NR263S Datasheet, PDF (16/29 Pages) Sanken electric – Light Load High Efficiency Synchronous Buck Regulator IC

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7.5 Thermal Shutdown (TSD)
The thermal shutdown circuit detects the IC junction
temperature. When the junction temperature exceeds
the rated value (around 165°C), it shuts-down the output
transistor and turns the output OFF. If the junction
temperature falls below the thermal shutdown rated
value by around 15°C, the operation returns
automatically.
* (Thermal Shutdown Characteristics)
Notes
The circuit protects the IC against temporary heat
generation. It does not guarantee the operation including
reliabilities under the continuous heat generation
conditions, such as short circuit for a long time.
O_出u_力tpu_電t V_圧oltage
Restart
setup
t復em帰pe設rat定ure温度
Shutdown
st_{保eemtu護ppe設rat定ure温度}
Ju_接nct_合ion_温te_度mperature
Fig. 7-8 TSD Operation
7.6 About the "Pulse-Skip-Mode" in the Light-load condition
A NR263S is equipped with the "Pulse-Skip-Mode (naming of our company) " to realize high efficiency in
Light-load. The more load current decrease,it is controlled so that a COMP voltage V_COMP may decrease.
In the condition that the load-current decreases and the V_COMP is under the Vskip (Vskip=Light-load detection
threshold), the operation changes to the Pulse-Skip-Mode when the discontinuous-condition of inductor-current is
longer than the internal timer setup. In the Pulse-Skip-Mode, the peak value of the "Hi-side MOSFET Drain-current
(=IL_P)" is limited to about 600mA. And, the variable-frequency-operation is done that changes the
switching-frequency corresponding to the load. The more switching-frequency decreases, the efficiency in the
light-load condition is possible to improve because the switching-loss decreases in the Hi-side MOSFET and the
Lo-side MOSFET. And, when the load condition changes from light-load to heavy-load,the operation changes from
the Pulse-Skip-Mode to the normal PWM switching mode in a moment.
Notes:
*The V_COMP, the Skip signal, and, the light-load detection threshold Vsk will not be able to confirm directly from the
outside of the package.
*The pulse-skip mode can't be intentional cancellation by the external signal.
Fig. 7-9 Timing chart of the Pulse-Skip-Mode
In addition, pulse-skipping mode frequency as described above will be decreased. There is also a case to be audible
frequency band (20kHz or less). Pulse skip frequency F_skip can be roughly calculated by the following equation.
NR263S series-DSE Rev.1.0
SANKEN ELECTRIC CO.,LTD
16
2016.03.09
http://www.sanken-ele.co.jp/en/
© SANKEN ELECTRIC CO.,LTD. 2016