TA0103A View Datasheet(PDF) - Unspecified
Part Name
Description
View to exact match
TA0103A Datasheet PDF : 18 Pages
| |||
Tripath Technology, Inc. - Technical Information
The following table lists BVdss, Qg and RDS(ON) for MOSFETs that Tripath has used with the
TA0103A:
Mfg. Part Number
ST STW34NB20
ST STW38NB20
ST STP19NB20
IR IRF640
BVdss
200
200
200
200
Qg (Max)
(nanoCoulombs)
80
95
40
70
RDS(ON) (Max)
(Ohms)
0.075
0.065
0.18
0.18
Gate Resistor Selection
The gate resistors, RG, are used to control MOSFET switching rise/fall times and thereby minimize
voltage overshoots. They also dissipate a portion of the power resulting from moving the gate
charge each time the MOSFET is switched. If RG is too small, excessive heat can be generated in
the driver. Large gate resistors lead to slower MOSFET switching, which requires a larger break-
before-make (BBM) delay. Tripath recommends using an RG of 10Ω when the Qg of the MOSFET is
less than 70nC and 5.6Ω when the Qg is greater than 70nC.
Break-Before-Make (BBM) Timing Control
The half-bridge power MOSFETs require a deadtime between when one transistor is turned off and
the other is turned on (break-before-make) in order to minimize shoot through currents. BBM0 and
BBM1 are logic inputs (connected to logic high or pulled down to logic low) that control the break-
before-make timing of the output transistors according to the following table. Note that if either
BBM0 or BBM1 are left floating, they are pulled to a logic low level internal to the TA0103A.
BBM1
0
0
1
1
BBM0
0
1
0
1
Delay
145nS
105nS
65nS
25nS
The tradeoff involved in making this setting is that as the delay is reduced, distortion levels improve
but shoot-through and power dissipation increase. Since the actual amount of BBM required is
dependent upon other component values and circuit board layout, the value selected should be
verified in the actual application circuit/board. It should also be verified under maximum temperature
and power conditions since shoot-through in the output MOSFETs can increase under these
conditions, possibly requiring a higher BBM setting than at room temperature.
Clamping Diodes
The purpose of the diode, D, across each of the output MOSFETs is to clamp the voltages the
MOSFET experiences to levels within its rating to prevent damage. Tripath recommends that fast-
recovery or schottky diodes be used for this purpose (depending on the supply voltage used). The
breakdown voltage rating of this diode should be similar to that of the MOSFET. Also, the forward
voltage drop of this diode should be less than that of the internal body diode of the MOSFET.
MOSFET Bypass Capacitor
Bypass capacitors, CBY, are necessary for each output MOSFET at the nodes shown in the
Test/Application Circuit to damp voltage ringing at these nodes due to the high currents flowing
through the parasitic (circuit board trace) inductance. CBY should be 0.1uF and have the appropriate
voltage rating. They should be physically located as close to the MOSFET leads as possible.
14
TA0103 – Rev 3.3/06.00
|
|
Share Link: 