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A21SP16
3 W filter-free class-D audio power amplifier
Datasheet - production data
 Output power: 1.4 W @ 5 V or 0.45 W @ 3 V
into 8 with 1% THD+N max
Pin connection
 Adjustable gain via external resistors
IN+
GND
OUT-
1/A1
2/A2
3/A3
 Low current consumption 2 mA @ 3 V
VDD
VDD
GND
 Efficiency: 88% typ.
4/B1
5/B2
6/B3
 Signal to noise ratio: 85 dB typ.
IN-
STBY
OUT+
 PSRR: 63 dB typ. @ 217 Hz with 6 dB gain
8/C2
9/C3
7/C1
 PWM base frequency: 250 kHz
IN+: positive differential input
IN-: negative differential input
VDD: analog power supply
GND: power supply ground
STBY: standby pin (active low)
OUT+: positive differential output
OUT-: negative differential output
 Low pop & click noise
 Thermal shutdown protection
 Available in flip-chip 9 x 300 m (Pb-free)
Block diagram
Applications
B1
 Wearable
B2
Vcc
300k
C2 Stdby
C1
A1
Internal
Bias
 Fitness and healthcare
Out+
150k
 Cellular phone
C3
Output
-
InIn+ +
PWM
 PDA
H
Bridge
A3
150k
Description
Out-
Oscillator
The A21SP16 is a differential class-D BTL power
amplifier. It is able to drive up to 2.3 W into a 4 
load and 1.4 W into a 8  load at 5 V. It achieves
outstanding efficiency (88% typ.) compared to
classical Class-AB audio amps.
GND
A2
B3
Features
 Operating from VCC = 2.4 V to 5.5 V
 Standby mode active low
 Output power: 3 W into 4  and 1.75 W into 8 
with 10% THD+N max and 5 V power supply
 Output power: 2.3 W @ 5 V or 0.75 W @ 3 V
into 4 with 1% THD+N max
The gain of the device can be controlled via two
external gain-setting resistors. Pop & click
reduction circuitry provides low on/off switch
noise while allowing the device to start within 5
ms. A standby function (active low) allows the
reduction of current consumption to 10 nA typ.
Table 1. Order codes
Part number
Temperature range
Package
Packing
Marking
A21SP16
-40 °C to +85 °C
Lead-free flip-chip
Tape & reel
62
March 2014
This is information on a product in full production.
DocID026037 Rev 1
1/37
www.st.com
Contents
A21SP16
Contents
1
Absolute maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2
Application component information . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3
Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4
Electrical characteristic curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
5
Application information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
5.1
Differential configuration principle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
5.2
Gain in typical application schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
5.3
Common mode feedback loop limitations . . . . . . . . . . . . . . . . . . . . . . . . 28
For example: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
5.4
Low frequency response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
5.5
Decoupling of the circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
5.6
Wake-up time (tWU) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
5.7
Shutdown time (tSTBY) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
5.8
Consumption in shutdown mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
5.9
Single-ended input configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
5.10
Output filter considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
5.11
Different examples with summed inputs . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Example 1: Dual differential inputs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Example 2: One differential input plus one single-ended input . . . . . . . . . . . . . . . 33
6
Footprint recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
7
Package information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
8
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
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DocID026037 Rev 1
A21SP16
1
Absolute maximum ratings
Absolute maximum ratings
Table 2. Absolute maximum ratings
Symbol
VCC
Vin
Parameter
Value
Unit
6
V
GND to VCC
V
Supply voltage(1), (2)
Input voltage
(3)
Toper
Operating free-air temperature range
-40 to + 85
°C
Tstg
Storage temperature
-65 to +150
°C
150
°C
200
°C/W
Tj
Rthja
Maximum junction temperature
Thermal resistance junction to ambient
Pdiss
Power dissipation
ESD
Human body model
ESD
Machine model
Latch-up
VSTBY
(4)
Internally
2
kV
200
V
200
mA
GND to VCC
V
260
°C
Latch-up immunity
Standby pin voltage maximum voltage
(6)
limited(5)
Lead temperature (soldering, 10 sec)
1. Caution: This device is not protected in the event of abnormal operating conditions, such as for example,
short-circuiting between any one output pin and ground, between any one output pin and VCC, and
between individual output pins.
2. All voltage values are measured with respect to the ground pin.
3. The magnitude of the input signal must never exceed VCC + 0.3V / GND - 0.3V.
4. The device is protected in case of over temperature by a thermal shutdown active @ 150°C.
5. Exceeding the power derating curves during a long period causes abnormal operation.
6. The magnitude of the standby signal must never exceed VCC + 0.3V / GND - 0.3V.
Table 3. Operating conditions
Symbol
Parameter
Value
Unit
2.4 to 5.5
V
0.5 to VCC - 0.8
V
1.4  VSTBY  VCC
GND  VSTBY  0.4
V
Load resistor
4

