Fangtek ft690 User manual

690- 0502273076 www.fangtek.com 1
ft690
2W Mono BTL Audio Power Amplifier
General Description
The ft690 is an audio power amplifier primarily designed
for demanding applications in mobile phones and other
portable communication device applications. It is capable
of delivering 1.25 watts of continuous average power to
an 8ΩBTL load and 2 watts of continuous average
power (DFN only) to a 4ΩBTL load with less than 1%
distortion (THD+N+N) from a 5VDC power supply.
The ft690 was designed specifically to provide high
quality output power with a minimal amount of external
components. The ft690 does not require output coupling
capacitors or bootstrap capacitors, and therefore is ideally
suited for mobile phone and other low voltage
applications where minimal power consumption is a
primary requirement.
The ft690 features a low-power consumption shutdown
mode. To facilitate this, Shutdown may be enabled by
either logic high or low depending on mode selection.
Driving the shutdown mode pin either high or low
enables the shutdown pin to be driven in a likewise
manner to enable shutdown.
The ft690 contains advanced pop & click circuitry which
eliminates noise which would otherwise occur during
turn-on and turn-off transitions.
The ft690 is unity-gain stable and can be configured by
external gain-setting resistors.
Key Specifications
Improved PSRR at 217Hz & 1KHz 66dB
Power Output at 5.0V, 1% THD+N, 4Ω(QFN only)
2W(typ)
Power Output at 5.0V, 1% THD+N, 8Ω1.25W (typ)
Power Output at 3.0V, 1% THD+N, 4Ω600mW (typ)
Power Output at 3.0V, 1% THD+N, 8Ω425mW (typ)
Shutdown Current 0.1μA (typ)
Features
Available in space-saving packages: DFN, MSOP,
WCSP
Ultra low current shutdown mode
Improved pop & click circuitry eliminates noise during
turn-on and turn-off transitions
2.2 - 5.5V operation
No output coupling capacitors, snubber networks or
bootstrap capacitors required
Unity-gain stable
External gain configuration capability
User selectable shutdown High or Low logic Level
Applications
Mobile Phones
PDAs
Portable electronic device
Application Circuit
Figure 1.Typical Audio Amplifier Application Circuit (DFN)
Doc# ft690- 0502273076
December 15, 2006
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Figure 2.Typical Audio Amplifier Application Circuit (MSOP and WCSP)
ORDERING INFORMATION
P/N TEMP RANGE PIN-PACKAGE GAIN(dB)
ft690D -40°C to +85°C 10pin DFN Adj.
ft690M -40°C to +85°C 8pin MSOP Adj.
Ft690W -40°C to +85°C 9pin WCSP Adj.
Ordering Information continued at end of data sheet.
Pin Configurations and Selector Guide appear at end of data sheet.
ABSOLUTE MAXIMUM RATINGS
Unit
Supply voltage, VDD 6.0 V
Storage Temperature −65°C to +150°C
Input Voltage −0.3V to VDD +0.3V
Power Dissipation Internally Limited
ESD Susceptibility 2000V
Junction Temperature 150°C
θJC (MSOP) 56°C/W
θJA (MSOP) 190°C/W
θJC (WCSP) 180°C/W
θJA (DFN) 63°C/W
θJC (DFN) 12°C/W
Lead temperature 1,6 mm (1/16 Inch) from case for 10 seconds 260°C
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RECOMMENDED OPERATING CONDITIONS
MIN YP MAX UNIT
Supplyvoltage,VDD 2.5 5.5 V
High-level input voltage, VIH SHUTDOWN 2 V
Low-level input voltage, VIL SHUTDOWN 0.8 V
Common-mode input voltage, VIC VDD = 2.5 V, 5.5 V, CMRR ≤-60 dB 0.5 VDD-0.8 V
