
Preliminary Data Sheet
TDA21201
Page 7
Apr-29, 2002
being fully On at a VCC level slightly greater than the threshold.
Bootstrapping
Turning on and off the High side MOSFET is done internally by the Driver. The
TDA21201 does not require any external bootstrap components such as a
capacitor or diode. Just apply GND, Vcc = 12 V, and the PWM signal of the
Controller to it and the Integrated Switch will operate.
Input filter / Output filter / Converter Stability
The Integrated Switch TDA21201 is a new solution to implement the power
semiconductor components in a DC/DC converter. It offers many advantages
to the user. However, the basic behavior with respect to the voltages, the
currents and the timing remains unchanged. Therefore, any of the rules and
procedures applied to design DC/DC converters using discrete MOSFETs and
Drivers apply in the same way to converters using the Integrated Switch –
except the worries regarding dead time control, lowest impedance in the AC
loop, elevated driver temperatures etc.
Current sense
Any of the commonly used current sense techniques are supported by the
Integrated Switch. For Low side sensing measure the voltage drop across the
GND pins and the OUT pin (or the tab when using the SMD version) during
the Low side switch’s On-time (Vin = Low). The High side MOSFET is sensed
across the Vcc and the OUT pin (or the tab when using the SMD version) of
the Integrated Switch during its On-time (Vin = High). Inductor sensing is
implemented outside of the integrated switch the usual way.
Resistor sensing using a separate resistor in the Input capacitor
à
High side
MOSFET (Vcc pin) path is possible but not recommended. This current sense
approach introduces ample stray inductance in the AC current loop (+terminal
of the input capacitor
à
High side MOSFET
à
Low side MOSFET
à
GND
à
-terminal of the input capacitor). This results in a very noisy Vcc line especially
during the switching period and a non-optimized switching behavior of the
Integrated Switch. This in turn, increases the switching losses and the device
temperature and lowers the efficiency.
Output current scalability
The converter output current can be chosen in a wide range by selecting the
appropriate number of phases. At a given number of phases the current per
phase (= current per TDA21201) and in turn the overall converter output
current is set by application requirements, e.g. the switching frequency, and by
environmental conditions, e.g. ambient temperature and the thermal
resistance of the TDA21201 to ambient. As a reference, one TDA21201
generates roughly 3.2 W @ 15 A RMS and 250 kHz (V
CC
= 12 V, V
O
= 1.6 V).
This amount of loss can be dissipated by the SMD version of the Integrated
Switch on a regular motherboard using proper thermal design techniques.
Greater phase currents result in higher losses; and higher switching