TLE8386-2EL Datasheet, PDF (23/32 Pages) Infineon Technologies AG – Basic Smart Boost Controller

TLE8386-2EL
Application Information
Current sense resistor R_CS selection:
For control and protection, the TLE8386-2EL measures the power MOSFET current by a current sense resistor
R_CS, which is located between the power MOSFET source and ground. For proper function it is very important:
• To locate the current sense resistor as close as possible to the TLE8386-2EL
• To use short (low resistive and low inductive) traces between the power MOSFET source and ground.
• To use short (low resistive and low inductive) traces between the current sense resistor R_CS highside and
lowside and the pins SWCS and SGND (it is not recommended to use pin GND instead of pin SGND for power
MOSFET current measurement).
• The value of R_CS should be selected to make sure that the maximum peak sense voltage V_SENSEPEAK during
steady state normal operation will be lower than the adjusted current limit threshold (current limit function!). It
is recommended to give a 20% margin.
• The value of R_CS should be selected to make sure that the power MOSFET maximum drain current I_DMAX will
not be exceeded (please refer to power MOSFET data sheet).
The figure below shows the voltage waveform over the current sense resistor R_CS during a switching cycle:
V_{SEN SE}
∆V_SENSE
V_SENSEMAX
V_{S EN SEP EAK}
t
On-Time
Switching Cycle
Figure 10 Sense voltage V_SENSE waveform during a switching cycle
• V_SENSEMAX = maximum average sense voltage at maximum output current I_BO measured during on-time.
• V_SENSEPEAK = maximum peak sense voltage at maximum output current I_BO at end of on-time.
• ∆V_SENSE = ripple voltage across R_CS (switch ripple current) during on-time, represents the peak-to-peak ripple
current in the boost inductor L_BOOST.
The maximum (peak-to-peak) switch current ripple percentage χ (will be needed for further calculations of inductor
values) can be calculated considering the 20% margin by following equation:
χ=
-----------------------------^∆-----V----^S---^E---^N---^S---^E------------------------------
0,80 × V_SWCS – 0,50 × ∆V_SENSE
• V_SWCS = Switch peak over current threshold
• χ is recommended to fall in the range between 0.2 to 0.6 (please refer to calculations in the following chapters)
Data Sheet
21
Rev. 1.0, 2010-10-25