LM4936MHX/NOPB National Semiconductor, LM4936MHX/NOPB Datasheet - Page 19

• Manufacturer Part Number: LM4936MHX/NOPB
• Description: IC AMP AUDIO PWR 2.2W AB 28TSSOP
• Manufacturer: National Semiconductor
• Series: Boomer®r
• Type: Class ABr

Specifications of LM4936MHX/NOPB

• Output Type: 2-Channel (Stereo) with Stereo Headphones
• Max Output Power X Channels @ Load: 2.2W x 2 @ 3 Ohm; 110mW x 2 @ 32 Ohm
• Voltage - Supply: 2.7 V ~ 5.5 V
• Features: Bass Boost, Depop, I²C, Mute, Shutdown, SPI, Thermal Protection, Volume Control
• Mounting Type: Surface Mount
• Package / Case: 28-TSSOP Exposed Pad, 28-eTSSOP, 28-HTSSOP
• Operational Class: Class-AB
• Audio Amplifier Output Configuration: 2-Channel Stereo
• Audio Amplifier Function: Headphone/Speaker
• Total Harmonic Distortion: 0.06@8Ohm@0.4W%
• Single Supply Voltage (typ): 3/5V
• Dual Supply Voltage (typ): Not RequiredV
• Power Supply Requirement: Single
• Rail/rail I/o Type: No
• Power Supply Rejection Ratio: 57dB
• Single Supply Voltage (min): 2.7V
• Single Supply Voltage (max): 5.5V
• Dual Supply Voltage (min): Not RequiredV
• Dual Supply Voltage (max): Not RequiredV
• Operating Temp Range: -40C to 85C
• Operating Temperature Classification: Industrial
• Mounting: Surface Mount
• Pin Count: 28
• Package Type: TSSOP EP
• For Use With: LM4936MHEVAL - BOARD EVALUATION LM4936MH
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: LM4936MHX

Application Information
the length of leads and traces that connect capacitors be-
tween the LM4936’s power supply pin and ground as short
as possible. Connecting a 1µF capacitor, C
BYPASS pin and ground improves the internal bias voltage’s
stability and the amplifier’s PSRR. The PSRR improvements
increase as the BYPASS pin capacitor value increases. Too
large a capacitor, however, increases turn-on time and can
compromise the amplifier’s click and pop performance. The
selection of bypass capacitor values, especially C
on desired PSRR requirements, click and pop performance
(as explained in the following section, Selecting Proper
External Components), system cost, and size constraints.
SELECTING PROPER EXTERNAL COMPONENTS
Optimizing the LM4936’s performance requires properly se-
lecting external components. Though the LM4936 operates
well when using external components with wide tolerances,
best performance is achieved by optimizing component val-
ues.
The LM4936 is unity-gain stable, giving a designer maximum
design flexibility. The gain should be set to no more than a
given application requires. This allows the amplifier to
achieve minimum THD+N and maximum signal-to-noise ra-
tio. These parameters are compromised as the closed-loop
gain increases. However, low gain circuits demand input
signals with greater voltage swings to achieve maximum
output power. Fortunately, many signal sources such as
audio CODECs have outputs of 1V
refer to the Audio Power Amplifier Design section for more
information on selecting the proper gain.
INPUT CAPACITOR VALUE SELECTION
Amplifying the lowest audio frequencies requires a high
value input coupling capacitor (0.33µF in Figure 2), but high
value capacitors can be expensive and may compromise
space efficiency in portable designs. In many cases, how-
ever, the speakers used in portable systems, whether inter-
nal or external, have little ability to reproduce signals below
150 Hz. Applications using speakers with this limited fre-
quency response reap little improvement by using a large
input capacitor.
Besides affecting system cost and size, the input coupling
capacitor has an effect on the LM4936’s click and pop per-
formance. When the supply voltage is first applied, a tran-
sient (pop) is created as the charge on the input capacitor
changes from zero to a quiescent state. The magnitude of
the pop is directly proportional to the input capacitor’s size.
Higher value capacitors need more time to reach a quiescent
DC voltage (V
amplifier’s output charges the input capacitor through the
feedback resistor, R
lecting an input capacitor value that is no higher than nec-
essary to meet the desired −6dB frequency.
As shown in Figure 2, the input resistor (R
and the input capacitor (C
high pass filter cutoff frequency that is found using Equation
(7).
DD
/2) when charged with a fixed current. The
f
. Thus, pops can be minimized by se-
IR
, C
IL
= 0.33µF) produce a −6dB
RMS
(2.83V
(Continued)
IR
B
, between the
, R
P-P
B
IL
, depends
). Please
= 20kΩ)
(7)
19
As an example when using a speaker with a low frequency
limit of 150Hz, the input coupling capacitor, using Equation
(7), is 0.053µF. The 0.33µF input coupling capacitor shown
in Figure 2 allows the LM4936 to drive a high efficiency, full
range speaker whose response extends below 30Hz.
OPTIMIZING CLICK AND POP REDUCTION
PERFORMANCE
The LM4936 contains circuitry that minimizes turn-on and
shutdown transients or “clicks and pops”. For this discus-
sion, turn-on refers to either applying the power supply volt-
age or when the shutdown mode is deactivated. While the
power supply is ramping to its final value, the LM4936’s
internal amplifiers are configured as unity gain buffers. An
internal current source changes the voltage of the BYPASS
pin in a controlled, linear manner. Ideally, the input and
outputs track the voltage applied to the BYPASS pin. The
gain of the internal amplifiers remains unity until the voltage
on the BYPASS pin reaches 1/2 V
on the BYPASS pin is stable, the device becomes fully
operational. Although the BYPASS pin current cannot be
modified, changing the size of C
time and the magnitude of “clicks and pops”. Increasing the
value of C
ever, this presents a tradeoff: as the size of C
turn-on time increases. There is a linear relationship be-
tween the size of C
typical turn-on times for various values of C
B
reduces the magnitude of turn-on pops. How-
B
and the turn-on time. Below are some
B
DD
alters the device’s turn-on
. As soon as the voltage
B
B
:
increases, the
www.national.com