MIC2196 Micrel Semiconductor, MIC2196 Datasheet - Page 10

• Manufacturer Part Number: MIC2196
• Description: 400kHz SO-8 Boost Control IC
• Manufacturer: Micrel Semiconductor

MIC2196
A minimum 1 F ceramic capacitor is required to decouple the
V
nected directly between pins 8 (VCC) and 6 (GND). For V
greater than 8V, use a 4.7 F or a 10 F ceramic capacitor to
decouple the VDD pin.
Efficiency Calculation and Considerations
Efficiency is the ratio of output power to input power. The
difference is dissipated as heat in the boost converter. The
significant contributors at light output loads are:
To maximize efficiency at light loads:
The significant contributors to power loss at higher output
loads are (in approximate order of magnitude):
MIC2196
IN
. The capacitor should be placed near the IC and con-
• The VIN pin supply current which includes the
• Core losses in the inductor.
• Use a low gate charge MOSFET or use the
• Use a ferrite material for the inductor core, which
• Resistive on-time losses in the MOSFET
• Switching transition losses in the MOSFET
• Inductor resistive losses
current required to switch the external
MOSFETs.
smallest MOSFET, which is still adequate for the
maximum output current.
has less core loss than an MPP or iron power
core.
IN
10
To minimize power loss under heavy loads:
• Current sense resistor losses
• Output capacitor resistive losses (due to the
• Use logic level, low on resistance MOSFETs.
• Slow transition times and oscillations on the
• For the same size inductor, a lower value will
• Lowering the current sense resistor value will
• Use low ESR output capacitors to minimize the
capacitor’s ESR)
Multiplying the gate charge by the on-resistance
gives a figure of merit, providing a good balance
between switching and resistive power dissipa-
tion.
voltage and current waveforms dissipate more
power during the turn-on and turn-off of the low
side MOSFET. A clean layout will minimize
parasitic inductance and capacitance in the gate
drive and high current paths. This will allow the
fastest transition times and waveforms without
oscillations. Low gate charge MOSFETs will
switch faster than those with higher gate charge
specifications.
have fewer turns and therefore, lower winding
resistance. However, using too small of a value
will increase the inductor current and therefore
require more output capacitors to filter the output
ripple.
decrease the power dissipated in the resistor.
However, it will also increase the overcurrent
limit and may require larger MOSFETs and
inductor components to handle the higher
currents.
power dissipated in the capacitor’s ESR.
August 2004
Micrel