BL8076
UVLO and Thermal Shutdown
If VIN drops below 2V, the UVLO circuit inhibits switching. Once VIN rises above 2.1V, the UVLO clears, and the soft-start
sequence activates. Thermal-overload protection limits total power dissipation in the device. When the junction
temperature exceeds TJ= +160°C, a thermal sensor forces the device into shutdown, allowing the die to cool. The
thermal sensor turns the device on again after the junction temperature cools by 15°C, resulting in a pulsed output
during continuous overload conditions. Following a thermal-shutdown condition, the soft-start sequence begins.
DESIGN PROCEDURE
Inductor Selection
The peak-to-peak ripple is limited to 30% of the
maximum output current. This places the peak current
far enough from the minimum overcurrent trip level to
ensure reliable operation while providing enough current
ripples for the current mode converter to operate stably.
In this case, for 2A maximum output current, the
maximum inductor ripple current is 667 mA. The
inductor size is estimated as following equation:
L
IDEAL
=(V
IN(MAX)
-V
OUT
)/I
RIPPLE
*D
MIN
*(1/F
OSC
)
Therefore,
for V
OUT
=1.8V,
The inductor values is calculated to be L = 0.60μH.
Choose 1μH
And for V
OUT
=1.2V,
The inductor values is calculated to be L = 0.469μH.
Choose 0.47μH
The resulting ripple is
I
RIPPLE
=(V
IN(MAX)
-V
OUT
)/L
ACTUAL
*D
MIN
*(1/F
OSC
)
When,
V
OUT
=1.8V, I
RIPPLE
= 403mA
V
OUT
=1.2V, I
RIPPLE
= 665mA
Output Capacitor Selection
For most
applications a nominal 10μF or 22μF
capacitor is suitable. The BL8076 internal
compensation is designed for a fixed corner
frequency that is equal to
FC=
= 50Khz
For example, for V
OUT
=1.8V, L=1μH, C
OUT
=10μF, for V
OUT
=1.2V, L=0.47μH, C
OUT
=22μF
Setting Output Voltage
Output voltages are set by external resistors. The FB_
threshold is 0.6V.
R
TOP
= R
BOTTOM
x [(V
OUT
/ 0.6) - 1]
Guidelines for Input Capacitor and Output Capacitor
The input capacitor in a DC-to-DC converter reduces
current peaks drawn from the battery or other input
power source and reduces switching noise in the
controller. The impedance of the input capacitor at
the switching frequency should be less than that of
the input source so high-frequency switching currents
do not pass through the input source. The output
capacitor keeps output ripple small and ensures
control-loop stability. The output capacitor must also
have low impedance at the switching frequency.
Ceramic, polymer, and tantalum capacitors are
suitable, with ceramic exhibiting the lowest ESR and
high-frequency impedance. Output ripple with a
ceramic output capacitor is approximately as follows:
V
RIPPLE
= IL
(PEAK)
[1 / (2π x f
OSC
x C
OUT
)]
If the capacitor has significant ESR, the output ripple
component due to capacitor ESR is as follows:
V
RIPPLE(ESR)
= IL
(PEAK)
x ESR
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