Operating free-air temperature, TA -40 85 °C
Loadimpedance,ZL 6.4 8 Ω
ELECTRICAL CHARACTERISTICS
VDD=5V TA=25°C
Symbol Parameter Conditions Typical Limit Units(Limits)
VIN=0V, IO=0A, No Load 2.5 7 mA (max)
IDD Quiescent Power Supply Current VIN=0V, IO=0A, 8 Ω Load 3 10 mA (max)
ISD Shutdown Current VSD= VSD MODE (WCSP only) 0.1 2.0 μA (max)
VSDIH Shutdown Voltage Input High VSD MODE = VDD 1.5 V
VSDIL Shutdown Voltage Input Low VSD MODE = VDD 1.3 V
VSDIH Shutdown Voltage Input High VSD MODE = GND 1.5 V
VSDIL Shutdown Voltage Input Low VSD MODE = GND 1.3 V
VOS Output Offset Voltage 7 50 mV (max)
9.7 K Ω (max)
ROUT Resistor Output to GND 8.5 7.0 K Ω (min)
Output Power (8 Ω) THD+N=1% (max); f=1kHz 1.25 0.9 W (min)
PO(4Ω) THD+N=1% (max); f=1kHz 2 W
TWU Wake-up time 130 Ms
THD+N Total Harmonic Distortion+Noise PO= 0.5Wrms; f=1kHz 0.2 %
PSRR Power Supply Rejection Ratio Vripple=200mV sine p-p
Input terminated with 10 Ω
66(f=217Hz)
76(f=1kHz) 55 dB (min)
VDD=3V TA=25°C
Symbol Parameter Conditions Typical Limit Units(Limits)
VIN=0V, IO=0A, No Load 1.6 7 mA (max)
IDD Quiescent Power Supply Current VIN=0V, IO=0A, 8 Ω Load 2 9 mA (max)
ISD Shutdown Current VSD= VSD MODE (WCSP only) 0.1 2.0 μA (max)
VSDIH Shutdown Voltage Input High VSD MODE = VDD 1.1 V
VSDIL Shutdown Voltage Input Low VSD MODE = VDD 0.9 V
VSDIH Shutdown Voltage Input High VSD MODE = GND 1.3 V
VSDIL Shutdown Voltage Input Low VSD MODE = GND 1.0 V
VOS Output Offset Voltage 7 50 mV (max)
9.7 K Ω (max)
ROUT Resistor Output to GND 8.5 7.0 K Ω (min)
Output Power (8 Ω) THD+N=1% (max); f=1kHz 425 mW
POOutput Power (4 Ω) THD+N=1% (max); f=1kHz 600 mW
TWU Wake-up time 80 Ms
THD+N Total Harmonic Distortion+Noise PO= 0.25Wrms; f=1kHz 0.1 %
PSRR Power Supply Rejection Ratio Vripple=200mV sine p-p
Input terminated with 10 Ω
66(f=217Hz)
76(f=1kHz) 55 dB (min)
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VDD=2.6V TA=25°C
Symbol Parameter Conditions Typical Limit Units(Limits)
VIN=0V, IO=0A, No Load 1.5 mA (max)
IDD Quiescent Power Supply Current VIN=0V, IO=0A, 8 Ω Load 2 mA (max)
ISD Shutdown Current VSD= VSD MODE (WCSP only) 0.1 μA (max)
VSDIH Shutdown Voltage Input High VSD MODE = VDD 1.0 V
VSDIL Shutdown Voltage Input Low VSD MODE = VDD 0.9 V
VSDIH Shutdown Voltage Input High VSD MODE = GND 1.2 V
VSDIL Shutdown Voltage Input Low VSD MODE = GND 1.0 V
VOS Output Offset Voltage 5 50 mV (max)
9.7 K Ω (max)
ROUT Resistor Output to GND 8.5 7.0 K Ω (min)
Output Power (8 Ω) THD+N=1% (max); f=1kHz 300 mW
POOutput Power (4 Ω) THD+N=1% (max); f=1kHz 400 mW
TWU Wake-up time 70 Ms
THD+N+N Total Harmonic Distortion+Noise PO= 0.15Wrms; f=1kHz 0.1 %
PSRR Power Supply Rejection Ratio Vripple=200mV sine p-p
Input terminated with 10 Ω
66(f=217Hz)
76(f=1kHz) 55 dB (min)
PIN DESCRIPTION
DFN Package MSOP Package
Top View
Order Number ft690D
Top View
Order Number ft690M
WCSP Package
Top View
Order Number ft690W
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Package DFN MSOP WCSP
Shutdown Mode Selectable Low Low
Typical Power Output at 5V,
1% THD+N 2W (RL=4) 1.25W (RL=8Ω) 1.25W (RL=8)
A SD_MODE select pin determines the Shutdown Mode for the DFN package, whether it is an Asserted High or an Asserted Low device,
to activate shutdown.
