MAX9709 Maxim Integrated Products, MAX9709 Datasheet - Page 13

• Manufacturer Part Number: MAX9709
• Description: 25W/50W Filterless Spread-Spectrum Stereo/Mono Class D Amplifier
• Manufacturer: Maxim Integrated Products

TEMP returns high once the junction temperature cools
below the set threshold minus the thermal hysteresis. If
TEMP is connected to either MUTE or SS, the audio
output resumes. The temperature threshold is set by
the TH0, TH1, and TH2 inputs as shown in Table 1. An
RC filter may be used to eliminate any transient at the
TEMP output as shown in Figure 3.
If TH2 = TH1 = TH0 = HIGH, it is likely that the MAX9709
enters thermal shutdown without tripping the thermal
flag.
The MAX9709 features four pin-selectable gain settings;
see Table 2.
Figure 3. An RC Filter Eliminates Transient During Switching
Table 1. MAX9709 Junction Temperature
Threshold Setting
Table 2. MAX9709 Gain Setting
TEMPERATURE
JUNCTION
High
High
(°C)
Low
Low
100
110
120
129
139
158
G1
80
90
TEMP
V
______________________________________________________________________________________
DIGITAL
10kΩ
25W/50W, Filterless, Spread-Spectrum,
High
High
High
High
TH2
Low
Low
Low
Low
10kΩ
High
High
Low
Low
G2
High
High
High
High
TH1
Low
Low
Low
Low
Gain Selection
0.1µF
Stereo/Mono, Class D Amplifier
GAIN (dB)
29.5
22
25
36
TO DIGITAL
INPUT
High
High
High
High
TH0
Low
Low
Low
Low
The MAX9709 features three switching frequencies in
the FFM mode (Table 3). In this mode, the frequency
spectrum of the Class D output consists of the funda-
mental switching frequency and its associated harmon-
ics (see the Wideband Output Spectrum graph in the
Typical Operating Characteristics). Select one of the
three fixed switching frequencies such that the harmon-
ics do not fall in a sensitive band. The switching fre-
quency can be changed any time without affecting
audio reproduction.
The MAX9709 features a unique, patented spread-
spectrum (SSM) mode that flattens the wideband spec-
tral components, improving EMI emissions that may be
radiated by the speaker and cables. This mode is
enabled by setting FS1 = FS2 = high. In SSM mode, the
switching frequency varies randomly by ±4% around
the center frequency (200kHz). The modulation scheme
remains the same, but the period of the triangle wave-
form changes from cycle to cycle. Instead of a large
amount of spectral energy present at multiples of the
switching frequency, the energy is now spread over a
bandwidth that increases with frequency. Above a few
megahertz, the wideband spectrum looks like white
noise for EMI purposes. SSM mode reduces EMI com-
pared to fixed-frequency mode. This can also help to
randomize visual artifacts caused by radiated or supply
borne interference in displays.
The MAX9709 SYNCIN input allows the Class D amplifi-
er to switch at a frequency defined by an external clock
frequency. Synchronizing the amplifier with an external
clock source may confine the switching frequency to a
less sensitive band. The external clock frequency range
is from 600kHz to 1.2MHz and can have any duty cycle,
but the minimum pulse must be greater than 100ns.
SYNCOUT is an open-drain clock output for synchro-
nizing external circuitry. Its frequency is four times the
amplifier’s switching frequency and it is active in either
internal or external oscillator mode.
Table 3. Switching Frequencies
FS1
0
0
1
1
FS2
0
1
0
1
Spread-Spectrum Modulation (SSM) Mode
Fixed-Frequency Modulation (FFM) Mode
FREQUENCY (kHz)
SYNCOUT
200 ±4
200
250
160
Synchronous Switching Mode
Operating Modes
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Spread-spectrum
Fixed-frequency
Fixed-frequency
Fixed-frequency
MODULATION
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