SA58637 Datasheet, PDF (5/22 Pages) NXP Semiconductors – 2 X 2.2 W BTL audio amplifier

NXP Semiconductors
SA58637
2 × 2.2 W BTL audio amplifier
8. Functional description
The SA58637 is a two-channel BTL audio amplifier capable of delivering 2 × 1.5 W output
power to an 8 Ω load at THD+N = 10 % using a 6 V power supply. It is also capable of
delivering 2 × 2.2 W output power to an 8 Ω load at THD+N = 10 % using a 9 V power
supply. Using the MODE pin, the device can be switched to standby and mute condition.
The device is protected by an internal thermal shutdown protection mechanism. The gain
can be set within a range of 6 dB to 30 dB by external feedback resistors.
8.1 Power amplifier
The power amplifier is a Bridge-Tied Load (BTL) amplifier with a complementary
PNP-NPN output stage. The voltage loss on the positive supply line is the saturation
voltage of a PNP power transistor and on the negative side the saturation voltage of an
NPN power transistor. The total voltage loss is < 1 V.
8.2 Mode select pin (MODE)
The device is in Standby mode (with a very low current consumption) if the voltage at the
MODE pin is greater than V_CC − 0.5 V, or if this pin is floating. At a MODE voltage in the
range between 1.5 V and V_CC − 1.5 V the amplifier is in a mute condition. The mute
condition is useful to suppress plop noise at the output, caused by charging of the input
capacitor. The device is in Active mode if the MODE pin is grounded or less than 0.5 V
(see Figure 6).
8.3 SELECT output configuration
The outputs differentially drives the speakers, so there is no need for coupling capacitors
(see Figure 3). If the voltage at the SELECT pin is in the range between 1.5 V and
V_CC − 1.5 V, or if it is kept floating, then both channels are operational. If the SELECT pin
is set to a logic LOW or grounded, then only the right channel is operational and the left
channel is in Standby mode. If the SELECT pin is set to logic HIGH or connected to V_CC,
then only the left channel is operational and right channel is in Standby mode. Setting the
SELECT pin to logic LOW or a logic HIGH voltage results in a reduction of quiescent
current consumption by a factor of approximately 2. Switching the SELECT pin during
operation is not plop-free, because the input capacitor of the channel which is coming out
of standby needs to be charged first. For plop-free channel selecting the device has first to
be set in mute condition with the MODE pin (between 1.5 V and V_CC − 1.5 V). The
SELECT pin is then set to the new level and after a delay the MODE pin is set to a LOW
level. The delay needed depends on the values of the input capacitors and the feedback
resistors. Time needed is approximately 10 × C1 × (R1 + R2), so approximately
0.6 seconds for the values shown in Figure 3.
Table 4. Control pins MODE and SELECT versus status of output channels
Voltage levels at control pins at V_CC = 5 V; for other voltage levels see Figure 6 and Figure 7.
Control pin
Status of output channel
Typical I_q (mA)
MODE
SELECT
Left channel
Right channel
HIGH^[1]/n.c.^[2]
X^[3]
standby
standby
0
HVCC^[4]
HVCC^[4]/n.c.^[2]
mute
mute
15
LOW^[5]
HVCC^[4]/n.c.^[2]
on
on
15
SA58637_1
Product data sheet
Rev. 01 — 25 February 2008
© NXP B.V. 2008. All rights reserved.
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