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| 型号： | MAX1993ETG+ |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 26/36页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 24-TQFN |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 75 |
| 系列： | Quick-PWM™ |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 600kHz |
| 占空比： | 100% |
| 电源电压： | 4.5 V ~ 5.5 V |
| 降压： | 是 |
| 升压： | 无 |
| 回扫： | 无 |
| 反相： | 无 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 无 |
| 工作温度： | -40°C ~ 85°C |
| 封装/外壳： | 24-WFQFN 裸露焊盘 |
| 包装： | 管件 |
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Quick-PWM Step-Down Controllers with Inductor
Saturation Protection and Dynamic Output Voltages
Design Procedure
Firmly establish the input voltage range and maximum
load current before choosing a switching frequency
Inductor Selection
The switching frequency and inductor operating point
determine the inductor value as follows:
and inductor operating point (ripple-current ratio). The
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:
L =
V OUT ( V IN ? V OUT )
V IN f SW I LOAD ( MAX ) LIR
? Input Voltage Range . The maximum value (V IN(MAX) )
must accommodate the worst-case, high AC-adapter
For example: I LOAD(MAX) = 5A, V IN = 12V, V OUT =
2.5V, f SW = 300kHz, 30% ripple current or LIR = 0.3
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
L =
2 . 5 V ( 12 V ? 2 . 5 )
12 V × 300 kHz × 5 A × 0 . 3
= 4 . 40 μ H
is a choice, lower input voltages result in better effi-
ciency.
? 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
Find a low-loss inductor having the lowest possible DC
resistance that fits in the allotted dimensions. Ferrite
cores are often the best choice, although powdered
iron is inexpensive and can work well at 200kHz. The
core must be large enough not to saturate at the peak
inductor current (I PEAK ):
I PEAK LOAD ( MAX ) ? 1 +
= I
?
of the current-limit circuit. The continuous load cur-
rent (I LOAD ) determines the thermal stresses and
thus drives the selection of input capacitors,
?
?
LIR ?
2 ?
MOSFETs, and other critical heat-contributing com-
ponents.
? 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 pro-
portional to frequency and V IN2 . The optimum fre-
quency 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
trade-offs: size vs. efficiency and transient response
vs. output ripple. Low inductor values provide better
transient response and smaller physical size but also
result in lower efficiency and higher output ripple
due to increased ripple currents. The minimum prac-
tical inductor value is one that causes the circuit to
Most inductor manufacturers provide inductors in stan-
dard values, such as 1.0μH, 1.5μH, 2.2μH, 3.3μH, etc.
Also look for nonstandard values, which can provide a
better compromise in LIR across the input voltage range.
If using a swinging inductor (where the no-load induc-
tance decreases linearly with increasing current), evalu-
ate the LIR with properly scaled inductance values.
Transient Response
The inductor ripple current also affects transient-
response performance, especially at low V IN - V OUT dif-
ferentials. Low inductor values allow the inductor
current to slew faster, replenishing charge removed
from the output filter capacitors by a sudden load step.
The output sag is also a function of the maximum duty
factor, which can be calculated from the on-time and
minimum off-time:
(
)
2 ? ? V OUT K ? ?
V IN ? ?
? ? ( V IN OUT ) K ?
2 C OUT OUT ? ? ? + t OFF ( MIN ) ?
? ? V IN ? ?
operate at the edge of critical conduction (where the
inductor current just touches zero with every cycle at
maximum load). Inductor values lower than this grant
no further size-reduction benefit. The optimum oper-
ating point is usually found between 20% and 50%
ripple current. When pulse skipping ( SKIP low and
light loads), the inductor value also determines the
V SAG =
L Δ I LOAD ( MAX ) ? ? + t OFF ( MIN ) ?
V
? ?
? ?
? ? ?
? V ?
load-current value at which PFM/PWM switchover
occurs.
where t OFF(MIN) is the minimum off-time (see the
Electrical Characteristics ) and K is from Table 3.
26
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相关代理商/技术参数 |
参数描述 |
|---|---|
| MAX1993ETG+ | 功能描述:电压模式 PWM 控制器 Step-Down w/Inductor RoHS:否 制造商:Texas Instruments 输出端数量:1 拓扑结构:Buck 输出电压:34 V 输出电流: 开关频率: 工作电源电压:4.5 V to 5.5 V 电源电流:600 uA 最大工作温度:+ 125 C 最小工作温度:- 40 C 封装 / 箱体:WSON-8 封装:Reel |
| MAX1993ETG+T | 功能描述:电压模式 PWM 控制器 Step-Down w/Inductor RoHS:否 制造商:Texas Instruments 输出端数量:1 拓扑结构:Buck 输出电压:34 V 输出电流: 开关频率: 工作电源电压:4.5 V to 5.5 V 电源电流:600 uA 最大工作温度:+ 125 C 最小工作温度:- 40 C 封装 / 箱体:WSON-8 封装:Reel |
| MAX1993ETG+TG40 | 制造商:Rochester Electronics LLC 功能描述: 制造商:Maxim Integrated Products 功能描述: |
| MAX1993ETG-T | 功能描述:电压模式 PWM 控制器 RoHS:否 制造商:Texas Instruments 输出端数量:1 拓扑结构:Buck 输出电压:34 V 输出电流: 开关频率: 工作电源电压:4.5 V to 5.5 V 电源电流:600 uA 最大工作温度:+ 125 C 最小工作温度:- 40 C 封装 / 箱体:WSON-8 封装:Reel |
| MAX1993EVKIT | 制造商:Maxim Integrated Products 功能描述:EVALUATION KIT FOR THE MAX1992 MAX1993 - Bulk |
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