max97200 Maxim Integrated Products, Inc., max97200 Datasheet - Page 9

• Manufacturer Part Number: max97200
• Description: Low-power, Low-offset, Dual Mode, Class H Directdrive Headphone Amplifier
• Manufacturer: Maxim Integrated Products, Inc.

The MAX97200’s Dual Mode, charge pump outputs
either QPVIN/2 in high-efficiency mode or QPVIN in high-
power mode, resulting in a power-supply differential of
1.8V or 3.6V. The charge-pump mode changes based
on the level of the output signal needed. When the
output voltage is small, the voltage rails are reduced to
minimize power consumption. When the output voltage
is large, the voltage rails are increased to accommodate
the larger output need.
High-power mode is similar to Maxim’s traditional
DirectDrive architecture and is best suited for loads
that require high voltage swing. High-efficiency mode
improves power consumption by reducing the power-
supply voltage across the amplifier’s output stage by
half. The reduced power-supply voltage is good for idle
conditions or low-signal level conditions into a head-
phone.
The MAX97200’s internal Class H amplifier uses a class
AB output stage with multiple, discreet power supplies.
This result’s in two power-supply differentials of 1.8V and
3.6V generated from a single 1.8V external supply. The
PVIN/2 power-supply differential is used when the output
voltage requirements are low, and the output is below
V
is used when the output voltage exceeds the high
threshold V
swing. The transition time from high-efficiency mode to
high-power mode occurs when the threshold is crossed.
Figure 2. Inverting and Split Mode Transitions
TH2
as seen in Figure 2. The higher supply differential
Low-Power, Low-Offset, Dual Mode, Class H
TH2
, maximizing output power and voltage
_______________________________________________________________________________________
10ms/div
Dual Mode Charge Pump
Class H Operation
DirectDrive Headphone Amplifier
V
IN_
V
PVDD
PVSS
The switch from high-power mode to high-efficiency
mode occurs 32ms (typ) after the threshold is crossed.
Built-in hysteresis keeps the charge pump from erratic
mode switching when the output voltage is near the high
and low thresholds.
In conventional single-supply audio amplifiers, the out-
put-coupling capacitor contributes significantly to audi-
ble clicks and pops. Upon startup, the amplifier charges
the coupling capacitor to its bias voltage, typically half
the supply. Likewise, on shutdown, the capacitor is dis-
charged. This results in a DC shift across the capacitor,
which appears as an audible transient at the speaker.
Since the MAX97200 does not require output coupling
capacitors, this problem does not arise. Additionally,
the MAX97200 features extensive click-and-pop sup-
pression that eliminates any audible transient sources
internal to the device.
Typically, the output of the device driving the MAX97200
has a DC bias of half the supply voltage. At startup, the
input-coupling capacitor, C
plifier’s DC bias voltage through the MAX97200 input
resistor, R
in an audible click-and-pop. The MAX97200 precharges
the input capacitors when power is applied to ensure
that no audible clicks or pops are heard when SHDN is
pulled high.
The MAX97200 features a 1FA, low-power shutdown
mode that reduces quiescent current consumption and
extends battery life. Shutdown is controlled by the
input. Driving the SHDN input low disables the drive
amplifiers and charge pump and sets the headphone
amplifier output resistance to 100I.
The input capacitor (C
fier input resistance (R
removes the DC bias from the incoming signal. The
AC-coupling capacitor allows the amplifier to bias the sig-
nal to an optimum DC level. Assuming zero source imped-
ance, the -3dB point of the highpass filter is given by:
IN
. This DC shift across the capacitor results
Applications Information
f-
3dB
Click-and-Pop Suppression
IN
IN_
), in conjunction with the ampli-
=
), forms a highpass filter that
2 R C
IN
π
Component Selection
, is charged to the pream-
Input-Coupling Capacitor
IN IN
1
Shutdown
SHDN
9