TDA1400 Tripath Technology, TDA1400 Datasheet - Page 21

• Manufacturer Part Number: TDA1400
• Description: MONO CLASS-T DIGITAL AUDIO AMPLIFIER DRIVER
• Manufacturer: Tripath Technology

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The equation for calculating R
The two resistors, R
used for the direct calculation of the actual VPP and VNN trip voltages without considering the effect of
R
Using the resistor values from above, the actual minimum over voltage turn off points will be:
The other three trip points can be calculated using the same formula but inserting the appropriate
I
the minimum overvoltage turn off and maximum under voltage turn-off for both the VPP and VNN
supplies.
Output Transistor Selection
The key parameters to consider when selecting what n-channel and p-channel MOSFETs to use with the
TDA1400 are drain-source breakdown voltage (BVdss), gate charge (Qg), and on-resistance (R
The BVdss rating of the MOSFET needs to be selected to accommodate the voltage swing between
V
a ‘good’ circuit board layout, a BVdss that is 50% higher than the VPP to VNN voltage swing is a
reasonable starting point. The BVdss rating should be verified by measuring the actual voltages
experienced by the MOSFET in the final circuit.
Ideally a low Qg (total gate charge) and low R
Unfortunately, these are conflicting requirements since R
MOSFET. The design trade-off is one of cost versus performance. A lower R
losses but the associated higher Qg translates into higher switching losses (losses = Qg x 10 x 1.2MHz).
A lower R
lower switching losses but higher I
Gate Resistor Selection
The gate resistors, R
voltage overshoots. They also dissipate a portion of the power resulting from moving the gate charge
each time the MOSFET is switched. If R
Large gate resistors lead to slower MOSFET switching edges which require a larger break-before-make
(BBM) delay.
21
VPPSENSE
SPOS
VPP2
and R
and V
Set
I
VPPSENSE and VNNSENSE, respectively.
R
VPP
VNN
VPP
VNN
VPPSENSE
(or I
DS(ON)
VNN1
VNN2
SNEG
R
VNNSENSE
MIN_OV_TUR
RANGE
VNN2
MIN_OV_TUR
RANGE
=
also means a larger silicon die and higher cost. A higher R
.
as well as any voltage peaks caused by voltage ringing due to switching transients. With
I
or I
VNNSENSE
=
VNN
VPP2
=
=
VNNSENSE
G
3
) current value. As stated earlier, the usable supply range is the difference between
, are used to control MOSFET switching rise/fall times and thereby minimize
VPP
VNN
×
and R
N_OFF
R
N_OFF
VNN1
MIN_OV_TUR
MIN_OV_TUR
can be any of the currents shown in the Electrical Characteristics table for
VNNSENSE
=
VNN2
=
.
R
−
2
(
VPP1
R
compensate for the internal bias points. Thus, R
R
DSON
VNN1
is as follows:
N_OFF
×
N_OFF
G
I
VPPSENSE
losses.
×
is too small, excessive heat can be generated in the driver.
I
VNNSENSE
-
-
DS(ON)
VPP
VNN
(MIN_OV_TU
are desired for the best amplifier performance.
MAX_UV_TUR
MAX_UV_TUR
(MIN_OV_TU
T r i p a t h T e c h n o l o g y , I n c . - P r e l i m i n a r y I n f o r m a t i o n
DS(ON)
RN_OFF)
is inversely proportional to Qg for a typical
N_OFF
RN_OFF)
N_OFF
)
DS(ON)
T D A 1 4 0 0 – R e v . 0 . 6 5 / K L i / 0 2 . 0 6
DS(ON)
means lower cost and
means lower I
VPP1
and R
VNN1
DS(ON)
2
R
can be
DS(ON)
).