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

1-4. Power-On Reset (POR) Function

FAN8048 has two DC-DC converters to supply stable power to external circuits and components of the CD player set.

Therefore, for these output voltages of DC-DC converters to provide stable power to external circuits and their components,

the DC input voltage,VIN, and the output voltages of converter, VSYS1 and VSYS2, monitoring function is required.

The DC input voltage, VIN, and the output voltage of converter2 are individually divided by the internal resistors and then

compared with the internal 0.5V reference voltage, VREF2, to determine the low voltages condition.

This power on reset (POR) circuit is shown in Figure2.

VSYS2 14

VIN 18

VSYS1

VSYS1 22

Vref2

2 RST

RST

Figure 2. Block Diagram of Power On Reset

1-5. Power Sequence

The following graph and flowchart of Figure 3 and Figure 4 show the power sequence of the VG converter and two DC-DC

converters (DC-DC converter1 and DC-DC Converter2); herein, VG converter generates power for internal circuits and upper

side output power switches of the 4 channels H-bridge driver, and the DC-DC converters supply the external circuits and com-

ponents.

Voltage

VG=7.0V

3.9V

1.35V

Hysteresis

Converter 1 Converter 2 Reset Signal

Wake-up Wake-up

Figure 3. Plot of Power Sequence

VSYS1

VRST

VSYS2

t

11

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