Thermal resistance junction to ambient (5)
90
°C/W
voltage(1)
VCC
Supply
VIC
Common mode input voltage range(2)
VSTBY
RL
Rthja
Standby voltage input: (3)
Device ON
Device OFF
(4)
1. For VCC from 2.4V to 2.5V, the operating temperature range is reduced to 0°C  Tamb  70°C.
2. For VCC from 2.4V to 2.5V, the common mode input range must be set at VCC/2.
3. Without any signal on VSTBY, the device will be in standby.
4. Minimum current consumption is obtained when VSTBY = GND.
5. With heat sink surface
= 125mm2.
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Application component information
2
A21SP16
Application component information
Table 4. Component information
Component
Functional description
Cs
Bypass supply capacitor. Install as close as possible to the A21SP16 to
minimize high-frequency ripple. A 100nF ceramic capacitor should be
added to enhance the power supply filtering at high frequency.
Rin
Input resistor to program the A21SP16 differential gain (gain = 300 k/Rin
with Rin in k).
Input
capacitor
Due to common mode feedback, these input capacitors are optional.
However, they can be added to form with Rin a 1st order high pass filter with
-3dB cut-off frequency = 1/(2**Rin*Cin).
Figure 1. Typical application schematics
Vcc
B1
Vcc
Vcc
In+
300k
C2 Stdby
GND
GND
Rin
+
C1
Differential
Input
In-
Cs
1u
B2
A1
-
Internal
Bias
GND
Out+
150k
C3
Output
-
InIn+ +
PWM
H
Bridge
SPEAKER
Rin
Input
capacitors
are optional
A3
150k
Out-
Oscillator
TS4962
GND
B3
A2
GND
GND
Vcc
B1
Vcc
Vcc
In+
300k
C2 Stdby
GND
GND
+
Rin
C1
Differential
Input
In-
-
A1
Internal
Bias
4 Ohms LC Output Filter
GND
Out+
150k
C3
15µH
Output
-
InIn+ +
PWM
2µF
H
Bridge
Rin
Input
capacitors
are optional
GND
Cs
1u
B2
GND
A3
150k
Out-
2µF
15µH
Oscillator
GND
TS4962
B3
A2
30µH
GND
1µF
GND
1µF
30µH
8 Ohms LC Output Filter
4/37
DocID026037 Rev 1
Load
A21SP16
3
Electrical characteristics
Electrical characteristics
Table 5. VCC = +5V, GND = 0V, VIC = 2.5V, tamb = 25°C (unless otherwise specified)
Symbol
ICC
Parameter
Conditions
Supply current
(1)
Typ.
Max.
Unit
No input signal, no load
2.3
3.3
mA
No input signal, VSTBY = GND
10
1000
nA
3
25
mV
ISTBY
Standby current
VOO
Output offset voltage
No input signal, RL = 8
Output power
G=6dB
THD = 1% max, F = 1kHz, RL = 4
THD = 10% max, F = 1kHz, RL = 4
THD = 1% max, F = 1kHz, RL = 8
THD = 10% max, F = 1kHz, RL = 8
Pout
Total harmonic
THD + N
distortion + noise
Efficiency Efficiency
Min.
2.3
3
1.4
1.75
W
Pout = 900mWRMS, G = 6dB, 20Hz < F < 20kHz
RL = 8W + 15µH, BW < 30kHz
Pout = 1WRMS, G = 6dB, F = 1kHz,
RL = 8W + 15µH, BW < 30kHz
0.4
Pout = 2WRMS, RL = 4 +  15µH
Pout =1.2WRMS, RL = 8+  15µH
78
88
%
1
%
PSRR
Power supply
rejection ratio with
inputs grounded (2)
F = 217Hz, RL = 8G=6dB
Vripple = 200mVpp
63
dB
CMRR
Common mode
rejection ratio
F = 217Hz, RL = 8G = 6dB,
Vicm = 200mVpp
57
dB
Gain value
Rin in k
Gain
273k 
-----------------R
in
300k 
-----------------R
in
327k 
-----------------R
in
V/V
RSTBY
Internal resistance
from Standby to GND
273
300
327
k
FPWM
Pulse width modulator
base frequency
180
250
320
kHz
SNR
Signal to noise ratio
tWU
Wake-up time
5
10
ms
tSTBY
Standby time
5
10
ms
A-weighting, Pout = 1.2W, RL = 8
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37
Electrical characteristics
A21SP16
Table 5. VCC = +5V, GND = 0V, VIC = 2.5V, tamb = 25°C (unless otherwise specified) (continued)
Symbol
VN
Parameter
Output voltage noise
Conditions
Min.
Typ.
F = 20Hz to 20kHz, G = 6dB
Unweighted RL = 4
A-weighted RL = 4
85
60
Unweighted RL = 8
A-weighted RL = 8
86
62
Unweighted RL = 4 + 15µH
A-weighted RL = 4 + 15µH
83
60
Unweighted RL = 4 + 30µH
A-weighted RL = 4 + 30µH
88
64
Unweighted RL = 8 + 30µH
A-weighted RL = 8 + 30µH
78
57
Unweighted RL = 4 + Filter
A-weighted RL = 4 + Filter
87
65
Unweighted RL = 4 + Filter
A-weighted RL = 4 + Filter
82
59
Max.
Unit
VRMS
1. Standby mode is active when VSTBY is tied to GND.
2. Dynamic measurements - 20*log(rms(Vout)/rms(Vripple)). Vripple is the superimposed sinusoidal signal to VCC @ F = 217Hz.
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DocID026037 Rev 1
A21SP16
Electrical characteristics
Table 6. VCC = +4.2V, GND = 0V, VIC = 2.5V, Tamb = 25°C (unless otherwise specified)(1)
Symbol
ICC
Parameter
Supply current
(2)
Conditions
Typ.
Max.
Unit
No input signal, no load
2.1
3
mA
No input signal, VSTBY = GND
10
1000
nA
3
25
mV
ISTBY
Standby current
VOO
Output offset voltage
No input signal, RL = 8
Output power
G=6dB
THD = 1% max, F = 1kHz, RL = 4
THD = 10% max, F = 1kHz, RL = 4
THD = 1% max, F = 1kHz, RL = 8
THD = 10% max, F = 1kHz, RL = 8
Pout
Total harmonic
THD + N
distortion + noise
Efficiency Efficiency
Min.
1.6
2
0.95
1.2
Pout = 600mWRMS, G = 6dB, 20Hz < F < 20kHz
RL = 8 + 15µH, BW < 30kHz
Pout = 700mWRMS, G = 6dB, F = 1kHz,
RL = 8 + 15µH, BW < 30kHz
W
1
%
0.35
Pout = 1.45WRMS, RL = 4 +  15µH
Pout =0.9WRMS, RL = 8+  15µH
78
88
%
PSRR
Power supply
rejection ratio with
inputs grounded (3)
F = 217Hz, RL = 8G=6dB
Vripple = 200mVpp
63
dB
CMRR
Common mode
rejection ratio
