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| 型号： | ZL2106EVAL1Z |
| 厂商： | Intersil |
| 文件页数： | 17/29页 |
| 文件大小： | 0K |
| 描述： | BOARD EVAL STEP-DOWN ZL2106 |
| 标准包装： | 1 |
| 系列： | Zilker Labs™ |
| 主要目的： | DC/DC，步降 |
| 输出及类型： | 1，非隔离 |
| 输出电压： | 3.3V |
| 电流 - 输出： | 6A |
| 输入电压： | 12V |
| 稳压器拓扑结构： | 降压 |
| 频率 - 开关： | 400kHz |
| 板类型： | 完全填充 |
| 已供物品： | 板 |
| 已用 IC / 零件： | ZL2106 |
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ZL2106
I opp = I ostep
V OUT × ? ? 1 ? OUT
? ?
?
?
V INM
C OUT =
V orip
8 × f sw ×
ESR =
V orip
between output ripple and optimal load transient performance. A
good starting point is to select the output inductor ripple equal to
the expected load transient step magnitude (I ostep ):
(EQ. 2)
Now the output inductance can be calculated using Equation 3,
where V INM is the maximum input voltage:
? V ?
(EQ. 3)
L OUT =
fsw × I opp
The average inductor current is equal to the maximum output
current. The peak inductor current (I Lpk ) is calculated using
Equation 4 where I OUT is the maximum output current:
As a starting point, apportion one-half of the output ripple
voltage to the capacitor ESR and the other half to capacitance, as
shown in Equations 7 and 8:
I opp
(EQ. 7)
2
(EQ. 8)
2 × I opp
Use these values to make an initial capacitor selection, using a
single capacitor or several capacitors in parallel.
After a capacitor has been selected, the resulting output voltage
ripple can be calculated using Equation 9:
I Lpk = I OUT +
I opp
2
(EQ. 4)
V orip = I opp × ESR +
I opp
8 × f sw × C OUT
(EQ. 9)
P LDCR = DCR × I Lrms
(EQ. 5)
I CINrms = I OUT × D × ( 1 ? D )
Select an inductor rated for the average DC current with a peak
current rating above the peak current computed in Equation 4.
In overcurrent or short-circuit conditions, the inductor may have
currents greater than 2X the normal maximum rated output
current. It is desirable to use an inductor that still provides some
inductance to protect the load and the internal MOSFETs from
damaging currents in this situation.
Once an inductor is selected, the DCR and core losses in the
inductor are calculated. Use the DCR specified in the inductor
manufacturer’s data sheet.
2
Because each part of this equation was made to be less than or
equal to half of the allowed output ripple voltage, the V orip should
be less than the desired maximum output ripple.
INPUT CAPACITOR
It is highly recommended that dedicated input capacitors be
used in any point-of-load design, even when the supply is
powered from a heavily filtered 5V or 12V “bulk” supply from an
off-line power supply. This is because of the high RMS ripple
current that is drawn by the buck converter topology. This ripple
(I CINrms ) can be determined from Equation 10:
(EQ. 10)
( I )
I Lrms = I OUT +
I Lrms is given by Equation 6:
2 opp
12
2
(EQ. 6)
Without capacitive filtering near the power supply circuit, this
current would flow through the supply bus and return planes,
coupling noise into other system circuitry. The input capacitors
should be rated at 1.2X the ripple current calculated in Equation
10 to avoid overheating of the capacitors due to the high ripple
where I OUT is the maximum output current. Next, calculate the
core loss of the selected inductor. Since this calculation is
specific to each inductor and manufacturer, refer to the chosen
inductor data sheet. Add the core loss and the DCR loss and
compare the total loss to the maximum power dissipation
recommendation in the inductor data sheet.
OUTPUT CAPACITOR SELECTION
Several trade-offs must also be considered when selecting an
output capacitor. Low ESR values are needed to have a small
output deviation during transient load steps (V osag ) and low
output voltage ripple (V orip ). However, capacitors with low ESR,
such as semi-stable (X5R and X7R) dielectric ceramic capacitors,
also have relatively low capacitance values. Many designs can
use a combination of high capacitance devices and low ESR
devices in parallel.
For high ripple currents, a low capacitance value can cause a
significant amount of output voltage ripple. Likewise, in high
transient load steps, a relatively large amount of capacitance is
needed to minimize the output voltage deviation while the
inductor current ramps up or down to the new steady state
output current value.
17
current, which can cause premature failure. Ceramic capacitors
with X7R or X5R dielectric with low ESR and 1.1X the maximum
expected input voltage are recommended.
BOOTSTRAP CAPACITOR SELECTION
The high-side driver boost circuit utilizes an internal Schottky
diode (D B ) and an external bootstrap capacitor (C B ) to supply
sufficient gate drive for the high-side MOSFET driver. C B should
be a 47nF ceramic type rated for at least 10V.
C V2P5 SELECTION
This capacitor is used to both stabilize and provide noise filtering
for the 2.5V internal power supply. It should be between 4.7μF
and 10μF, should use a semi-stable X5R or X7R dielectric
ceramic with a low ESR (less than 10m Ω ) and should have a
rating of 4V or more.
C VR SELECTION
This capacitor is used to both stabilize and provide noise filtering
for the 7V reference supply. It should be between 4.7μF and
10μF, should use a semi-stable X5R or X7R dielectric ceramic
capacitor with a low ESR (less than 10m Ω ) and should have a
rating of 10V or more. Because the current for the bootstrap
supply is drawn from this capacitor, C VR should be sized at least
FN6852.6
February 20, 2013
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