Datasheet

TPS28225
TPS28226
www.ti.com SLUS710C –MAY 2006–REVISED APRIL 2010
IMPORTANT NOTE: Any external resistor between PWM input and GND with the value lower than 40kΩ can
interfere with the 3-state thresholds. If the driver is intended to operate in the 3-state mode, any resistor below
40kΩ at the PWM and GND should be avoided. A resistor lower than 3.5kΩ connected between the PWM and
GND completely disables the 3-state function. In such case, the 3-state window shrinks to zero and the lower
3-state threshold becomes the boundary between the UGATE staying low and LGATE being high and vice versa
depending on the PWM input signal applied. It is not necessary to use a resistor <3.5kΩ to avoid the 3-state
condition while using a controller that is 3-state capable. If the rise and fall time of the input PWM signal is
shorter than 250ns, then the driver never enter into the 3-state mode.
In the case where the low-side MOSFET of a buck converter stays on during shutdown, the 3-state feature can
be fused to avoid negative resonent voltage across the output capacitor. This feature also can be used during
start up with a pre-biased output in the case where pulling the output low during the startup is not allowed due to
system requirements. If the system controller does not have the 3-state feature and never goes into the
high-impedance state, then setting the EN/PG signal low will keep both gate drive outputs low and turn both low-
and high-side MOSFETs OFF during the shut down and start up with the pre-biased output.
The self-adjustable input circuit accepts wide range of input pulse amplitudes (2V up to 13.2V) allowing use of a
variety of controllers with different outputs including logic level. The wide PWM input voltage allows some
flexibility if the driver is used in secondary side synchronous rectifier circuit. The operation of the TPS28225/6
with a 12-V input PWM pulse amplitude, and with V
DD
= 7.2V and V
DD
= 5V respectively is shown in Figure 22
and Figure 23.
Figure 22. 12-V PWM Pulse at V
DD
= 7.2 V Figure 23. 12-V PWM Pulse at V
DD
= 5 V
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