIRCUIT CONFIGURATIONS
The LM4675 can be used in many different circuit configura-
tions. 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
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 LM4675 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
Equation (2). Input capacitors can be used with one or more
sources as well to have different frequency responses de-
pending on the source or if a DC voltage needs to be blocked
from a source.
SINGLE-ENDED CIRCUIT CONFIGURATIONS
The LM4675 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 application
configuration. The equations for Gain, Equation (2), and fre-
quency 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
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 resis-
tor, C
nation of all C
(5) below are for any number of single-ended sources.
The LM4675 may also use a combination of single-ended and
differential sources. A typical application with one single-end-
ed source and one differential source is shown in Figure 7.
Using the principle of superposition, the external component
values can be determined with the above equations corre-
sponding to the configuration.
i3
and R
R
i3
= 1 / (1/R
i
i3
values and then all R
C
, are found by calculating the parallel combi-
i3
= C
i
capacitors for a desired frequency re-
i1
i1
+ C
+ 1/R
i2
+ C
i2
+ 1/R
i
in
resistors for each input and
i
values. Equations (4) and
(F)
in
) (Ω)
i3
and R
i
resistors for a
i3
www.national.com
connected
i
and R
(4)
(5)
i
.
i