FAB2200 Datasheet, PDF (14/33 Pages) Fairchild Semiconductor – Audio Subsystem with Stereo Class-G Headphone Amplifier and 1.2W Mono Class-D Speaker Amplifier

Class-G Headphone Amplifier with
Capacitor Free Outputs
The FAB2200 includes a regulated charge pump that
derives CPV_DD and CPV_SS (the headphone amplifier
power supplies) from VBATT. When the headphone
output amplitude is low, the CPV_DD is 1.3V and CPV_SS is
-1.3V. When needed, CPV_DD and CPV_SS dynamically
increase to 1.8V and -1.8V, respectively, to allow for
higher output amplitudes. The combination of an
efficient regulated charge pump and class-G operation
allows low headphone amplifier power dissipation,
resulting in longer battery run time.
The negative CPV_SS rail allows the headphone amplifier
output to be centered at 0V and eliminates the need for
output DC blocking capacitors.
The FAB2200 headphone outputs can be placed in
High-Impedance Mode by setting the HIZx bits to 1 (see
Table 2). This can be useful if the system’s headphone
jack is shared with other devices. For proper high-
impedance operation, the device must not be in
Shutdown Mode. Voltages on HPL and HPR must not
exceed ±1.8V.
Table 2. Headphone Amplifier Output
Impedance, HIZx=1
Output Impedance (Ω) Frequency (KHz)
11800
40
760
6000
470
13000
Headphone Volume Control Ramp and
Zero-Crossing Detection
The HPRAMP, HPRAMPSPEED, and HPZCD bits
control the headphone amplifiers’ volume controls when
HPxV_OL is changed.
Table 3. Headphone Volume Change Behavior
HPRAMP HPZCD
Behavior When HPxVOL Changes
0
0
Volume changes immediately.
0
1
For each channel, wait until a zero crossing occurs in the input before changing volume. If a
zero crossing does not occur within HPRAMPSPEED, volume is forced to the new setting.
1
0
Volume is ramped to the new setting at a rate of HPRAMPSPEED per step.
Volume is changed by one step when a zero crossing occurs. If a zero crossing does not
1
1
occur within HPRAMPSPEED, a step is forced. Only the first zero crossing within
HPRAMPSPEED triggers a volume change – volume does not change again until the next
HPRAMPSPEED.
Table 4. Headphone Volume Change Timing
HPRAMPSPEED[1:0]
00
01
10
11
Ramp and ZCD Time Between Steps (ms)
0.25
2.00
16.00
128.00
© 2009 Fairchild Semiconductor Corporation
FAB2200 • Rev. 1.0.1
14
www.fairchildsemi.com