F = 217Hz, RL = 8G = 6dB,
Vicm = 200mVpp
57
dB
Gain value
Rin in k
Gain
273k 
-----------------R in
300k 
-----------------R in
327k 
-----------------R in
V/V
RSTBY
Internal resistance
from Standby to GND
273
300
327
k
FPWM
Pulse width modulator
base frequency
180
250
320
kHz
SNR
Signal to noise ratio
tWU
Wake-uptime
5
10
ms
tSTBY
Standby time
5
10
ms
A-weighting, Pout = 0.9W, RL = 8
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37
Electrical characteristics
A21SP16
Table 6. VCC = +4.2V, GND = 0V, VIC = 2.5V, Tamb = 25°C (unless otherwise specified)(1) (continued)
Symbol
VN
Parameter
Output voltage noise
Conditions
Min.
Typ.
F = 20Hz to 20kHz, G = 6dB
Unweighted RL = 4
A-weighted RL = 4
85
60
Unweighted RL = 8
A-weighted RL = 8
86
62
Unweighted RL = 4 + 15µH
A-weighted RL = 4 + 15µH
83
60
Unweighted RL = 4 + 30µH
A-weighted RL = 4 + 30µH
88
64
Unweighted RL = 8 + 30µH
A-weighted RL = 8 + 30µH
78
57
Unweighted RL = 4 + Filter
A-weighted RL = 4 + Filter
87
65
Unweighted RL = 4 + Filter
A-weighted RL = 4 + Filter
82
59
Max.
Unit
VRMS
1. All electrical values are guaranteed with correlation measurements at 2.5 V and 5 V.
2. Standby mode is active when VSTBY is tied to GND.
3. Dynamic measurements - 20*log(rms(Vout)/rms(Vripple)). Vripple is the superimposed sinusoidal signal to VCC @ F = 217Hz.
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DocID026037 Rev 1
A21SP16
Electrical characteristics
Table 7. VCC = +3.6V, GND = 0V, VIC = 2.5V, Tamb = 25°C (unless otherwise specified)(1)
Symbol
ICC
Parameter
Supply current
(2)
Conditions
Typ.
Max.
Unit
No input signal, no load
2
2.8
mA
No input signal, VSTBY = GND
10
1000
nA
3
25
mV
ISTBY
Standby current
VOO
Output offset voltage
No input signal, RL = 8
Output power
G=6dB
THD = 1% max, F = 1kHz, RL = 4
THD = 10% max, F = 1kHz, RL = 4
THD = 1% max, F = 1kHz, RL = 8
THD = 10% max, F = 1kHz, RL = 8
Pout
Total harmonic
THD + N
distortion + noise
Efficiency Efficiency
Min.
1.15
1.51
0.7
0.9
Pout = 500mWRMS, G = 6dB, 20Hz < F< 20kHz
RL = 8 + 15µH, BW < 30kHz
Pout = 500mWRMS, G = 6dB, F = 1kHz,
RL = 8 + 15µH, BW < 30kHz
W
1
%
0.27
Pout = 1WRMS, RL = 415µH
Pout =0.65WRMS, RL = 815µH
78
88
%
PSRR
Power supply
rejection ratio with
inputs grounded (3)
F = 217Hz, RL = 8G=6dB
Vripple = 200mVpp
62
dB
CMRR
Common mode
rejection ratio
F = 217Hz, RL = 8G = 6dB,
Vicm = 200mVpp
56
dB
Gain value
Rin in k
Gain
273k 
-----------------R in
300k 
-----------------R in
327k 
-----------------R in
V/V
RSTBY
Internal resistance
from Standby to GND
273
300
327
k
FPWM
Pulse width modulator
base frequency
180
250
320
kHz
SNR
Signal to noise ratio
tWU
Wake-uptime
5
10
ms
tSTBY
Standby time
5
10
ms
A-weighting, Pout = 0.6W, RL = 8
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83
dB
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37
Electrical characteristics
A21SP16
Table 7. VCC = +3.6V, GND = 0V, VIC = 2.5V, Tamb = 25°C (unless otherwise specified)(1) (continued)
Symbol
VN
Parameter
Output voltage noise
Conditions
Min.
Typ.
F = 20Hz to 20kHz, G = 6dB
Unweighted RL = 4
A-weighted RL = 4
83
57
Unweighted RL = 8
A-weighted RL = 8
83
61
Unweighted RL = 4 + 15µH
A-weighted RL = 4+ 15µH
81
58
Unweighted RL = 4+ 30µH
A-weighted RL = 4 + 30µH
87
62
Unweighted RL = 8 + 30µH
A-weighted RL = 8+ 30µH
77
56
Unweighted RL = 4 + Filter
A-weighted RL = 4 + Filter
85
63
Unweighted RL = 4 + Filter
A-weighted RL = 4 + Filter
80
57
Max.
Unit
VRMS
1. All electrical values are guaranteed with correlation measurements at 2.5V and 5V.
2. Standby mode is active when VSTBY is tied to GND.
3. Dynamic measurements - 20*log(rms(Vout)/rms(Vripple)). Vripple is the superimposed sinusoidal signal to VCC @ F = 217Hz.
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DocID026037 Rev 1
A21SP16
Electrical characteristics
Table 8. VCC = +3V, GND = 0V, VIC = 2.5V, Tamb = 25°C (unless otherwise specified)(1)
Symbol
ICC
Parameter
Supply current
(2)
Conditions
Typ.
Max.
Unit
No input signal, no load
1.9
2.7
mA
No input signal, VSTBY = GND
10
1000
nA
3
25
mV
ISTBY
Standby current
VOO
Output offset voltage
No input signal, RL = 8
Output power
G=6dB
THD = 1% max, F = 1kHz, RL = 4
THD = 10% max, F = 1kHz, RL = 4
THD = 1% max, F = 1kHz, RL = 8
THD = 10% max, F = 1kHz, RL = 8
Pout
Total harmonic
THD + N
distortion + noise
Efficiency Efficiency
Min.
0.75
1
0.5
0.6
Pout = 350mWRMS, G = 6dB, 20Hz < F < 20kHz
RL = 8 + 15µH, BW < 30kHz
Pout = 350mWRMS, G = 6dB, F = 1kHz,
RL = 8 + 15µH, BW < 30kHz
W
1
%
0.21
Pout = 0.7WRMS, RL = 4 +  15µH
Pout = 0.45WRMS, RL = 8+  15µH
78
88
%
PSRR
Power supply
rejection ratio with
inputs grounded (3)
F = 217Hz, RL = 8G=6dB
Vripple = 200mVpp
60
dB
CMRR
Common mode
rejection ratio
F = 217Hz, RL = 8G = 6dB,
Vicm = 200mVpp
54
dB
Gain value
Rin in k
Gain
273k 
-----------------R in
300k 
-----------------R in
327k 
-----------------R in
V/V
RSTBY
Internal resistance
from Standby to GND
273
300
327
k
FPWM
Pulse width modulator
base frequency
180
250
320
kHz
SNR
Signal to noise ratio
tWU
Wake-up time
5
10
