FAN8048 查看數據表（PDF） - Fairchild Semiconductor
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FAN8048 Datasheet PDF : 34 Pages
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FAN8048
3. DC-DC Converter (VG Converter and Synchronous DC-DC Converter)
3-1. VG Converter (Step up Converter)
The VG converter is used to generate necessary power (VG) for upper side output power switches operation of 4 channels H-
bridge driver and other internal circuit operations as shown in Figure 7. The output voltage (VG) of VG converter is internally
set to 7.0V, and it activates DC-DC Converter 1 when VG converter output voltage reaches 3.9 V. Also VG converter has an
oscillator function, which is required for switching operations and to minimize external components.
LG
D1
VBAT
LG
48
DC-DC Converter
Wake-up Singnal
SW
VG
1
Vref1
R1
R2
CG
FAN8048
Sawtooth
Clock
4 SYSTEM_ON
ON
Figure 7. Set up Converter (VG Converter)
3-2. Synchronous Step-up/Down Converter
The FAN8048 provides high efficiency and low noise power for applications such as portable instrumentation. Figure 8 shows
the functional block diagram of synchronous step up/down converter.
DSW
19
USW
21
18
VBAT
VA
VB
Power Stage
PCT
7
CLK 8
Sync. Clock
VD
VA
VB
VC
VC
VD
PCT
OSC2
VSYS
22
Start Comp
1.79V
SPRT
5
Stop Comp
0.5V
VCOM
1.27V
Start & Short Circuit Protection
CP
VZ1
VX
10
R1
Error Amp
RC
CC
11
VZ2
VY
0.9V
R2
0.56V
OSC2
PCT
VSYS
1.48V
SOFT
9
VCOM
FAN8048 DC-DC Converter
Figure 8. Block diagram of Step-up/down converter
In Figure 8, the output voltage (VSYS) of DC-DC converter is calculated as follows:
VSYS
= VREF
× (1+
R1 )
R2
[V ]
where, VREF = 0.9[V ]
14
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