TA0103A Tripath Technology Inc., TA0103A Datasheet - Page 13

• Manufacturer Part Number: TA0103A
• Manufacturer: Tripath Technology Inc.

Setting Over-current Threshold
R
Note that R
with R
then to set I
As high-wattage resistors are usually only available in a few low-resistance values (10m:, 25m:
and 50m:), R
values for R
Output Transistor Selection
The key parameters to consider when selecting a MOSFET to use with the TA0103A 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
With a ‘good’ circuit board layout, a BVdss that is 50% higher than the V
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
typical MOSFET. The design trade-off is one of cost versus performance. A lower R
lower I
Qg x 12 x 1.2MHz). A lower R
means lower cost and lower switching losses but higher I
13
SPOS
S
and R
Generating the VN12 voltage per Figure 5 is NOT recommended. Most power supplies only sink
current from the negative terminal and will not be capable of sourcing the current required by
VN12. Furthermore, problems can arise since VN12 will not track movements in V
and V
OCR
2
R
I
where:
R
I
V
when R
SC
SC
DS(ON)
OCR
TOC
S
= 0:, means that R
x R
and R
= 3 x I
S
SC
S
SNEG
= 0.75V typically
determine the value of the over-current threshold, I
.
= Over-current sense threshold voltage (See Electrical Characteristics Table)
will dissipate approximately (I
= 30A, R
S
OCR
losses but the associated higher Qg translates into higher switching losses (losses =
OCR
= (V
as well as any voltage peaks caused by voltage ringing due to switching transients.
OCR
RMS
can be used to adjust for a particular over-current threshold using one of these
= 0:, R
TOC
are in :
= 3 x (P
S
x 9100)/(9100 + R
will be 12.5m: and will only have to dissipate 1.13W on average.
S
= (0.75)/I
OUT
DS(ON)
S
= 25m: and R
/R
L
)
also means a larger silicon die and higher cost. A higher R
V
V
0.5
S
S
SC
(Over-current is typically set for 3 x RMS current)
OCR
RMS
)
)
S
DS(ON)
2
Figure 5
-33V
must dissipate 2.5W on average. If R
x R
5V
S
are desired for the best amplifier performance.
of power. To set an I
2
P GND
R
DS(ON)
DSON
T r i p a t h T e c h n o l o g y , I n c . - T e c h n i c a l I n f o r m a t i o n
VN12
V5
V
V
SPOS
SNEG
A GND
SC
is inversely proportional to Qg for a
losses.
:
DS(ON)
SC
SPOS
TA0103 – Rev 3.3/06.00
of 30A, for example,
).
and V
SNEG
OCR
DS(ON)
SNEG
.
= 9.1K:,
voltage
means
DS(ON)