FA7703 Datasheet, PDF (19/21 Pages) Fuji Electric – FUJI Power Supply Control IC

FA7703/04
FA7703/7704
(11)Setting of the output voltage of DC-DC
converter
Figure 13 shows the ways to set each channel
of the output voltage of DC-DC converter. The
precision of output voltage based on
FA7703/04’s characteristics depends on the
variation of the voltage of VB (±2%) and VREF
(±1%), and also on offset voltage, and
temperature characteristics.
Ch1:Buck(FA7703/04)
Vout1
11
R1
SEL1
13
-
IN1-
12
R2
+
FB1
VB
(1.0V)
7
10
OUT1
Vout1
selection Guide
FA7703 ^{Ch1 Buck, Boost, Fly-back}
Ch2 Buck, Inverting (Pch driven)
FA7704 ^{Ch1 Buck, Boost, Fly-back}
Ch2 Boost, Fly-back (Nch driven)
If using FA7703/04, and building:
In the case of a boost, a buck, or a fly-back circuit
in ch1, the output voltage can be calculated with:
Vout1 = ^{R1+ R2} ×VB
R2
If using FA7703, and building:
A buck circuit in ch2, the output voltage can be
calculated with:
Vout2 = ^{R3 + R4} ×VREF
R3
A inverting circuit in ch2, the output voltage can
be calculated
with the following formula. (the output voltage is
negative.)
Vout 2
=
R3 + R4
R3
×V1−
R4
R3
× V_REF
,where
V1 =
R8
R7 + R8
× V_REF
The ratio of resistance can be calculated with:
R3 ₌ V_REF − V1
R4 Vout2 + V1
(Use the absolute value of Vout2 voltage)
If setting R7=R8, then,
Vout2
=
V_REF
×
⎜⎛
⎝
R3 − R4
2R3
⎟⎞
⎠
If using FA7704, and building:
A boost, or fly-back circuit in ch2, the output
voltage can be calculated with:
Vout 2
=
R3 + R4
R3
× V_REF
Ch1:Boost(FA7703/04)
Vout1
16
11
R1
REG SEL1
13
IN1-
R2
-
12
+
FB1
VB
(1.0V)
10
OUT1
7
Vout1
Ch2:Buck(FA7703)
Vout2
R4
R3
5
IN2-
4
IN2+
14
REF
-
6
+
FB2
OUT2 ⁸
7
Vout2
Ch2:Inverting(FA7703)
R3
R7
4
IN2+
R4
V1 5
IN2-
Vout2 ^R8
14
REF
+
6
-
FB2
8
OUT2
7
Vout2
Ch2:Boost(FA7704)
Vout2
R4
R3
5
IN2-
4
IN2+
14
REF
-
6
+
FB2
OUT2 8
7
Vout2
Fig.13
Please note that DO NOT leave SEL1 terminal
open in operation, and be sure to connect it to
GND or VREG terminal.
Fuji Electric Systems Co., Ltd.
AN-057E Rev.1.0
Jun-2010
19
http://www.fujielectric.co.jp/fdt/scd/