参数资料
型号: MAX15023ETG/V+T
厂商: Maxim Integrated Products
文件页数: 17/28页
文件大小: 0K
描述: IC REG CTRLR BUCK PWM VM 24WQFN
产品培训模块: Lead (SnPb) Finish for COTS
Obsolescence Mitigation Program
标准包装: 2,500
PWM 型: 电压模式
输出数: 2
频率 - 最大: 1MHz
占空比: 87.5%
电源电压: 4.5 V ~ 28 V
降压:
升压:
回扫:
反相:
倍增器:
除法器:
Cuk:
隔离:
工作温度: -40°C ~ 85°C
封装/外壳: 24-WFQFN 裸露焊盘
包装: 带卷 (TR)
MAX15023
Wide 4.5V to 28V Input, Dual-Output
Synchronous Buck Controller
R 1 2 ? ?
? ? 1 ?
? ? V OUT _ ? ?
Setting the Output Voltage
Set the MAX15023 output voltage on each channel by
connecting a resistive divider from the output to FB_ to
SGND (Figure 3). Select R 2 (FB_ to SGND resistor) less
than or equal to 16k ? . Calculate R 1 (OUT_ to FB_ resis-
tor) with the following equation:
= R
? ?
? ? V FB _ ? ?
where V FB_ = 0.6V (typ) (see the Electrical Characteristics
Inductor Selection
Three key inductor parameters must be specified for
operation with the MAX15023: inductance value (L),
inductor saturation current (I SAT ), and DC resistance
(R DC ). To select inductance value, the ratio of inductor
peak-to-peak AC current to DC average current (LIR)
must be selected first. A good compromise between
size and loss is a 30% peak-to-peak ripple current to
average-current ratio (LIR = 0.3). The switching fre-
quency, input voltage, output voltage, and selected LIR
then determine the inductor value as follows:
L = OUT IN OUT
table) and V OUT_ can range from 0.6V to (0.85 x V IN ).
Resistor R 1 also plays a role in the design of the Type
III compensation network. If a Type III compensation
V ( V ? V
V IN f SW I OUT LIR
)
network is used, make sure to review the values of R 1
and R 2 according to the Type III Compensation
Network (See Figure 5) section.
Setting the Switching Frequency
The switching frequency, f SW , for each channel is set
by a resistor (R T ) connected from RT to SGND. The
relationship between f SW and R T is:
where V IN , V OUT , and I OUT are typical values (so that
efficiency is optimum for typical conditions). The
switching frequency is set by R T (see the Setting the
Switching Frequency section). The exact inductor value
is not critical and can be adjusted in order to make
trade-offs among size, cost, efficiency, and transient
response requirements. Lower inductor values minimize
size and cost, but also improve transient response and
R T =
24806
( f SW ) 1 . 0663
reduce efficiency due to higher peak currents. On the
other hand, higher inductance increases efficiency by
reducing the RMS current, but requires more output
where f SW is in kHz, R T is in k ? , and 24806 is in
1/farad. For example, a 600kHz switching frequency is
set with R T = 27.05k ? . Higher frequencies allow
designs with lower inductor values and less output
capacitance. Consequently, peak currents and I 2 R
losses are lower at higher switching frequencies, but
core losses, gate-charge currents, and switching loss-
es increase.
OUT_
capacitance to meet load-transient specifications.
Find a low-loss inductor having the lowest possible DC
resistance that fits in the allotted dimensions. The
inductor’s saturation rating (I SAT ) must be high enough
to ensure that saturation can occur only above the max-
imum current-limit value, given the tolerance of the low-
side MOSFET’s on-resistance and of the LIM_ reference
current (I LIM ). On the other hand, these tolerances
should not prevent the converter from delivering the
rated load current (I LOAD(MAX) ). Combining these con-
ditions, the inductor saturation current (I SAT ) should be
such that:
× ? 1 +
? × I LOAD(MAX)
R 1
I SAT >
RDS(ON,MAX)
RDS(ON,TYP)
?
?
LIR ?
2 ?
FB_
where R DS(ON,MAX) and R DS(ON,TYP) are the maximum
MA15023
Figure 3. Adjustable Output Voltage
Maxim Integrated
R 2
and typical on-resistance of the low-side MOSFET. For
a given inductor type and value, choose the LIR corre-
sponding to the worst-case inductor tolerance.
For LIR = 0.4, and a +25% on the low-side MOSFET’s
R DS(ON,MAX) , the inductor saturation current should be
about 50% greater than the converter’s maximum load
current. A variety of inductors from different manufac-
turers can be chosen to meet this requirement (for
example, Coilcraft MSS1278 series).
17
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