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| 型号： | MAX5073ETI+T |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 16/25页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK BST ADJ 1A/2A 28TQFN |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 2,500 |
| 类型： | 降压（降压），升压（升压） |
| 输出类型： | 可调式 |
| 输出数： | 2 |
| 输出电压： | 0.8 V ~ 28 V |
| 输入电压： | 4.5 V ~ 23 V |
| PWM 型： | 电压模式 |
| 频率 - 开关： | 200kHz ~ 2.2MHz |
| 电流 - 输出： | 1A，2A |
| 同步整流器： | 无 |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 28-WFQFN 裸露焊盘 |
| 包装： | 带卷 (TR) |
| 供应商设备封装： | 28-TQFN-EP（5x5） |
2.2MHz, Dual-Output Buck or Boost Converter
with Internal Power MOSFETs
Inductor Selection
Three key inductor parameters must be specified for
operation with the MAX5073: inductance value (L), peak
inductor current (I L ), and inductor saturation current
(I SAT ). The minimum required inductance is a function of
operating frequency, input-to-output voltage differential
and the peak-to-peak inductor current ( ? I L ). Higher ? I L
allows for a lower inductor value while a lower ? I L
requires a higher inductor value. A lower inductor value
minimizes size and cost, improves large-signal transient
response, but reduces efficiency due to higher peak cur-
rents and higher peak-to-peak output ripple voltage for
the same output capacitor. On the other hand, higher
inductance increases efficiency by reducing the ripple
current. However, resistive losses due to extra wire turns
can exceed the benefit gained from lower ripple current
The input ripple waveform would be unsymmetrical due
to the difference in load current and duty cycle
between converter 1 and converter 2. The input ripple
is comprised of ? V Q (caused by the capacitor dis-
charge) and ? V ESR (caused by the ESR of the capaci-
tor). A higher load converter dictates the ESR
requirement, while the capacitance requirement is a
function of the loading mismatch between the two con-
verters. The worst-case mismatch is when one converter
is at full load while the other is at no load or in shutdown.
Use low-ESR ceramic capacitors with high ripple-cur-
rent capability at the input. Assume the contribution
from the ESR and capacitor discharge equal to 50%.
Calculate the input capacitance and ESR required for a
specified ripple using the following equations:
? I OUT +
2 ?
?
levels, especially when the inductance is increased with-
out also allowing for larger inductor dimensions. A good
compromise is to choose ? I L equal to 30% of the full load
current. To calculate the inductance use the following
equation:
where
ESR IN =
? V ESR
? ? I L ?
?
L =
V OUT ( V IN ? V OUT )
V IN × f SW × ? I L
? I L =
( V IN ? V OUT ) × V OUT
V IN × f SW × L
where V IN and V OUT are typical values (so that efficien-
cy is optimum for typical conditions). The switching fre-
and
quency is set by R OSC (see the Setting the Switching
Frequency section). The peak-to-peak inductor current,
which reflects the peak-to-peak output ripple, is worse
at the maximum input voltage. See the Output Capacitor
Selection section to verify that the worst-case output rip-
ple is acceptable. The inductor saturating current is also
where
C IN =
I OUT × D ( 1 ? D )
? V Q × f SW
D = OUT
important to avoid runaway current during output over-
load and continuous short circuit. Select the I SAT to be
higher than the maximum peak current limits of 4.5A
and 2.2A for converter 1 and converter 2.
Input Capacitors
The discontinuous input current waveform of the buck
converter causes large ripple currents at the input. The
switching frequency, peak inductor current, and the
allowable peak-to-peak voltage ripple dictate the input
capacitance requirement. Increasing the switching fre-
quency or the inductor value lowers the peak to aver-
age current ratio, yielding a lower input capacitance
requirement. Note that two converters of MAX5073 run
180° out-of-phase, thereby effectively doubling the
switching frequency at the input.
V
V IN
where I OUT is the maximum output current from either
converter 1 or converter 2, and D is the duty cycle for
that converter. f SW is the frequency of each individual
converter. For example, at V IN = 12V, V OUT = 3.3V at
I OUT = 2A, and with L = 3.3μH, the ESR and input
capacitance are calculated for a peak-to-peak input
ripple of 100mV or less, yielding an ESR and capaci-
tance value of 20m ? and 6.8μF for 1.25MHz frequency.
Use a 100μF capacitor at low input voltages to avoid
possible undershoot below the undervoltage lockout
threshold during power-on and transient loading.
16
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