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LM4985 Evaluation Board
User's Guide
Quick Start Guide
2
Connect the I
C signal generation and interface board to a
computer's parallel port.
Install LM4985 control software: "LM4985_Software_ver1-
52."
Amplifier output mode:
For OCL (Output CapacitorLess) mode, place a jumper
across the pins of JP10 and JP11 and across pins 1 and 2 on
JP8.
For C-CUPL (Capacitor Coupled) mode, place a jumper
across pins 2 and 3 on JP8. Leave JP10 and JP11 open.
Apply a 2.3V to 5.0V power supply's positive voltage output
to the "+" pin on jumpers JP1 and JP2. Apply the power
supply's ground return to the "-" on JP1 and JP2.
Connect the supplied 5-wire cable between the I
generation and interface board and the 5-pin connector (JP7
and JP9) on the LM4985 demonstration board.
© 2006 National Semiconductor Corporation
National Semiconductor
Application Note 1452
Kevin Hoskins
May 2006
Apply a stereo audio signal to jumpers JP3 and JP5. Apply
the source's signal and ground to the "+" pin and the "-" pin,
respectively.
Connect a load (≥ 16Ω) to JP4 and another load to JP6.
JP4's "+" pin and JP6's "+" pin carries the output signals from
the two amplifiers found on pins OUT1 and OUT2, respec-
tively.
Apply power. Make measurements. Plug in a pair of head-
phones. Enjoy.
Introduction
To help the user investigate and evaluate the LM4985's
performance and capabilities, a fully populated demonstra-
tion board is available from the Audio Products Group. This
board is shown in Figure 1. Connected to an external power
2
C signal
supply (2.3V to 5V), a signal source and an I
signal source), the LM4985 demonstration board easily dem-
onstrate the amplifier's features.
FIGURE 1. The LM4985 Demonstration Board
AN201849
2
C controller (or
20184902
www.national.com
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Summary of Contents for National Semiconductor LM4985
-
Page 1: Quick Start Guide
For C-CUPL (Capacitor Coupled) mode, place a jumper across pins 2 and 3 on JP8. Leave JP10 and JP11 open. To help the user investigate and evaluate the LM4985’s Apply a 2.3V to 5.0V power supply’s positive voltage output performance and capabilities, a fully populated demonstra- to the “+”... -
Page 2: General Description
General Description Operating Conditions –40˚C ≤ T ≤ 85˚C • Temperature Range The LM4985 is a stereo headphone audio amplifier with an internal digitally controlled volume control. The LM4985 is 2.3V ≤ V ≤ 5.0V • Amplifier Power Supply Voltage optimized to operate over a power supply voltage range of 2.5V to 5.0V. - Page 3 This jumper is used to short the right channel output capacitor C6 when the OCL mode is selected through the I C digital interface. When the LM4985 is used in the C–CUPL mode, leave this jumper open. JP11 This jumper is used to short the left channel output capacitor C5 when the OCL mode is selected through the I C digital interface.
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Page 4: Power Supply Sequencing
Setup will create a folder minimum, and the input MUX set so that IN1 and IN2 corre- named “LM4985” in the “Program” folder on the “C” disk (if spond to OUT1 and OUT2, respectfully (normal stereo). -
Page 5: Pcb Layout Guidelines
(Continued) C interface board to apply a logic low or logic high to the LM4985’s ADR pin according to the radio button that is Use the WAKE UP TIME section to select one of four selected. The LM4985 will respond to either of the ad- different wake-up times available in both OCL and C-CUPL dresses selected in the software’s Address Bit control. - Page 6 Figures 4 through 7 show the different layers used to create The lower middle layer was not routed in this PCB layout. the LM4985 four-layer demonstration board. Figure 4 is the 20184906 Figure 4. Top Silkscreen (Shown 2.6X actual size) 20184903 Figure 5.
- Page 7 Demonstration Board PCB Layout (Continued) 20184904 Figure 6. Upper Middle Layer (Shown 2.6X actual size) 20184905 Figure 7. Bottom Layer (Shown 2.6X actual size) www.national.com...
- Page 8 Typical Demonstration Board Audio Performance (C-CUPL Mode) Typical C-CUPL mode THD+N versus Output Power performance curves at V = 5V, 3.6V, and 2.5V for 16Ω and 32Ω are shown in Figure 8 and Figure 9, respectively. Typical C-CUPL mode THD+N versus Frequency performance curves at V = 5V, 3.6V, and 2.5V for 16Ω...
- Page 9 Typical Demonstration Board Audio Performance (OCL Mode) Typical OCL mode THD+N versus Output Power performance curves at V = 5V, 3.6V, and 2.5V for 16Ω and 32Ω are shown in Figure 12 and Figure 13, respectively. Typical OCL mode THD+N versus Frequency performance curves at V = 5V, 3.6V, and 2.5V for 16Ω...
- Page 10 Register Although barely audible, very low magnitude output tran- Table B1 shows the actions that are implemented by ma- sients may occur when the LM4985’s shutdown mode is nipulating the bits within the two internal I C control deactivated. To ensure that they are silenced, the two slow- registers.
- Page 11 Appendix C Volume Control volume control register in binary fashion increases the vol- ume control setting, reaching full scale at 11111. Table C1 Settings Binary Values shows the value of the gain for each of the 32 binary volume control settings. The minimum volume setting is set to –76dB when 00000 is loaded into the volume control register.
- Page 12 CNT_GND resistance can be very small, but still signifi- Layout, and Mounting cant. It is significant because of the relatively low load im- pedances for which the LM4985 was designed to drive: 16Ω Considerations to 32Ω. The ratio of this voltage divider will determine the...
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Page 13: Revision History
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