ms
tSTBY
Standby time
5
10
ms
A-weighting, Pout = 0.4W, RL = 8
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dB
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37
Electrical characteristics
A21SP16
Table 8. VCC = +3V, GND = 0V, VIC = 2.5V, Tamb = 25°C (unless otherwise specified)(1) (continued)
Symbol
VN
Parameter
Output voltage noise
Conditions
Min.
Typ.
f = 20Hz to 20kHz, G = 6dB
Unweighted RL = 4
A-weighted RL = 4
83
57
Unweighted RL = 8
A-weighted RL = 8
83
61
Unweighted RL = 4 + 15µH
A-weighted RL = 4 + 15µH
81
58
Unweighted RL = 4 + 30µH
A-weighted RL = 4 + 30µH
87
62
Unweighted RL = 8 + 30µH
A-weighted RL = 8 + 30µH
77
56
Unweighted RL = 4 + Filter
A-weighted RL = 4 + Filter
85
63
Unweighted RL = 4 + Filter
A-weighted RL = 4 + Filter
80
57
Max.
Unit
VRMS
1. All electrical values are guaranteed with correlation measurements at 2.5 V and 5 V.
2. Standby mode is active when VSTBY is tied to GND.
3. Dynamic measurements - 20*log(rms(Vout)/rms(Vripple)). Vripple is the superimposed sinusoidal signal to VCC @ F = 217Hz.
12/37
DocID026037 Rev 1
A21SP16
Electrical characteristics
Table 9. VCC = +2.5V, GND = 0V, VIC = 2.5V, Tamb = 25°C (unless otherwise specified)
Symbol
ICC
Parameter
Supply current
(1)
Conditions
Typ.
Max.
Unit
No input signal, no load
1.7
2.4
mA
No input signal, VSTBY = GND
10
1000
nA
3
25
mV
ISTBY
Standby current
VOO
Output offset voltage
No input signal, RL = 8
Output power
G=6dB
THD = 1% max, F = 1kHz, RL = 4
THD = 10% max, F = 1kHz, RL = 4
THD = 1% max, F = 1kHz, RL = 8
THD = 10% max, F = 1kHz, RL = 8
Pout
Total harmonic
THD + N
distortion + noise
Efficiency Efficiency
Min.
0.52
0.71
0.33
0.42
Pout = 200mWRMS, G = 6dB, 20Hz < F< 20kHz
RL = 8 + 15µH, BW < 30kHz
Pout = 200WRMS, G = 6dB, F = 1kHz,
RL = 8 + 15µH, BW < 30kHz
W
1
%
0.19
Pout = 0.47WRMS, RL = 4 +  15µH
Pout = 0.3WRMS, RL = 8+  15µH
78
88
%
PSRR
Power supply
rejection ratio with
inputs grounded (2)
F = 217Hz, RL = 8G=6dB
Vripple = 200mVpp
60
dB
CMRR
Common mode
rejection ratio
F = 217Hz, RL = 8G = 6dB,
Vicm = 200mVpp
54
dB
Gain value
Rin in k
Gain
273k 
-----------------R in
300k 
-----------------R in
327k 
-----------------R in
V/V
RSTBY
Internal resistance
from Standby to GND
273
300
327
k
FPWM
Pulse width modulator
base frequency
180
250
320
kHz
SNR
Signal to noise ratio
tWU
Wake-up time
5
10
ms
tSTBY
Standby time
5
10
ms
A-weighting, Pout = 1.2W, RL = 8
DocID026037 Rev 1
80
dB
13/37
37
Electrical characteristics
A21SP16
Table 9. VCC = +2.5V, GND = 0V, VIC = 2.5V, Tamb = 25°C (unless otherwise specified) (continued)
Symbol
VN
Parameter
Output voltage noise
Conditions
Min.
Typ.
F = 20Hz to 20kHz, G = 6dB
Unweighted RL = 4
A-weighted RL = 4
85
60
Unweighted RL = 8
A-weighted RL = 8
86
62
Unweighted RL = 4 + 15µH
A-weighted RL = 4 + 15µH
76
56
Unweighted RL = 4 + 30µH
A-weighted RL = 4 + 30µH
82
60
Unweighted RL = 8 + 30µH
A-weighted RL = 8 + 30µH
67
53
Unweighted RL = 4 + Filter
A-weighted RL = 4 + Filter
78
57
Unweighted RL = 4 + Filter
A-weighted RL = 4 + Filter
74
54
Max.
Unit
VRMS
1. Standby mode is active when VSTBY is tied to GND.
2. Dynamic measurements - 20*log(rms(Vout)/rms(Vripple)). Vripple is the superimposed sinusoidal signal to VCC @ F = 217Hz.
14/37
DocID026037 Rev 1
A21SP16
Electrical characteristics
Table 10. VCC = +2.4V, GND = 0V, VIC = 2.5V, Tamb = 25°C (unless otherwise specified)
Symbol
ICC
Parameter
Supply current
(1)
Conditions
Min.
Typ.
Max.
Unit
No input signal, no load
1.7
mA
No input signal, VSTBY = GND
10
nA
3
mV
ISTBY
Standby current
VOO
Output offset voltage
No input signal, RL = 8
Output power
G=6dB
THD = 1% max, F = 1kHz, RL = 4
THD = 10% max, F = 1kHz, RL = 4
THD = 1% max, F = 1kHz, RL = 8
THD = 10% max, F = 1kHz, RL = 8
Total harmonic
distortion + noise
Pout = 200mWRMS, G = 6dB, 20Hz < F< 20kHz
RL = 8 + 15µH, BW < 30kHz
1
Pout = 0.38WRMS, RL = 4 +  15µH
Pout = 0.25WRMS, RL = 8+  15µH
77
86
%
Common mode
rejection ratio
F = 217Hz, RL = 8, G = 6dB,
DVicm = 200mVpp
54
dB
Gain value
Rin in k
Pout
THD + N
Efficiency Efficiency
CMRR
Gain
RSTBY
Internal resistance
from Standby to GND
FPWM
Pulse width modulator
base frequency
SNR
Signal to noise ratio
tWU
tSTBY
VN
0.48
0.65
0.3
0.38
W
%
273k 
-----------------R in
300k 
-----------------R in
327k 
-----------------R
in
V/V
273
300
327
k
250
kHz
80
dB
Wake-up time
5
ms
Standby time
5
ms
Output voltage noise
A Weighting, Pout = 1.2W, RL = 8
F = 20Hz to 20kHz, G = 6dB
Unweighted RL = 4
A-weighted RL = 4
85
60
Unweighted RL = 8
A-weighted RL = 8
86
62
Unweighted RL = 4+ 15µH
A-weighted RL = 4+ 15µH
76
56
Unweighted RL = 4+ 30µH
A-weighted RL = 4+ 30µH
82
60
Unweighted RL = 8+ 30µH
A-weighted RL = 8 + 30µH
67
53
Unweighted RL = 4+ Filter
A-weighted RL = 4+ Filter
78
57
Unweighted RL = 4+ Filter
A-weighted RL = 4+ Filter
74
54
VRMS
1. Standby mode is active when VSTBY is tied to GND.
DocID026037 Rev 1
15/37
37
Electrical characteristic curves
4
A21SP16
Electrical characteristic curves
The graphs included in this section use the following abbreviations:

