YB1680
1.5MHz, 600mA Synchronous Step-Down Converter
turning the main switch off and keeping it
switch and synchronous rectifier. The slope
compensation signal reduces the peak
inductor current as a function of the duty
cycle to prevent sub-harmonic oscillations
at duty cycles greater than 50%.
Conversely the current limit increases as
the duty cycle decreases.
off until the fault is no longer present.
Idle Mode Operation
At very light loads, the YB1680
automatically enters Idle Mode. In the Idle
Mode, the inductor current may reach zero
or reverse on each pulse. The PWM control
loop will automatically skip pulses to
maintain output regulation. The bottom
MOSFET is turned off by the current
reversal comparator, IZERO, and the switch
voltage will ring. This is discontinuous
mode operation, and is normal behavior for
the switching regulator.
Application Information
Setting the Output Voltage
Figure 1 above shows the basic application
circuit with YB1680 adjustable output
version. The external resistor sets the
output voltage according to the following
equation:
Dropout Operation
When the input voltage decreases toward
the value of the output voltage, the YB1680
allows the main switch to remain on for
more than one switching cycle and
increases the duty cycle until it reaches
100%. The output voltage then is the input
voltage minus the voltage drop across the
main switch and the inductor. At low input
supply voltage, the RDS(ON) of the
P-Channel MOSFET increases, and the
efficiency of the converter decreases.
Caution must be exercised to ensure the
heat dissipated not to exceed the maximum
junction temperature of the IC.
R1=300KΩ for all outputs; R2=300KΩ for
V
OUT=1.2V, R2=200KΩ for VOUT=1.5V,
R2=150KΩ for VOUT=1.5V, and R=95.3KΩ
for VOUT=2.5V.
Inductor Selection
For most designs, the YB1680 operates
with inductors of 1μH to 4.7μH. Low
inductance values are physically smaller
but require faster switching, which results in
some efficiency loss. The inductor value
can be derived from the following equation:
Maximum Load Current
Where ΔIL is inductor Ripple Current. Large
value inductors lower ripple current and
small value inductors result in high ripple
currents. Choose inductor ripple current
The YB1680 will operate with input supply
voltage as low as 2.5V, however, the
maximum load current decreases at lower
input due to large IR drop on the main
YB1680 Rev.1.0
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YOBON [ YOBON TECHNOLOGIES,INC. ]