The SD_MODE select pin is with the MSOP and WCSP packaged devices, shutdown occurs only with an low assertion.
Typical Performance Characteristics
LD and MH Specific Characteristics
THD+N+N vs Frequency
Vdd=5V, RL=8Ω, Po=0.5W
0.01
0.1
1
10
10 100 1000 10000 100000
Frequency (Hz)
THD+N (%)
THD+N+N vs Frequency
Vdd=3V, RL=8Ω, Po=0.25W
0.01
0.1
1
10
10 100 1000 10000 100000
Frequency (Hz)
THD+N (%)
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THD+N+N vs Output Pow er
Vdd=5V, RL=8Ω, f=1KHz
0.01
0.1
1
10
0.01 0.1 1 10
Output Power (W)
THD+N (%)
THD+N+N vs Output Power
Vdd=3V, RL=8Ω, f=1KHz
0.01
0.1
1
10
0.01 0.1 1
Output Power (W)
THD+N (%)
THD+N+N vs Frequency
Vdd=2.6V, RL=8Ω, Po=0.15W
0.01
0.1
1
10
10 100 1000 10000 100000
Freq ue n cy (Hz)
THD+N (%)
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THD+N+N vs Output Pow er
Vdd=2.6V, RL=8Ω, f=1KHz
0.01
0.1
1
10
0.01 0.1 1
Output Power (W)
THD+N (%)
PSRR vs Frequency
Vdd=5V, RL=8Ω, Input=10Ω
-100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
10 100 1000 10000 100000
Frequency (Hz)
PSRR (dB)
PSRR vs Frequency
Vdd=3V, RL=8Ω, Input=10Ω
-100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
10 100 1000 10000 100000
Frequency (Hz)
PSRR (dB)
PSRR vs Frequency
Vdd=2.6V, RL=8Ω, Input=10Ω
-100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
10 100 1000 10000 100000
Frequency (Hz)
PSRR (dB)
Power Dissipation vs Output Power
Vdd=5V, RL=8Ω
0
0.2
0.4
0.6
0.8
1
0 0.5 1 1.5 2
Output Power (W)
Power Dissipation (W)
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Power Dissipation vs Output Power
Vdd=3V, RL=8Ω
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
00.20.40.60.8
Output Power (W)
Power Dissipation (W)
Power Dissipation vs Output Power
Vdd=2.6V, RL=8Ω
0
0.05
0.1
0.15
0.2
0.25
0.3
0 0.1 0.2 0.3 0.4 0.5
Output Power (W)
Power Dissipation (W)
Frequency Response vs Input Capacitor Size
Vdd=5V, RL=8Ω, Cap=0.44uF
-10
-9
-8
-7
-6
-5
-4
-3
-2
-1
0
1
10 100 1000 10000 100000
Frequency (Hz)
Output Level (dB)
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Application Information
BRIDGE CONFIGURATION EXPLANATION
As shown in Figure 1, the ft690 has two internal
operational amplifiers. The first amplifier’s gain is
externally configurable, while the second amplifier is
internally fixed in a unity-gain, inverting configuration.
The closed-loop gain of the first amplifier is set by
selecting the ratio of Rfto Riwhile the second amplifier’s
gain is fixed by the two internal 20kΩresistors. Figure 1
shows that the output of amplifier one serves as the input
to amplifier two which results in both amplifiers
producing signals identical in magnitude, but out of
phase by 180°. Consequently, the differential gain for the
IC is
AVD= 2 *(Rf/Ri)
By driving the load differentially through outputs Vo1
and Vo2, an amplifier configuration commonly referred
to as “bridged mode” is established. Bridged mode
operation is different from the classical single-ended
amplifier configuration where one side of the load is
connected to ground.