RL + 15 H or 30 H = pure resistor + very low series resistance inductor

Filter = LC output filter (1 µF + 30 µH for 4  and 0.5 µF + 60 µH for 8 )

All measurements done with Cs1 = 1µF and Cs2 = 100 nF except for PSRR where Cs1
is removed.
Figure 2. Test diagram for measurements
Vcc
1uF
Cs1
100nF
Cs2
+
GND
Cin
GND
Rin
Out+
In+
15uH or 30uH
150k
TS4962
Cin
Rin
4 or 8 Ohms
5th order
or
RL
50kHz low pass
filter
LC Filter
InOut-
150k
GND
Audio Measurement
Bandwidth < 30kHz
Figure 3. Test diagram for PSRR measurements
100nF
Cs2
20Hz to 20kHz
Vcc
GND
4.7uF
GND
Rin
Out+
In+
15uH or 30uH
150k
TS4962
4.7uF
Rin
4 or 8 Ohms
or
5th order
RL
LC Filter
InOut-
150k
GND
GND
5th order
50kHz low pass
Reference
RMS Selective Measurement
Bandwidth=1% of Fmeas
filter
16/37
DocID026037 Rev 1
50kHz low pass
filter
A21SP16
Electrical characteristic curves
Figure 4. Current consumption vs. power
supply voltage
Figure 5. Current consumption vs. standby
voltage
2.5
2.5
Current Consumption (mA)
2.0
1.5
1.0
0.5
0.0
2.0
1.5
1.0
0.5
0.0
0
1
2
3
4
5
Vcc = 5V
No load
Tamb=25°C
0
1
2
2.0
20
1.5
15
1.0
Vcc=5V
Vcc=2.5V
10
Vcc=3.3V
Vcc = 3V
No load
Tamb=25°C
0.5
1.0
1.5
2.0
2.5
G = 6dB
Tamb = 25°C
0
0.0 0.5 1.0 1.5
3.0
Figure 8. Efficiency vs. output power
100
300
40
1.0
Output Power (W)
4.0
4.5
5.0
200
Vcc=5V
RL=4Ω + ≥ 15μH 100
F=1kHz
THD+N≤2%
0
1.5
2.0
200
80
150
Efficiency (%)
60
0.5
3.5
Efficiency
Power Dissipation (mW)
Efficiency (%)
400
20
3.0
100
500
Power
Dissipation
2.5
Figure 9. Efficiency vs. output power
600
Efficiency
2.0
Common Mode Input Voltage (V)
Standby Voltage (V)
0
0.0
5
5
0.5
80
4
Figure 7. Output offset voltage vs. common
mode input voltage
Voo (mV)
Current Consumption (mA)
Figure 6. Current consumption vs. standby
voltage
0.0
0.0
3
Standby Voltage (V)
Power Supply Voltage (V)
60
100
40
Power
Dissipation
20
0
0.0
DocID026037 Rev 1
0.1
0.2
0.3
0.4
Output Power (W)
Vcc=3V
50
RL=4Ω + ≥ 15μH
F=1kHz
THD+N≤2%
0
0.5
0.6
0.7
Power Dissipation (mW)
Current Consumption (mA)
No load
Tamb=25°C
17/37
37
Electrical characteristic curves
A21SP16
Efficiency
100
60
Power
Dissipation
40
50
Vcc=5V
RL=8Ω + ≥ 15μH
F=1kHz
THD+N≤1%
20
0
0.0
0.2
0.4
0.6
Output Power (W)
0.8
Power Dissipation (mW)
80
Efficiency (%)
100
150
50
60
40
Power
Dissipation
20
0
0.0
Figure 12. Output power vs. power supply
voltage
0.1
0.2
0.3
Output Power (W)
3.0
2.0
RL = 4Ω + ≥ 15μH
F = 1kHz
2.5
BW < 30kHz
Tamb = 25°C
2.0
RL = 8Ω + ≥ 15μH
F = 1kHz
BW < 30kHz
1.5 Tamb = 25°C
THD+N=10%
1.5
1.0
THD+N=2%
25
Vcc=3V
RL=8Ω + ≥ 15μH
F=1kHz
THD+N≤1%
0
0.5
0.4
Figure 13. Output power vs. power supply
voltage
Output power (W)
Output power (W)
Efficiency
0
1.0
75
80
Efficiency (%)
100
Figure 11. Efficiency vs. output power
Power Dissipation (mW)
Figure 10. Efficiency vs. output power
THD+N=10%
1.0
0.5
THD+N=1%
0.5
0.0
0.0
2.5
3.0
3.5
4.0
Vcc (V)
4.5
5.0
Figure 14. PSRR vs. frequency
3.0
5.0
-30
-20
-40
Vcc=3V
-50
Vripple = 200mVpp
Inputs = Grounded
G = 6dB, Cin = 4.7μF
RL = 4Ω + 30μH
Tamb = 25°C
-10
PSRR (dB)
-20
-60
-30
-40
Vcc=3V
-50
-60
-70
-70
Vcc=5V
18/37
4.5
0
Vripple = 200mVpp
Inputs = Grounded
G = 6dB, Cin = 4.7μF
RL = 4Ω + 15μH
Tamb = 25°C
-10
-80
3.5
4.0
Vcc (V)
Figure 15. PSRR vs. frequency
0
PSRR (dB)
2.5
20
100
1000
Frequency (Hz)
Vcc=5V
10000 20k
-80
20
DocID026037 Rev 1
100
1000
Frequency (Hz)
10000 20k
A21SP16
Electrical characteristic curves
Figure 16. PSRR vs. frequency
Figure 17. PSRR vs. frequency
0
0
Vripple = 200mVpp
Inputs = Grounded
G = 6dB, Cin = 4.7μF
RL = 4Ω + Filter
Tamb = 25°C
PSRR (dB)
-20
-30
-20
-40
Vcc=3V
-50
Vripple = 200mVpp
Inputs = Grounded
G = 6dB, Cin = 4.7μF
RL = 8Ω + 15μH
Tamb = 25°C
-10
PSRR (dB)
-10
-30
-40
Vcc=3V
-50
-60
-60
-70
-70
Vcc=5V
Vcc=5V
-80
-80
20
100
10000 20k
1000
Frequency (Hz)
20
Figure 18. PSRR vs. frequency
-30
-20
-40
Vcc=3V
-50
Vripple = 200mVpp
Inputs = Grounded
G = 6dB, Cin = 4.7μF
RL = 8Ω + Filter
Tamb = 25°C
-10
PSRR (dB)
-20
-30
-40
Vcc=3V
-50
-60
-60
-70
-70
Vcc=5V
Vcc=5V
-80
20
100
10000 20k
1000
Frequency (Hz)
20
Figure 20. PSRR vs. common mode input
voltage
-10
-20
100
1000
Frequency (Hz)
10000 20k
Figure 21. CMRR vs. frequency
0
0
Vripple = 200mVpp
F = 217Hz, G = 6dB
RL ≥ 4Ω + ≥ 15μH
Tamb = 25°C
RL=4Ω + 15μH
G=6dB
ΔVicm=500mVpp
Cin=4.7μF
Tamb = 25°C
Vcc=2.5V
-20
-30
CMRR (dB)
PSRR(dB)
10000 20k
0
Vripple = 200mVpp
Inputs = Grounded
G = 6dB, Cin = 4.7μF
RL = 8Ω + 30μH
Tamb = 25°C
-10
-80
1000
Frequency (Hz)
Figure 19. PSRR vs. frequency
0
PSRR (dB)
100
Vcc=3.3V
-40
-40
-50
Vcc=5V, 3V
-60
-60
-70
Vcc=5V
-80
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
20
Common Mode Input Voltage (V)
DocID026037 Rev 1
100
1000
Frequency (Hz)
10000 20k
19/37
37
Electrical characteristic curves
A21SP16
Figure 22. CMRR vs. frequency
Figure 23. CMRR vs. frequency
0
0
RL=4Ω + 30μH
G=6dB
ΔVicm=500mVpp
Cin=4.7μF
Tamb = 25°C
-40
-20
CMRR (dB)
CMRR (dB)
-20
RL=4Ω + Filter
G=6dB
ΔVicm=500mVpp
Cin=4.7μF
Tamb = 25°C
-40
Vcc=5V, 3V
Vcc=5V, 3V
-60
-60
20
100
1000
Frequency (Hz)
20
10000 20k
Figure 24. CMRR vs. frequency
100
10000 20k
1000
Frequency (Hz)
Figure 25. CMRR vs. frequency
0
0
RL=8Ω + 15μH
G=6dB
ΔVicm=500mVpp
Cin=4.7μF
Tamb = 25°C
-40
-20
CMRR (dB)
CMRR (dB)
-20
RL=8Ω + 30μH
G=6dB
ΔVicm=500mVpp
Cin=4.7μF
Tamb = 25°C
-40
Vcc=5V, 3V
Vcc=5V, 3V
-60
-60
20
100
1000
Frequency (Hz)
20
10000 20k
Figure 26. CMRR vs. frequency
100
10000 20k
1000
Frequency (Hz)
Figure 27. CMRR vs. common mode input
voltage
-20
0
RL=8Ω + Filter
G=6dB
ΔVicm=500mVpp
Cin=4.7μF
Tamb = 25°C
-40
CMRR(dB)
CMRR (dB)
-20
-30
Vcc=5V, 3V
-40
ΔVicm = 200mVpp
F = 217Hz
G = 6dB
RL ≥ 4Ω + ≥ 15μH
Tamb = 25°C
Vcc=2.5V
-50
Vcc=3.3V
-60
-60
Vcc=5V
20
20/37
100
1000
Frequency (Hz)
10000 20k
-70
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
Common Mode Input Voltage (V)
DocID026037 Rev 1
4.5
5.0
A21SP16
Electrical characteristic curves
Figure 28. THD+N vs. output power
10
10
RL = 4Ω + 30μH
F = 1kHz
G = 6dB
BW < 30kHz
Tamb = 25°C
Vcc=4V
THD + N (%)
RL = 4Ω + 15μH
F = 1kHz
