BD8150KVT ROHM Co. Ltd., BD8150KVT Datasheet - Page 8

• Manufacturer Part Number: BD8150KVT
• Description: System Power Supplies Power Suuply Ic Series For Tft-lcd Panels
• Manufacturer: ROHM Co. Ltd.

Selecting Application Components
1 DC/DC converter block design
Each
output
voltage
•When short protection is triggered
1-1 Operating mode determination
1-2 Setting the oscillating frequency
1-3 L and C selection
1-4 Switching MOSFET selection
1-5 Rectification diode selection
5 V
Vcc
SCP
The step-down, step-up, and inverting switching regulators are comprised of UDSEL (Pins 58, 59), error amp input
NON (Pin 43), and INV pins (Pins 44, 53). NON1 is internally connected to BG.
Applying capacitance to the CT pin (Pin 32) allows the oscillating frequency
to be set. Refer to Fig.1 when setting the capacitance. When nothing is
applied, the frequency is set to 1 MHz (Typ.).
Select the output L and C so that the output ripple voltage is within specifications. Select L so that the sum of the
ripple current and load current (input current for step-up and inversion) does not exceed the rated current of the coil.
And select C so that the output ripple voltage including the switching noise does not exceed breakdown voltage.
There is no problem if the absolute maximum rating exceeds the rated current of L and the breakdown voltage +
rectification diode VF for C, but select a low gate capacitance (inrush charge amount) to achieve high-speed switching.
Select a Schottky barrier diode having a current capacity above the rated current of L and an inverse breakdown
voltage above the breakdown voltage of C and that, in particular, has a low forward direction voltage VF.
1.25 V
3.3 V
23 V
10 V
-6 V
Coil current
Output ripple voltage
Step-down
Step-up
Inverting
Operating
mode
∆IL = V
∆IL = V
∆IL = (V
∆VPP = (∆IL + IO) × RESR + (ΔIL × VO) / (2 × C × f × V
Where, RESR = Internal resistance component in output C.
CC
CC
× (VO − V
× VO / (L × f × (VO − V
UDSEL
GND
V
V
CC
CC
CC
∆VPP = ∆IL × RESR + (∆IL × VO) / (2 × C × f × V
− VO) × VO / (L × f × V
CC
Fig. 21 During Short Protection Operation
) / (L × f × VO) [A] (Step-up)
FEEDBACK
NON
BG
BG
CC
)) [A] (Inversion)
8/16
CC
) [A] (step-down)
FEEDBACK
FEEDBACK
GND
INV
Fig. 22 CT Capacitance vs Oscillating Frequency
CC
) [V] (Step-up, Inversion)
CC
10000
) [V] (step-down)
1000
100
10
1
10
CCT [pF]
100
1000