Datasheet

Datasheet

5/36

BD81A24MUV-M/EFV-M

TSZ02201-0T3T0C600070-1-2

© 2016 ROHM Co., Ltd. All rights reserved.

2016.10.19 Rev.003

www.rohm.com

TSZ22111・15・001

(3) Buck-Boost DC/DC Converter Oscillation Frequency (FOSC)

Figure 8. RRT vs FOSC

DCDC oscillation frequency can be set via a resistor connected to the RT pin. This resistor determines the charge/discharge

current to the internal capacitor, thereby changing the oscillation frequency. Please set the resistance of RRTusing the above

data and below equation.

[

] =(81 × 10

[ Ω]

⁄

)×

Where:

α is the adjustment factor

(RRT: 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 3.6 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 (FSYNC)

If the clock signal input to SYNC terminal, the internal oscillation frequency can be synchronized externally.

Do not switch from external to internal oscillation if the DC/DC converter is active.

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) function can limits the start up current and output rise-time slowly if the capacitor connected to SS

terminal. It is available for prevention of output voltage overshoot and inrush current. If you don’t use soft-start function,

please set SS terminal open. For the calculation of SS time, please refer to the formula on page 24.

(6) Max Duty

If this IC operates by DCDC switching Max Duty, it would not output expect voltage and LED current decrease or LED

current OFF by SCP. Please set load condition and external parts for DCDC switching Duty does not reach Max Duty.

200

2000

1

10

100

RRT [kohm]

RRT vs FOSC