G = 6dB
BW < 30kHz
Tamb = 25°C
THD + N (%)
Figure 29. THD+N vs. output power
Vcc=2.5V
1
Vcc=4V
Vcc=2.5V
1
0.1
0.1
1E-3
0.01
0.1
Output Power (W)
1E-3
1
0.01
0.1
Output Power (W)
1
Figure 31. THD+N vs. output power
10
10
RL = 8Ω + 15μH
F = 1kHz
G = 6dB
BW < 30kHz
Tamb = 25°C
RL = 8Ω + Filter
F = 1kHz
G = 6dB
BW < 30kHz
Tamb = 25°C
Vcc=5V
Vcc=3.3V
THD + N (%)
THD + N (%)
Figure 30. THD+N vs. output power
Vcc=2.5V
1
Vcc=5V
Vcc=3.3V
Vcc=2.5V
1
0.1
0.1
1E-3
0.01
0.1
Output Power (W)
1E-3
1
0.01
0.1
Output Power (W)
1
Figure 33. THD+N vs. output power
10
10
RL = 4Ω + 15μH
F = 1kHz
G = 6dB
BW < 30kHz
Tamb = 25°C
Vcc=2.5V
1
Vcc=4V
Vcc=2.5V
1
0.1
0.1
1E-3
RL = 4Ω + 30μH
F = 1kHz
G = 6dB
BW < 30kHz
Tamb = 25°C
Vcc=4V
THD + N (%)
THD + N (%)
Figure 32. THD+N vs. output power
0.01
0.1
Output Power (W)
1
1E-3
DocID026037 Rev 1
0.01
0.1
Output Power (W)
1
21/37
37
Electrical characteristic curves
A21SP16
Figure 35. THD+N vs. output power
10
10
RL = 8Ω + 15μH
F = 1kHz
G = 6dB
BW < 30kHz
Tamb = 25°C
RL = 8Ω + Filter
F = 1kHz
G = 6dB
BW < 30kHz
Tamb = 25°C
Vcc=5V
Vcc=3.3V
THD + N (%)
THD + N (%)
Figure 34. THD+N vs. output power
Vcc=2.5V
1
1E-3
0.01
0.1
Output Power (W)
1E-3
1
Figure 36. THD+N vs. frequency
1
10
RL=8Ω + 15μH
G=6dB
Bw < 30kHz
Vcc=5V
Tamb = 25°C
Po=0.9W
THD + N (%)
THD + N (%)
0.01
0.1
Output Power (W)
Figure 37. THD+N vs. frequency
10
1
0.1
1000
Frequency (Hz)
RL=8Ω + Filter
G=6dB
Bw < 30kHz
Vcc=5V
Tamb = 25°C
Po=0.9W
1
0.1
Po=0.45W
200
10000
20k
Po=0.45W
200
Figure 38. THD+N vs. frequency
1000
Frequency (Hz)
10000
20k
Figure 39. THD+N vs. frequency
10
10
RL=4Ω + 15μH
G=6dB
Bw < 30kHz
Vcc=3.6V
Tamb = 25°C
1
200
1000
Frequency (Hz)
10000
20k
Po=0.7W
1
Po=0.35W
0.1
Po=0.35W
0.1
RL=4Ω + 30μH
G=6dB
Bw < 30kHz
Vcc=3.6V
Tamb = 25°C
Po=0.7W
THD + N (%)
THD + N (%)
Vcc=2.5V
1
0.1
0.1
22/37
Vcc=5V
Vcc=3.3V
200
DocID026037 Rev 1
1000
Frequency (Hz)
10000
20k
A21SP16
Electrical characteristic curves
Figure 40. THD+N vs. frequency
Figure 41. THD+N vs. frequency
10
10
THD + N (%)
1
RL=4Ω + Filter
G=6dB
Bw < 30kHz
Vcc=2.5V
Tamb = 25°C
Po=0.3W
1
0.1
THD + N (%)
RL=4Ω + 15μH
G=6dB
Bw < 30kHz
Vcc=2.5V
Tamb = 25°C
Po=0.1W
Po=0.3W
0.1
Po=0.1W
200
1000
Frequency (Hz)
10000
20k
0.01
Figure 42. THD+N vs. frequency
100
150
Efficiency
Po=0.9W
1
100
60
Power
Dissipation
40
50
Vcc=5V
RL=8Ω + ≥ 15μH
F=1kHz
THD+N≤1%
20
0.1
Po=0.45W
1000
Frequency (Hz)
200
10000
0
0.0
20k
Figure 44. THD+N vs. frequency
0.2
0.8
1.0
0
10
RL=8Ω + 30μH
G=6dB
Bw < 30kHz
Vcc=3.6V
Tamb = 25°C
Po=0.5W
1
THD + N (%)
RL=8Ω + 15μH
G=6dB
Bw < 30kHz
Vcc=3.6V
Tamb = 25°C
0.1
Po=0.25W
0.01
200
1000
Frequency (Hz)
Po=0.5W
0.1
Po=0.25W
0.01
0.4
0.6
Output Power (W)
Figure 45. THD+N vs. frequency
10
1
20k
80
Efficiency (%)
RL=8Ω + 15μH
G=6dB
Bw < 30kHz
Vcc=5V
Tamb = 25°C
THD + N (%)
10000
Figure 43. THD+N vs. frequency
10
THD + N (%)
1000
Frequency (Hz)
200
Power Dissipation (mW)
0.01
10000
20k
200
DocID026037 Rev 1
1000
Frequency (Hz)
10000
20k
23/37
37
Electrical characteristic curves
A21SP16
Figure 46. THD+N vs. frequency
Figure 47. THD+N vs. frequency
10
10
THD + N (%)
1
RL=8Ω + Filter
G=6dB
Bw < 30kHz
Vcc=2.5V
Tamb = 25°C
Po=0.2W
1
THD + N (%)
RL=8Ω + 15μH
G=6dB
Bw < 30kHz
Vcc=2.5V
Tamb = 25°C
0.1
Po=0.2W
0.1
Po=0.1W
0.01
200
1000
Frequency (Hz)
Po=0.1W
10000
20k
0.01
8
8
6
6
Vcc=5V, 3V
RL=4Ω + 15μH
G=6dB
Vin=500mVpp
Cin=1μF
Tamb = 25°C
2
0
100
1000
Frequency (Hz)
10000 20k
RL=4Ω + 30μH
G=6dB
Vin=500mVpp
Cin=1μF
Tamb = 25°C
2
20
100
8
8
6
6
0
24/37
Vcc=5V, 3V
RL=4Ω + Filter
G=6dB
Vin=500mVpp
Cin=1μF
Tamb = 25°C
2
100
1000
Frequency (Hz)
10000 20k
Vcc=5V, 3V
4
10000 20k
RL=8Ω + 15μH
G=6dB
Vin=500mVpp
Cin=1μF
Tamb = 25°C
2
0
20
1000
Frequency (Hz)
Figure 51. Gain vs. frequency
Differential Gain (dB)
Differential Gain (dB)
Figure 50. Gain vs. frequency
4
20k
Vcc=5V, 3V
4
0
20
10000
Figure 49. Gain vs. frequency
Differential Gain (dB)
Differential Gain (dB)
Figure 48. Gain vs. frequency
4
1000
Frequency (Hz)
200
20
DocID026037 Rev 1
100
1000
Frequency (Hz)
10000 20k
A21SP16
Electrical characteristic curves
Figure 53. Gain vs. frequency
8
8
6
6
Differential Gain (dB)
Differential Gain (dB)
Figure 52. Gain vs. frequency
Vcc=5V, 3V
4
RL=8Ω + 30μH
G=6dB
Vin=500mVpp
Cin=1μF
Tamb = 25°C
2
0
Vcc=5V, 3V
4
0
20
100
1000
Frequency (Hz)
10000 20k
Figure 54. Gain vs. frequency
RL=8Ω + Filter
G=6dB
Vin=500mVpp
Cin=1μF
Tamb = 25°C
2
20
100
1000
Frequency (Hz)
10000 20k
Figure 55. Startup & shutdown time VCC = 5 V,
G = 6 dB, Cin = 1 µF (5 ms/div)
8
Differential Gain (dB)
Vo1
6
Vo2
Vcc=5V, 3V
4
Standby
RL=No Load
G=6dB
Vin=500mVpp
Cin=1μF
Tamb = 25°C
2
0
20
100
Vo1-Vo2
1000
Frequency (Hz)
10000 20k
Figure 56. Startup & shutdown time VCC = 3V,
G = 6 dB, Cin = 1 µF (5 ms/div)
Figure 57. Startup & shutdown time VCC = 5V ,
G = 6 dB, Cin = 100 nF (5 ms/div)
Vo1
Vo1
Vo2
Vo2
Standby
Standby
Vo1-Vo2
Vo1-Vo2
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37
Electrical characteristic curves
A21SP16
Figure 58. Startup & shutdown time VCC = 3 V,
G = 6 dB, Cin = 100 nF (5 ms/div)
Figure 59. Startup & shutdown time
VCC = 5 V, G = 6 dB, No Cin (5 ms/div)
Vo1
Vo1
Vo2
Vo2
Standby
Standby
Vo1-Vo2
Vo1-Vo2
Figure 60. Startup & shutdown time VCC = 3 V,
G = 6 dB, No Cin (5 ms/div)
Vo1
Vo2
Standby
Vo1-Vo2
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A21SP16
Application information
5
Application information
5.1
Differential configuration principle
The A21SP16 is a monolithic fully-differential input/output class D power amplifier. The
A21SP16 also includes a common-mode feedback loop that controls the output bias value
to average it at VCC/2 for any DC common mode input voltage. This allows the device to
always have a maximum output voltage swing, and by consequence, maximizes the output
power. Moreover, as the load is connected differentially compared to a single-ended
topology, the output is four times higher for the same power supply voltage.
The advantages of a full-differential amplifier are:

