BD9763FVM Datasheet, PDF (6/12 Pages) Rohm – Single-output Step-up,High-efficiency Switching Regulator (Controller Type)

BD9763FVM
(5) Setting the oscillator frequency
Refer to Fig.5 and determine Timing resistor (RRT) when setting the oscillating frequency.
Oscillating　frequency　vs.　Timing　resistance
10000
Technical Note
1000
100
1
10
100
Timing　resistance　(RT) 　[kΩ]
1000
Fig.8 Oscillating frequency – Timing resistance (RRT)
(6) Setting the output voltage
The output voltage is calculated by the following equation.
Vo = VINVthï½¥(R1+R2)/R2 [V]
R1,R2 : Resistor divider network
VINth : Error amp threshold voltage (typ.1V)
(but Vo<VINï½¥5 because of MAXDUTY Min=80%)
(7) CTL/SS setting the soft start time
The time after CTL/SS is released before the output voltage starts to rise.
t(start) = CCTLï½¥(VDo-Voff)/Iss [S]
approximated equation
The time after the output voltage starts up before it reaches the specified output level.
t(soft) = CCTLï½¥(VDUTY-VDo)/Iss [S] approximated equation
VDUTY = VDo+0.5ï½¥(1-VIN/VOUT) [V]
CCTL : CTL/SS–GND capacitande Vdo : 0% duty threshold (Typ 1.6V) Voff : Output off CTL/SS voltage
Iss : CTL/SS charge current (Typ 1uA) VDUTY : stabilization operating ON duty.
●Timing chart
Dead-time setting
voltage
Stand-by threshold
voltage
Oscillator output
FB terminal voltage
CTL/SS terminal voltage
t(start)
Output waveform
t(soft)
ON/OFF
VDUTY
Fig.9
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2009.05 - Rev.A