A7116
AiT Semiconductor Inc.
www.ait-ic.com
DC-DC CONVERTER/ BUCK (STEP-DOWN)
1.5MHz, 700mA SYNCHRONOUS WITH LOW QUIESCENT CURRENT
Setting the Output Voltage
Figure 1 above shows the basic application circuit with A7116 adjustable output version. The external
resistor sets the output voltage according to the following equation:
R2
R1
VOUT = 0.6V × 1+
R1= 200kΩ for all outputs; R2= 200kΩ for VOUT=1.2V, R2=300kΩ for VOUT =1.5V, R2=400kΩ for VOUT =1.8V,
and R2=900kΩ for VOUT =3.3V.
Inductor Selection
For most designs, the A7116 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:
VOUT
×
(
VIN −VOUT
)
L =
VIN × ∆IL × fOSC
Where ∆IL is inductor Ripple Current. Large value inductors lower ripple current and small value inductors
result in high ripple currents. Choose inductor ripple current approximately 35% of the maximum load current
700mA, or ∆IL =245mA.
For output voltages above 2.0V, when light-load efficiency is important, the minimum recommended inductor
is 2.2µH. For optimum voltage-positioning load transients, choose an inductor with DC series resistance in the
50mΩ to 150mΩ range. For higher efficiency at heavy loads (above 200mA), or minimal load regulation (but
some transient overshoot), the resistance should be kept below 100mΩ. The DC current rating of the
inductor should be at least equal to the maximum load current plus half the ripple current to prevent core
saturation (600mA+105mA). Table 1 lists some typical surface mount inductors that meet target applications
for the A7116.
REV1.2
- JAN 2009 RELEASED, MAY 2016 UPDATED -
- 11 -
AITSEMI [ AiT Semiconductor ]