High PSRR (power supply rejection ratio).

High common mode noise rejection.

Virtually zero pop without additional circuitry, giving a faster start-up time compared to
conventional single-ended input amplifiers.

Easier interfacing with differential output audio DAC.

No input coupling capacitors required due to common mode feedback loop.
The main disadvantage is:

5.2
As the differential function is directly linked to external resistor mismatching, paying
particular attention to this mismatching is mandatory in order to obtain the best
performance from the amplifier.
Gain in typical application schematic
Typical differential applications are shown in Figure 1 on page 4.
In the flat region of the frequency-response curve (no input coupling capacitor effect), the
differential gain is expressed by the relation:
+
AV
diff
-
Out – Out
300
= ------------------------------ = ---------+
R in
In – In
with Rin expressed in k
Due to the tolerance of the internal 150 k feedback resistor, the differential gain will be in
the range (no tolerance on Rin):
327
273
----------  A V  ---------diff
R in
R in
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Application information
5.3
A21SP16
Common mode feedback loop limitations
As explained previously, the common mode feedback loop allows the output DC bias
voltage to be averaged at VCC/2 for any DC common mode bias input voltage.
However, due to Vicm limitation in the input stage (see Table 3: Operating conditions on
page 3), the common mode feedback loop can ensure its role only within a defined range.
This range depends upon the values of VCC and Rin (AVdiff). To have a good estimation of
the Vicm value, we can apply this formula (no tolerance on Rin):
V CC  R in + 2  V IC  150k
V icm = ---------------------------------------------------------------------------2   R in + 150k 
(V)
with
+
-
In + In
V IC = --------------------2
(V)
and the result of the calculation must be in the range:
0.5V  V icm  V CC – 0.8V
Due to the +/-9% tolerance on the 150k resistor, it’s also important to check Vicm in these
conditions:
V CC  R in + 2  V IC  136.5k
V CC  R in + 2  V IC  163.5k
---------------------------------------------------------------------------------  V icm  --------------------------------------------------------------------------------2   R in + 136.5k 
2   R in + 163.5k 
If the result of Vicm calculation is not in the previous range, input coupling capacitors must
be used (with VCC from 2.4 V to 2.5 V, input coupling capacitors are mandatory).
For example:
With VCC = 3 V, Rin = 150 k and VIC = 2.5 V, we typically find Vicm = 2 V and this is lower
than 3V - 0.8 V = 2.2 V. With 136.5 k we find 1.97 V, and with 163.5 k we have 2.02 V.
So, no input coupling capacitors are required.
5.4
Low frequency response
If a low frequency bandwidth limitation is requested, it is possible to use input coupling
capacitors.
In the low frequency region, Cin (input coupling capacitor) starts to have an effect. Cin forms,
with Rin, a first order high-pass filter with a -3dB cut-off frequency:
1
F CL = -----------------------------------2  R in  C in
(Hz)
So, for a desired cut-off frequency we can calculate Cin,
1
C in = -------------------------------------2  R in  F CL
with Rin in  and FCL in Hz.
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(F)
A21SP16
5.5
Application information
Decoupling of the circuit
A power supply capacitor, referred to as CS, is needed to correctly bypass the A21SP16.
The A21SP16 has a typical switching frequency at 250 kHz and output fall and rise time
about 5 ns. Due to these very fast transients, careful decoupling is mandatory.
A 1 µF ceramic capacitor is enough, but it must be located very close to the A21SP16 in
order to avoid any extra parasitic inductance created an overly long track wire. In relation
with dI/dt, this parasitic inductance introduces an overvoltage that decreases the global
efficiency and, if it is too high, may cause a breakdown of the device.
In addition, even if a ceramic capacitor has an adequate high frequency ESR value, its
current capability is also important. A 0603 size is a good compromise, particularly when a
4  load is used.
Another important parameter is the rated voltage of the capacitor. A 1 µF/6.3 V capacitor
used at 5 V, loses about 50% of its value. In fact, with a 5 V power supply voltage, the
decoupling value is about 0.5 µF instead of 1 µF. As CS has particular influence on the
THD+N in the medium-high frequency region, this capacitor variation becomes decisive. In
addition, less decoupling means higher overshoots, which can be problematic if they reach
the power supply AMR value (6 V).
5.6
Wake-up time (tWU)
When the standby is released to set the device ON, there is a wait of about 5 ms. The
A21SP16 has an internal digital delay that mutes the outputs and releases them after this
time in order to avoid any pop noise.
5.7
Shutdown time (tSTBY)
When the standby command is set, the time required to put the two output stages into high
impedance and to put the internal circuitry in shutdown mode, is about 5 ms. This time is
used to decrease the gain and avoid any pop noise during shutdown.
5.8
Consumption in shutdown mode
Between the shutdown pin and GND there is an internal 300 k resistor. This resistor forces
the A21SP16 to be in standby mode when the standby input pin is left floating.
However, this resistor also introduces additional power consumption if the shutdown pin
voltage is not 0 V.
For example, with a 0.4 V standby voltage pin, Table 3: Operating conditions on page 3,
shows that you must add 0.4 V/300 k = 1.3 µA in typical (0.4 V/273 k = 1.46 µA in
maximum) to the shutdown current specified in Table 5 on page 5.
5.9
Single-ended input configuration
It is possible to use the A21SP16 in a single-ended input configuration. However, input
coupling capacitors are needed in this configuration. The schematic in Figure 61 shows a
single-ended input typical application.
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37
Application information
A21SP16
Figure 61. Single-ended input typical application
Vcc
B1
Cs
1u
B2
Vcc
Standby
Cin
GND
Rin
C2 Stdby
300k
Ve
C1
A1
Internal
Bias
GND
Out+
150k
C3
Output
-
InIn+ +
H
Bridge
PWM
SPEAKER
Rin
Cin
A3
150k
Out-
Oscillator
GND
TS4962
GND
A2
B3
GND
All formulas are identical except for the gain (with Rin in k:
AV
sin gle
Ve
300
= ------------------------------- = ---------+
R in
Out – Out
And, due to the internal resistor tolerance we have:
327
273
----------  A V
 ---------sin gle
R in
R in
In the event that multiple single-ended inputs are summed, it is important that the
impedance on both A21SP16 inputs (In- and In+) are equal.
Figure 62. Typical application schematic with multiple single-ended inputs
Vcc
Vek
Standby
B1
C2 Stdby
GND
Ve1
Cin1
Rin1
C1
A1
GND
Ceq
GND
Cs
1u
B2
Vcc
Rink
300k
Cink
Internal
Bias
GND
Out+
150k
C3
Output
-
InIn+ +
PWM
H
Bridge
SPEAKER
Req
A3
150k
Out-
Oscillator
TS4962
GND
A2
B3
GND
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DocID026037 Rev 1
A21SP16
Application information
We have the following equations:
+
300
300
Out – Out = V e1  ------------- +  + V ek  ------------R ink
R in1
(V)
k
C eq =
C
inj
 Cinj
j=1
1
= ---------------------------------------------------2R F
inj
CLj
(F)
1
R eq = ------------------k
1
 --------Rinj
j =1
In general, for mixed situations (single-ended and differential inputs), it is best to use the
same rule, that is, to equalize impedance on both A21SP16 inputs.
5.10
Output filter considerations
The A21SP16 is designed to operate without an output filter. However, due to very sharp
transients on the A21SP16 output, EMI radiated emissions may cause some standard
compliance issues.
These EMI standard compliance issues can appear if the distance between the A21SP16
outputs and loudspeaker terminal is long (typically more than 50 mm, or 100 mm in both
directions, to the speaker terminals). As the PCB layout and internal equipment device are
different for each configuration, it is difficult to provide a one-size-fits-all solution.
However, to decrease the probability of EMI issues, there are several simple rules to follow:

