FAN8048 データシートの表示（PDF） - Fairchild Semiconductor

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FAN8048

2 DC-DC Converter & 4-CH PWM Motor IC

Fairchild Semiconductor 

FAN8048

3-7. Operation mode of Step-up/down converter

Figure 9 shows the connection of the four internal output power switches, external Inductor, and input/output voltage, which

are components of the FAN8048 built-in DC-DC converter.

As shown in Figure 10, the DC-DC converter determines a switching operation mode (Buck, Buck-Boost and Boost) according

to the relationship between control voltage VX and VY and oscillator output voltage VPCT. Also, the DC-DC converter indi-

cates the different operational statuses of output power switch (Output switches, A, B, C, and D) according to operational

mode. Herein, control voltage VX is the output voltage of error amplifier, and voltage VY is level shift voltage in VX.

VIN DSW

18

19

A

VA

USW VSYS

21

22

D

VD

VB

B

VC

C

Figure 9. Simplified Diagram of Output Swiches

75%

DMAX_BOOST

Switch A ON B OFF

PWM CD Swiches

Boost Mode

DMIN_BOOST

Four Switches PWM

DMAX_BUCK

Buck/Boost Mode

Switch D ON C OFF

PWM AB Swiches

Buck Mode

VX > VPCT

VX > VY

VX ≤ VPCT

VY ≤ VPCT

VY > VPCT

VY > VX

0%

Duty

Figure 10. Switching control vs. internal control voltages, VX and VY

16

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