THV6511 Datasheet, PDF (6/9 Pages) THine Electronics, Inc. – THV6511 is a 1 channel boost converter IC

THV6511_Rev.1.00_E
determined by the output capacitor total capacitance,
C_OUT, and the output
VLS_rip  ^{D  IOUT}  I _peak  ESR
F_OSC  C_OUT
I _peak  I _IN  ^{I rip}
2
The first ripple component can be reduced by increasing
C_OUT. Changing C_OUT may require adjustment of
compensation R and C in order to provide adequate
phase margin and loop bandwidth.
The second ripple component can be reduced by
selecting low-ESR ceramic capacitors and using several
smaller capacitors in parallel instead of just one large
capacitor.
[Inductor selection]
To prevent magnetic saturation of the inductor core the
inductor has to be rated for a maximum current larger
than IPK in a given application. Since the chip provides
current limit protection of 1.6A, it is generally
recommended that the inductor be rated at least for 1.6A.
Selection of the inductor requires trade-off between the
physical size (footprint x height) and its electrical
properties (current rating, inductance, resistance). Within
a given footprint and height, an inductor with larger
inductance typically comes with lower current rating and
often larger series resistance. Larger inductance typically
requires more turns on the winding, a smaller core gap or
a core material with a larger relative permeability. An
inductor with a larger physical size has better electrical
properties than a smaller inductor.
It is desirable to reduce the ripple current ΔI_rip in order to
reduce voltage noise on the input and output capacitors.
In practice, the inductor is often much larger than the
capacitors and it is easier and cheaper to increase the size
of the capacitors. The ripple current ΔI_rip is then chosen
the largest possible while at the same time not degrading
the maximum input and output current that the converter
can operate with before reaching the current limit of the
chip or the rated current of the inductor.
I _peak  I _IN  ^{I rip}  I _MAX
2
For example, ΔI_rip could be set to 20% of I_MAX
Protection circuits
Under voltage lock out protection (UVLO)
The UVLO function is carried in order to prevent
malfunction in the state where input voltage is low. A
boost converter is suspended to the power supply voltage
which can carry out operational stability. UVLO is
released by more than 1.9V input voltage. And a boost
converter carries out, after starting soft start operation.
If the feedback voltage pin FB is below 1V, the
THV6511 activates an internal fault timer. If any
condition indicates a continuous fault for the fault timer
duration 54ms, the IC sets the fault latch to shut down its
output except the reference. Once the fault condition is
removed, cycle the input voltage (below the UVLO
falling threshold) to clear the fault latch and reactivate
the device.
Soft start (SS)
The boost converter carries the soft start function in
order to prevent the rush current at a start-up. This
function is to raise output voltage slowly. It is because
overshooting and rush current occur when input voltage
is inputted. This function is available in THV6511only.
This IC uses a soft start circuit to minimize the inrush
current. Connecting a capacitor C_SS between SS pin and
ground determines the soft start time T_SS.
T_SS  ^{1.24V  CSS}
4A
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