A bridge amplifier design has a few distinct advantages
over the single-ended configuration, as it provides
differential drive to the load, thus doubling output swing
for a specified supply voltage. Four times the output
power is possible as compared to a single-ended
amplifier under the same conditions. This increase in
attainable output power assumes that the amplifier is not
current limited or clipped. In order to choose an
amplifier’s closed-loop gain without causing excessive
clipping, please refer to Audio Power Amplifier Design
section.
A bridge configuration, such as the one used in ft690,
also creates a second advantage over single-ended
amplifiers. Since the differential outputs, Vo1 and Vo2,
are biased at half-supply, no net DC voltage exists across
the load. This eliminates the need for an output coupling
capacitor which is required in a single supply,
single-ended amplifier configuration. Without an output
coupling capacitor, the half-supply bias across the load
would result in both increased internal IC power
dissipation and also possible loudspeaker damage.
POWER DISSIPATION
Power dissipation is a major concern when designing a
successful amplifier, whether the amplifier is bridged or
single-ended. A direct consequence of the increased
power delivered to the load by a bridge amplifier is an
increase in internal power dissipation. Since the ft690 has
two operational amplifiers in one package, the maximum
internal power dissipation is 4 times that of a
single-ended amplifier. The maximum power dissipation
for a given application can be derived from the power
dissipation graphs or from Equation 1.
PDMAX = 4*(VDD)2/(2π2RL) (1)
It is critical that the maximum junction temperature
TJMAX of 150°C is not exceeded. TJMAX can be
determined from the power derating curves by using
PDMAX and the PC board foil area. By adding copper foil,
the thermal resistance of the application can be reduced
from the free air value of θJA, resulting in higher PDMAX
values without thermal shutdown protection circuitry
being activated. Additional copper foil can be added to
any of the leads connected to the ft690. It is especially
effective when connected to VDD, GND, and the output
pins. Refer to the application information on the ft690
reference design board for an example of good heat
sinking. If TJMAX still exceeds 150°C, then additional
changes must be made. These changes can include
reduced supply voltage, higher load impedance, or
reduced ambient temperature. Internal power dissipation
is a function of output power.
POWER SUPPLY BYPASSING
As with any amplifier, proper supply bypassing is critical
for low noise performance and high power supply
rejection. The capacitor location on both the bypass and
power supply pins should be as close to the device as
possible. Typical applications employ a 5V regulator
with 10μF tantalum or electrolytic capacitor and a
ceramic bypass capacitor which aid in supply stability.
This does not eliminate the need for bypassing the supply
nodes of the ft690. The selection of a bypass capacitor,
especially CB, is dependent upon PSRR requirements,
click and pop performance, system cost, and size
constraints.
SHUTDOWN FUNCTION
In order to reduce power consumption while not in use,
the ft690 contains shutdown circuitry that is used to turn
off the amplifier’s bias circuitry. In addition, the ft690
contains a Shutdown Mode pin (DFN only), allowing the
designer to designate whether the part will be driven into
shutdown with a high level logic signal or a low level
logic signal. This allows the designer maximum
flexibility in device use, as the Shutdown Mode pin may
simply be tied permanently to either VDD or GND to set
the ft690 as either a "shutdown-high" device or a
"shutdown-low" device, respectively. The device may
then be placed into shutdown mode by toggling the
Shutdown pin to the same state as the Shutdown Mode
pin. For simplicity’s sake, this is called "shutdown same",
as the ft690 enters shutdown mode whenever the two
pins are in the same logic state. The MSOP package
lacks this Shutdown Mode feature, and is permanently
fixed as a ‘Shutdown-low’ device. It is best to switch
between ground and supply for maximum performance.
While the device may be disabled with shutdown
voltages in between ground and supply, the idle current
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may be greater than the typical value of 0.1μA. In either
case, the shutdown pin should be tied to a definite
voltage to avoid unwanted state changes.
