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PDF 71128 Data sheet ( Hoja de datos )
| Número de pieza | 71128 | |
| Descripción | Simple Solution for Dynamically Programming the Output Voltage of DC-DC Converters | |
| Fabricantes | Vishay Siliconix | |
| Logotipo |  |
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AN731
Vishay Siliconix
Simple Solution for Dynamically Programming the
Output Voltage of DC-DC Converters
INTRODUCTION
Figure 1 shows a typical dc-to-dc converter configuration. As in
many PWM controllers, the non-inverting input of the voltage
feedback error amplifier is internally connected to the
reference voltage, Vr. The output voltage of the converter is set
by a resistor divider network R1 and R2. This configuration
enables a fixed output voltage that is equal to or greater than
the reference voltage. But in many power conversion designs,
it is useful to vary the output to a value lower than the reference
voltage and to dynamically adjust the output voltage. The
op-amp circuit shown in Figure 3 gives designers a simple way
to do this. Scaling the output voltage with respect to a control
voltage VC is totally flexible. This application note describes
how to use this simple solution and provides a step-by-step
design procedure to assist designers in calculating the specific
parameters required by their circuits.
DESIGN REQUIREMENT
Reference voltage, Vr
Control voltage: VC = VC1 to VC2
Output voltage: VO = VO1 at VC = VC1, VO = VO2 at VC = VC2,
and VO is linear for any value of VC in its range.
These design requirements are shown in Figure 2. The output
voltage is a linear function with respect to the control voltage.
The function crosses two end points A = (VC1, VO1) and B =
(VC2, VO2).
VIN Power Stage
VOUT
PWM
–
+
EA
PWM Controller
FB
Vr
R1
R2
FIGURE 1. Typical DC/DC Converter Configuration
VO (V)
B (VC2, VO2)
A (VC1, VO1)
VC (V)
FIGURE 2. Output Voltage vs Control Voltage Requirement
VIN
Document Number: 71128
28-Jan-00
Power Stage
VOUT
PWM
–
+
EA
PWM Controller
FB
Vr
R1
A
R2
VX
R3
LM358
B
–
+ Vr2
R4
Op-Amp Circuit
FIGURE 3. Op-Amp Circuit Offers Programmable Output Function
VC
www.vishay.com S FaxBack 408-970-5600
1
1 page  
AN731
Vishay Siliconix
P1
1
VIN
2.7 – 6 V
P2
1
GND
C8
0.1 mF
C7
10 mF
JP1
Enable
Converter
Disable
VDD
JP2
PWM
–PSM
SYNC
+1.3 V
C5
0.1 mF
U1
1 NC
2 SD
3 PWM/PSM
4 VIN/OUT
5 VIN/OUT
6 VIN/OUT
7 SYNC
8 GND
9 VREF
10 FB
COIL
COIL
MODE
PGND
PGND
VS
VO
VDD
ROSC
COMP
20
19
18
17
16
15
14
13
12
11
Si9165
C1
100 pF
R6
3.9 kW
L1
1.5 mH
R4*
50 W
C4
220 pF
VDD
P3
VOUT
1
0.4 – 3.4 V
600 mA
Adjustable
R5
1 kW
C3
10 mF
P4
1
PGND
R1
22.1 kW
1%
C6
1 nF
R3
25 kW
C2
0.1 mF
R2
3.01 kW
1%
P5
VA
0.2 – 2.7 V
1
R8, 22.1 kW
R9, 390 W
VIN
R11
3.60 kW
U2A
-1
+
LM358D
R10
10 kW
VX
6 U2B
-7
5+
LM358D
C10
0.1 mF
NC
JP1: –SD to VIN for converter enable mode;
–SD to PGND for shutdown mode.
JP2: PWM/–PSM to VIN for PWM mode;
PWM/–PSM to PGND for PSM mode.
NOTE: VIN must be > VOUT +0.6 V for output regulation
* = Optional
Document Number: 71128
28-Jan-00
FIGURE 5. Schematic of Design Example, Using Si9165 Converter
www.vishay.com S FaxBack 408-970-5600
5
5 Page | ||
| Páginas | Total 7 Páginas | |
| PDF Descargar | [ Datasheet 71128.PDF ] | |
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