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参数资料
| 型号： | APW7077ZBI-TUL |
| 厂商： | Anpec Electronics Corporation |
| 元件分类： | DC/DC变换器 |
| 英文描述： | PWM Step-Up DC-DC Converter |
| 中文描述： | PWM升压型DC - DC转换器 |
| 文件页数： | 14/21页 |
| 文件大小： | 444K |
| 代理商： | APW7077ZBI-TUL |
Copyright
ANPEC Electronics Corp.
Rev. A.4 - S ep, 2005
APW 7077/ A
www.anpec.com.tw
14
Function Description ( Cont.)
Inductor Selection (Cont.)
OUT
O
I
OUT
V
fsw
D
(max)
×
(min)
C
×
=
The ESR is also important because it determines the
peak to peak output voltage ripple according to the
approximate equation:
With 1% output voltage ripple, low ESR capacitor
should be used to reduce output ripple voltage. In
general, a 100uF to 220uF low ESR (0.10
to 0.30
)
Tantalum capacitor should be appropriate. The choice
of output capacitors is also somewhat arbitrary and
depends on the design requirements for output voltage
ripple. A minimum value of 10μF is recommended and
may be increased to a larger value.
Input Capacitor
The input capacitor can stabilize the input voltage and
minimize peak current ripple from the source. The size
used is dependant on the application and board layout.
ESR
I
V
L
IN
×
=
O
I
OUT
V
ESR
=
when
I
L
is less than the average inductor current.
Care must be taken to make sure that the switch will
not reach its current limit during normal operation.
The inductor must also be sized accordingly. It should
have a saturation current rating higher than the peak
inductor current expected. The output voltage ripple is
also affected by the total ripple current.
Output Capacitor
The output capacitor is used for sustaining the output
voltage when the external MOSFET or bipolar
transistor is switched on and smoothing the ripple
voltage.
The output capacitance needed is calculated in
equations.
If the regulator will be loaded uniformly, with very little
load changes, and at lower current outputs, the input
capacitor size can often be reduced. The size can also
be reduced if the input of the regulator is very close to
the source output. The size will generally need to be
larger for applications where the regulator is supplying
nearly the maximum rated output or if large load steps
are expected. A minimum value of 10μF should be
used for the less stressful conditions while a 22μF to
47μF capacitor may be required for higher power and
dynamic loads. Small ESR Tantalum or ceramic ca-
pacitor should be suitable and the total input ripple
voltage can be calculated
Design Example
It is supposed that a step–up DC–DC controller with
3.3 V output delivering a maximum 1000 mA output
current with 100 mV output ripple voltage powering
from a 2.4 V input is to be designed.
Design parameters:
V
IN
= 2.4 V
V
OUT
= 3.3 V
I
O
= 1.0 A
V
OUT
= 100 mV
fsw= 300 kHZ
Ratio = 0.2 (typical for small output ripple voltage)
Assume the diode forward voltage and the transistor
saturation voltage are both 0.3V. Determine the maxi-
mum steady state duty cycle at V
IN
= 2.4 V:
D=0.273
Calculate the maximum inductance value which can
generate the desired current output and the preferred
delta inductor current to average inductor current ratio:
L=10uH
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