TPS92561 Datasheet, PDF (12/31 Pages) Texas Instruments – Phase Dimmable, Single Stage Boost Controller for LED Lighting

TPS92561
SLVSCD1C – DECEMBER 2013 – REVISED NOVEMBER 2015
8 Application and Implementation
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NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
8.1 Application Information
8.1.1 Setting the Output Current
Using the desired ADJ reference voltage, the input current can be calculated using Equation 3.
I_in
V_ADJ
R _SENSE
where
• V_ADJ can be DC, rectified AC derived, or other source.
(3)
If V_ADJ is derived from a voltage divider from the input rectified AC, we can solve for the R9 resistor divider value
based on, for example, a V_ADJ voltage of 150 mV, an R17 value of 374 Ω, and the average value of the sine
wave:
R9 ^{VINRMS u 0.9 u R17} R17
V_ADJ
(4)
TPS92561
GATE
SRC
VP
OVP
Rectified
AC
R9
VCC ADJ
R17
SEN GND
Figure 11. TPS92561 ADJ Connection
To find the R_SENSE value, where ƞ is the converter efficiency, assume 0.9.
R_SENSE
V_{IN RMS} u V_ADJ u K
V_LED u I_LED
(5)
8.1.2 Selecting an Inductance
The TPS92561 device is hysteretic. Therefore, switching transitions are based on the sensed current in the
inductor. There is no direct control of the switching frequency other then the relationship of the comparator
hysteresis to the inductor ripple. A typical switching frequency of an off-line converter using a rectified AC
injected reference could vary up to 50 kHz over a line cycle. This creates a spread-spectrum effect and helps
reduced conducted EMI.
A typical line injected (using a divided down rectified AC as the reference) hysteretic boost converter reaches the
peak switching frequency when V_LED = 2 × V_{RECTIFIED AC}, or when the duty cycle D = 0.5. We call this operating
point V_IN-FSW-PK. Use this voltage as the typical operating point for the design equations. Solve for the V_IN-FSW-PK
term based on Equation 6.
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