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| 型号： | MAX8717ETI+T |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 21/30页 |
| 文件大小： | 0K |
| 描述： | IC CNTRLR PWR SUP 28-TQFN |
| 标准包装： | 2,500 |
| 应用： | 控制器，笔记本电脑电源系统 |
| 输入电压： | 4 V ~ 26 V |
| 输出数： | 2 |
| 输出电压： | 3.3V，5V，1 V ~ 5.5 V |
| 工作温度： | 0°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 28-WFQFN 裸露焊盘 |
| 供应商设备封装： | 28-TQFN-EP（5x5） |
| 包装： | 带卷 (TR) |
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Interleaved High-Efficiency, Dual Power-Supply
Controllers for Notebook Computers
Output Undervoltage Protection
If the output voltage of either SMPS falls below 70% of
its regulation voltage, the corresponding controller sets
its undervoltage fault latch, pulls PGOOD_ low, and
begins soft-shutdown for the corresponding SMPS con-
troller by pulsing DL_. DH_ remains off during the soft-
shutdown sequence initiated by an unvervoltage fault.
The other controller is not affected. After soft-shutdown
has completed, the MAX8716/MAX8717/MAX8756/
MAX8757 force DL_ high and DH_ low. Cycle V CC
below 1V or toggle ON_ to clear the undervoltage fault
latch and restart the SMPS controller.
V CC POR and UVLO
Power-on reset (POR) occurs when V CC rises above
approximately 2V, resetting the fault latch and prepar-
ing the PWM for operation. V CC undervoltage-lockout
(UVLO) circuitry inhibits switching, forces PGOOD_
low, and forces the DL_ gate drivers low.
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?
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Maximum Load Current. There are two values to
consider. The peak load current (I LOAD(MAX) ) deter-
mines the instantaneous component stresses and fil-
tering requirements and thus drives output capacitor
selection, inductor saturation rating, and the design
of the current-limit circuit. The continuous load cur-
rent (I LOAD ) determines the thermal stresses and thus
drives the selection of input capacitors, MOSFETs,
and other critical heat-contributing components.
Switching Frequency. This choice determines the
basic trade-off between size and efficiency. The
optimal frequency is largely a function of maximum
input voltage, due to MOSFET switching losses that
are proportional to frequency and V IN 2 . The opti-
mum frequency is also a moving target, due to rapid
improvements in MOSFET technology that are mak-
ing higher frequencies more practical.
Inductor Operating Point. This choice provides
If V CC drops low enough to trip the UVLO comparator
while ON_ is high, the MAX8716/MAX8717/MAX8756/
MAX8757 immediately force DH_ and DL_ low on both
controllers. The output discharges to 0V at a rate
dependent on the load and the total output capaci-
tance. This prevents negative output voltages, eliminat-
ing the need for a Schottky diode to GND at the output.
Thermal Fault Protection
The MAX8716/MAX8717/MAX8756/MAX8757 feature a
thermal fault-protection circuit. When the junction tem-
perature rises above +160°C, a thermal sensor sets the
fault latches, pulls PGOOD low, and shuts down both
SMPS controllers using the soft-shutdown sequence
(see the Sort-Start and Soft-Shutdown section). Cycle
V CC below 1V or toggle ON1 and ON2 to clear the fault
latches and restart the controllers after the junction
temperature cools by 15°C.
trade-offs between size vs. efficiency and transient
response vs. output ripple. Low inductor values pro-
vide better transient response and smaller physical
size, but also result in lower efficiency and higher
output ripple due to increased ripple currents. The
minimum practical inductor value is one that causes
the circuit to operate at the edge of critical conduc-
tion (where the inductor current just touches zero
with every cycle at maximum load). Inductor values
lower than this grant no further size-reduction bene-
fit. The optimum operating point is usually found
between 20% and 50% ripple current. When pulse-
skipping ( SKIP low and light loads), the inductor
value also determines the load-current value at
which PFM/PWM switchover occurs.
Inductor Selection
The switching frequency and inductor operating point
determine the inductor value as follows:
Design Procedure
Firmly establish the input voltage range and maximum
load current before choosing a switching frequency
and inductor operating point (ripple-current ratio). The
L =
V OUT ( V IN ? V OUT )
V IN ? OSC I LOAD ( MAX ) LIR
primary design trade-off lies in choosing a good switch-
ing frequency and inductor operating point, and the fol-
lowing four factors dictate the rest of the design:
For example: I LOAD(MAX) = 5A, V IN = 12V, V OUT = 5V,
f OSC = 300kHz, 30% ripple current or LIR = 0.3:
?
Input Voltage Range. The maximum value (V IN(MAX) )
must accommodate the worst-case, high AC-adapter
L =
5 V × ( 12 V ? 5 V )
12 V × 300 kHz × 5 A × 0 . 3
= 6 . 50 μ H
voltage. The minimum value (V IN(MIN) ) must account
for the lowest battery voltage after drops due to con-
nectors, fuses, and battery selector switches. If there
is a choice at all, lower input voltages result in better
efficiency.
Find a low-loss inductor having the lowest possible DC
resistance that fits in the allotted dimensions. Most
inductor manufacturers provide inductors in standard
values, such as 1.0μH, 1.5μH, 2.2μH, 3.3μH, etc. Also
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| MAX8718ETA-T | 功能描述:低压差稳压器 - LDO RoHS:否 制造商:Texas Instruments 最大输入电压:36 V 输出电压:1.4 V to 20.5 V 回动电压（最大值）:307 mV 输出电流:1 A 负载调节:0.3 % 输出端数量: 输出类型:Fixed 最大工作温度:+ 125 C 安装风格:SMD/SMT 封装 / 箱体:VQFN-20 |
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