BD81A04AMUV-M Datasheet, PDF (10/37 Pages) Rohm – 4ch White LED Driver with Buck-Boost and Built-in FET (32 LED Maximum)

BD81A04AMUV-M BD81A04AEFV-M
(3) Buck-Boost DC/DC Converter Oscillation Frequency (fosc)
10000
RRT vs Fosc
Datasheet
1000
100
1
10
100
RRT[kΩ]
Figure 16. fosc vs R_RT
The regulator’s internal triangular wave oscillation frequency can be set via a resistor connected to the RT pin (pin 4). This
resistor determines the charge/discharge current to the internal capacitor, thereby changing the oscillating frequency.
Please set the resistance of R_RT using the data mentioned above and the logical equation mentioned below as reference.
( ) fosc[kHz] = 81× 10⁵ R_RT [kΩ] × α
Where:
81Ê·10⁵ is the constant value in IC (+-5%)
α is the adjustment factor
(R_T :α = 41kΩ: 1.01, 27kΩ: 1.00 , 18kΩ: 0.99, 10 kΩ: 0.98, 4.7kΩ: 0.97, 3.9kΩ: 0.96 )
A resistor in the range of 3 kΩ to 41 kΩ is recommended. Settings that deviate from the frequency range shown above may
cause switching to stop, and proper operation cannot be guaranteed.
(4) External Synchronization Oscillation Frequency (f_SYNC)
The clock signal input to SYNC terminal can be performed from the outside therefore the internal oscillation frequency can
be synchronized externally.
Do not switch from external to internal oscillation of the DC/DC converter if an external synchronization signal is present on
the SYNC pin and the clock input to SYNC terminal is valid only in rising edge.
As for the external input frequency, the input of the internal oscillation frequency ± 20% decided in RT terminal resistance
is recommended.
(5) Soft Start Function (SS)
The soft-start (SS) limits the current and slows the rise-time of the output voltage during the start-up, and hence leads to
prevention of the overshoot of the output voltage and the inrush current. If you don’t use soft-start function, please set SS
terminal open. For the computation of SS time, please refer to the formula on page 19.
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