Reduce, as much as possible, the distance between the A21SP16 output pins and the
speaker terminals.

Use ground planes for “shielding” sensitive wires.

Place, as close as possible to the A21SP16 and in series with each output, a ferrite
bead with a rated current at minimum 2 A and impedance greater than 50 at
frequencies above 30 MHz. If, after testing, these ferrite beads are not necessary,
replace them by a short-circuit. Murata BLM18EG221SN1 or BLM18EG121SN1 are
possible examples of devices you can use.

Allow enough footprint to place, if necessary, a capacitor to short perturbations to
ground (see the schematics in Figure 63).
Figure 63. Method for shorting pertubations to ground
Ferrite chip bead
To speaker
From TS4962 output
about 100pF
Gnd
In the case where the distance between the A21SP16 outputs and speaker terminals is
high, it is possible to have low frequency EMI issues due to the fact that the typical operating
frequency is 250 kHz. In this configuration, we recommend using an output filter (as shown
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37
Application information
A21SP16
in Figure 1: Typical application schematics on page 4). It should be placed as close as
possible to the device.
5.11
Different examples with summed inputs
Example 1: Dual differential inputs
Figure 64. Typical application schematic with dual differential inputs
Vcc
Standby
B1
Cs
1u
B2
Vcc
C2 Stdby
300k
R2
E2+
R1
E1+
E1-
C1
A1
Internal
Bias
GND
Out+
150k
C3
Output
-
InIn+ +
PWM
H
Bridge
SPEAKER
R1
A3
150k
E2R2
Out-
Oscillator
GND
A2
B3
TS4962
GND
With (Ri in k):
+
-
+
-
Out – Out
300
A V = ------------------------------ = ---------+
1
R1
E1 – E1
Out – Out
300
- = ---------A V = -----------------------------+
2
R2
E2 – E2
V CC  R 1  R 2 + 300   V IC1  R 2 + V IC2  R 1 
0.5V  ---------------------------------------------------------------------------------------------------------------------------  V CC – 0.8V
300   R 1 + R 2  + 2  R 1  R 2
+
-
+
-
E1 + E1
E2 + E2
V IC = ------------------------ and V IC = -----------------------1
2
2
2
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DocID026037 Rev 1
A21SP16
Application information
Example 2: One differential input plus one single-ended input
Figure 65. Typical application schematic with one differential input plus one singleended input
Vcc
Standby
B1
Cs
1u
B2
Vcc
C2 Stdby
300k
R2
E2+
C1
R1
E1+
E2-
C1
A1
Internal
Bias
C3
Output
-
InIn+ +
PWM
H
Bridge
SPEAKER
R2
A3
150k
GND C1
R1
GND
Out+
150k
Out-
Oscillator
GND
A2
B3
TS4962
GND
With (Ri in k):
+
-
+
-
300
Out – Out
A V = ------------------------------ = ---------+
1
R1
E1
Out – Out
300
A V = ------------------------------ = ---------+
2
R2
E2 – E2
1
C 1 = -----------------------------------2  R 1  F CL
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37
Footprint recommendations
6
A21SP16
Footprint recommendations
Figure 66. Footprint recommendations
500m
75µm min.
100m max.
500m
=250m
=400m typ.
150m min.
=340m min.
500m
500m
Track
Non Solder mask opening
Pad in Cu 18m with Flash NiAu (2-6m, 0.2m max.)
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A21SP16
7
Package information
Package information
In order to meet environmental requirements, ST offers these devices in different grades of
ECOPACK® packages, depending on their level of environmental compliance. ECOPACK®
specifications, grade definitions and product status are available at: www.st.com.
ECOPACK® is an ST trademark.
Figure 67. Pin-out for 9-bump flip-chip (top view)
IN+
GND
OUT-
1/A1
2/A2
3/A3
VDD
VDD
GND
 Bumps are underneath
4/B1
5/B2
6/B3
 Bump diameter = 300m
IN-
STBY
OUT+
8/C2
9/C3
7/C1
Figure 68. Marking for 9-bump flip-chip (top view)
 ST Logo
E
 Symbol for lead-free: E
 Two first XX product code: W2
 third X: Assembly code
XXX
 Three digits date code: Y for year - WW for week
YWW
 The dot is for marking pin A1
Figure 69. Mechanical data for 9-bump flip-chip
1.60 mm
1.60 mm
0.5mm
0.5mm
 0.25mm

Die size: 1.6 mm x 1.6 mm ±30m

Die height (including bumps): 600 m

Bump diameter: 315m 50 m

Bump diameter before reflow: 300 m 10 m

Bump height: 250 m ±40 m

Die height: 350 m ±20 m

Pitch: 500m 50 m

Coplanarity: 50 m max
600µm
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Revision history
8
A21SP16
Revision history
Table 11. Document revision history
36/37
Date
Revision
06-Mar-2014
1
Changes
Initial release.
DocID026037 Rev 1
A21SP16
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