R1280D002X Datasheet, PDF (25/26 Pages) RICOH electronics devices division – 2CH PWM DC/DC Controller

q R1280D002B
C10
VOUT1
VOUT3
C11
L1
C1
R1
R2
C3
C6 ^NMOS
EXT1 EXT2
GND ^VIN
CE
Vrefout
R5
C4
DTC1 DTC2
C5
PMOS
C8
L2
R3
V_FB1 V_FB2
Diode
C7
R4
VOUT2
R6
External Components
Inductor L1,2: 6.8µH, LDR655312T(TDK)
Diode: FS1J3 (Origin Electronics)
NMOS: IR7601 (International Rectifier)
PMOS: Si3443 (Siliconix)
Resistors: R1, R2, R3, R4 for Setting Output Voltage. Recommendation values are R1+R2≤100kΩ or R3+R4≤100kΩ
R5=43kΩ, R6=10kΩ
Capacitors: Ceramic Capacitor
(Example)
R1280D002B: C1=C2=10µF, C3=4.7µF, C4=0.33µF, 5=0.33µF, C6=120pF,C7=50pF,C8=C10=C11=1µF
This IC can be used 3 Output TFT Bias Circuit as shown above. VOUT3=2×VOUT1-Vf
Note: Maximum voltage tolerance of each component should be considered. With the transistor shown above is
appropriate to set up to +15V as VOUT1, -15V as VOUT2, 30V as VOUT3
s EXTERNAL COMPONENTS
1. How to set the output voltages
As for step-up side, feedback (VFB1) pin voltage is controlled to maintain 1V, therefore,
VOUT1: R1+R2=VFB1: R2
Thus, VOUT1=VFB1×(R1+R2)/R2
Output Voltage is adjustable with R1 and R2.
As for inverting side, Feedback (VFB2) pin voltage is controlled to maintain 0V, therefore,
Vrefout : R3=|-VOUT2|:R4
Thus, |-VOUT2|=Vrefout×R4/R3
Output Voltage is adjustable with R3 and R4.
2. How to set Soft Starting Time
As for R1280D002B, soft start time is adjustable with connecting a capacitor to DTC pin.
Soft starting time, TSS1 and TSS2 are adjustable. Soft starting time can be set with the time constant of RC.
Soft starting time can be described as in next formula. (Topt=25°C)
TSS1≅RS1×C4, TSS2≅RS2×C5
In the above formulas, RS1 value is TYP. 32kΩ, while RS2 value is TYP. 45kΩ. Tolerance of these values is ±25%
caused by dispersion of wafer process parameters.
On the other hand, as for R1280D002A/C, each soft start time is set with the time constant of each external resistor
Rev. 1.10
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