In many applications, a microcontroller or
microprocessor output is used to control the shutdown
circuitry, which provides a quick, smooth transition to
shutdown. Another solution is to use a single-throw
switch in conjunction with an external pull-up resistor (or
pull-down, depending on shutdown high or low
application). This scheme guarantees that the shutdown
pin will not float, thus preventing unwanted state
changes.
PROPER SELECTION OF EXTERNAL
COMPONENTS
Proper selection of external components in applications
using integrated power amplifiers is critical to optimize
device and system performance. While the ft690 is
tolerant of external component combinations,
consideration to component values must be used to
maximize overall system quality.
The ft690 is unity-gain stable which gives the designer
maximum system flexibility. The ft690 should be used in
low gain configurations to minimize THD+N+N values,
and maximize the signal to noise ratio. Low gain
configurations require large input signals to obtain a
given output power. Input signals equal to or greater than
1Vrms are available from sources such as audio codecs.
Please refer to the section, Audio Power Amplifier
Design, for a more complete explanation of proper gain
selection.
Besides gain, one of the major considerations is the
closed loop bandwidth of the amplifier. To a large extent,
the bandwidth is dictated by the choice of external
components shown in Figure 1. The input coupling
capacitor, Ci, forms a first order high pass filter which
limits low frequency response. This value should be
chosen based on needed frequency response for a few
distinct reasons.
SELECTION OF INPUT CAPACITOR SIZE
Large input capacitors are both expensive and space
hungry for portable designs. Clearly, a certain sized
capacitor is needed to couple in low frequencies without
severe attenuation. But in many cases the speakers used
in portable systems, whether internal or external, have
little ability to reproduce signals below 100Hz to 150Hz.
Thus, using a large input capacitor may not increase
actual system performance.
In addition to system cost and size, click and pop
performance is effected by the size of the input coupling
capacitor, Ci. A larger input coupling capacitor requires
more charge to reach its quiescent DC voltage (nominally
1/2 VDD). This charge comes from the output via the
feedback and is apt to create pops upon device enable.
Thus, by minimizing the capacitor size based on
necessary low frequency response, turn-on pops can be
minimized.
Besides minimizing the input capacitor size, careful
consideration should be paid to the bypass capacitor
value. Bypass capacitor, CB, is the most critical
component to minimize turn-on pops since it determines
how fast the ft690 turns on. The slower the ft690’s
outputs ramp to their quiescent DC voltage (nominally
1/2 VDD), the smaller the turn-on pop. Choosing CB
equal to 1.0μF along with a small value of Ci(in the
range of 0.1μF to 0.39μF), should produce a virtually
clickless and popless shutdown function. While the
device will function properly, (no oscillations or
motorboating), with CB equal to 0.1μF, the device will be
much more susceptible to turn-on clicks and pops. Thus,
a value of CBequal to 1.0μF is recommended in all but
the most cost sensitive designs.
AUDIO POWER AMPLIFIER DESIGN
A 1W/8ΩAudio Amplifier
Given:
PowerOutput 1Wrms
LoadImpedance 8Ω
InputLevel 1Vrms
InputImpedance 20kΩ
Bandwidth 100Hz–20kHz ± 0.25dB
A designer must first determine the minimum supply rail
to obtain the specified output power. By extrapolating
from the Output Power vs Supply Voltage graphs in the
Typical Performance Characteristics section, the
supply rail can be easily found.
5V is a standard voltage in most applications, it is chosen
for the supply rail. Extra supply voltage creates
headroom that allows the ft690 to reproduce peaks in
excess of 1W without producing audible distortion. At
this time, the designer must make sure that the power
supply choice along with the output impedance does not
violate the conditions explained in the Power
Dissipation section.
Once the power dissipation equations have been
addressed, the required differential gain can be
determined from Equation 2.
(2)
Rf/Ri= AVD/2
From Equation 2, the minimum AVD is 2.83; use AVD = 3.
Since the desired input impedance was 20kΩ, and with a
AVD impedance of 2, a ratio of 1.5:1 of Rfto Riresults in
an allocation of Ri= 20kΩand Rf= 30kΩ. The final
design step is to address the bandwidth requirements
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