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参数资料
| 型号： | XRP7665EVB |
| 厂商： | Exar Corporation |
| 文件页数： | 8/12页 |
| 文件大小： | 0K |
| 描述： | BOARD EVAL STEP-DOWN XRP7665 |
| 标准包装： | 1 |
| 主要目的： | DC/DC，步降 |
| 输出及类型： | 1，非隔离 |
| 输出电压： | 0.925 V ~ 16 V |
| 电流 - 输出： | 3A |
| 输入电压： | 4.75 V ~ 18 V |
| 稳压器拓扑结构： | 降压 |
| 频率 - 开关： | 340kHz |
| 板类型： | 完全填充 |
| 已供物品： | 板 |
| 已用 IC / 零件： | XRP7665 |
| 其它名称： | 1016-1754 |
X R P 7 6 6 5
3 A 1 8 V S y n c h r o n o u s S t e p - D o w n C o n v e r t e r
OUTPUT INDUCTOR
Select the output inductor for inductance L, DC
current rating I DC and saturation current rating
I SAT . I DC should be larger than regulator output
current. I SAT , as a rule of thumb, should be
50% higher than the regulator output current.
Since the regulator is rated at 3A then I DC ≥ 3A
and I SAT ≥ 4.5A. Calculate the inductance from:
of thumb, should be at least twice the output
voltage. When calculating the required
capacitance, usually the overriding
requirement is current load-step transient. If
the unloading transient (i.e., when load
transitions from a high to a low current) is
met, then usually the loading transient (when
load transitions from a low to a high current)
is met as well. Therefore calculate the C OUT
based on the unloading transient requirement
from:
Where:
VOUT(V) ΔI L(p-p) (A)
L(μH)
ΔI L is peak-to-peak inductor current ripple
nominally set to 30%-40% of I OUT
f S is nominal switching frequency (340kHz)
As an example, inductor values for several
common output voltages are shown in tables 1
and 2. Note that example inductors shown in
tables 1 and 2 are Wurth shielded inductors. If
the target application is not sensitive to EMI
then unshielded inductors may be used.
Inductor
Example
5.0 0.9 10 744314101
3.3 0.7 10 744314101
2.5 0.6 10 744314101
1.8 0.6 7.6 744314760
1.5 0.5 7.6 744314760
1.2 0.6 4.9 744314490
Table 1: Suggested inductor values for V IN =12V and
I OUT =3A
Where:
L is the inductance calculated in the preceding
step
I High is the value of load-step prior to
unloading. This is nominally set equal to
regulator current rating (3A).
I Low is the value of load-step after unloading.
This is nominally set equal to 50% of regulator
current rating (1.5A).
V transient is the maximum permissible voltage
transient corresponding to the load step
mentioned above. V transient is typically specified
from 3% to 5% of V OUT .
ESR of the capacitor has to be selected such
that the output voltage ripple requirement
ΔV OUT , nominally 1% of V OUT , is met. Voltage
ripple ΔV OUT is mainly composed of two
components: the resistive ripple due to ESR
and capacitive ripple due to C OUT charge
transfer. For applications requiring low voltage
VOUT(V) ΔI L(p-p) (A)
L(μH)
Inductor
Example
ripple, ceramic capacitors are recommended
because of their low ESR which is typically in
3.3
2.5
1.8
1.5
1.2
0.7
0.8
0.7
0.6
0.5
4.9
4.9
4.9
4.9
4.9
744314490
744314490
744314490
744314490
744314490
the range of 5m? . Therefore ΔV OUT is mainly
capacitive. For ceramic capacitors calculate
the ΔV OUT from:
Table 2: Suggested inductor values for V IN =5V and
I OUT =3A
OUTPUT CAPACITOR C OUT
Select the output capacitor for voltage rating,
capacitance C OUT and Equivalent Series
Resistance ESR. The voltage rating, as a rule
Where:
ΔI L is from table 1 or 2
C OUT is the value calculated above
f s is nominal switching frequency (340kHz)
? 2013 Exar Corporation
8/12
Rev. 2.0.1
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