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参数资料
| 型号： | MAX17101ETJ+T |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 24/31页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR DIV PWM CM 32TQFNEP |
| 标准包装： | 2,500 |
| PWM 型： | 电流模式 |
| 输出数： | 3 |
| 频率 - 最大： | 500kHz |
| 电源电压： | 6 V ~ 24 V |
| 降压： | 是 |
| 升压： | 无 |
| 回扫： | 无 |
| 反相： | 无 |
| 倍增器： | 无 |
| 除法器： | 是 |
| Cuk： | 无 |
| 隔离： | 无 |
| 工作温度： | 0°C ~ 85°C |
| 封装/外壳： | 32-WFQFN 裸露焊盘 |
| 包装： | 带卷 (TR) |
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Dual Quick-PWM, Step-Down Controller
with Low-Power LDO, RTC Regulator
L = RIPPLE IN OUT
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 primary
design trade-off lies in choosing a good switching fre-
quency and inductor operating point, and the following
four factors dictate the rest of the design:
Inductor Selection
The switching frequency and inductor operating point
determine the inductor value as follows:
V (V ? V )
V IN f SW I LOAD ( MAX ) LIR
For example: I LOAD(MAX) = 4A, V IN = 12V, V OUT2 =
?
Input Voltage Range: The maximum value
2.5V, f SW = 355kHz, 30% ripple current or LIR = 0.3:
(V IN(MAX) ) must accommodate the worst-case, high
AC-adapter voltage. The minimum value (V IN(MIN) )
must account for the lowest battery voltage after
L =
2 . 5 V × ( 12 V ? 2 . 5 V )
12 V × 355 kHz × 4 A × 0 . 3
= 4 . 65 μH
drops due to connectors, fuses, and battery-selector
switches. If there is a choice at all, lower input volt-
ages result in better efficiency.
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
I PEAK = I LOAD ( MAX ) ? 1 +
?
?
?
?
Maximum Load Current: There are two values to
consider. The peak load current (I LOAD(MAX) )
determines the instantaneous component stresses
and filtering requirements and thus drives output
capacitor selection, inductor saturation rating, and
the design of the current-limit circuit. The conti-
nuous load current (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 opti-
mal frequency is largely a function of maximum input
voltage due to MOSFET switching losses that are
proportional to frequency and V IN 2 . The optimum fre-
quency is also a moving target due to rapid improve-
ments in MOSFET technology that are making higher
frequencies more practical.
Inductor Operating Point: This choice provides
trade-offs between size vs. efficiency and transient
response vs. output ripple. Low inductor values
provide better transient response and smaller phy-
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 ):
? LIR ?
? 2 ?
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
inductance decreases linearly with increasing current),
evaluate the LIR with properly scaled inductance values.
Transient Response
The inductor ripple current also impacts 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 amount of output sag is also a function of the maxi-
mum duty factor, which can be calculated from the on-
time and minimum off-time:
) 2 ? ? ? ? V OUTIN K ? ? ? + t OFF ( MIN ) ?
(
L Δ I LOAD ( MAX )
?
?
? ? ( V IN ? V OUT ) K ?
2C OUT V OUT ? ? ? ? t OFF ( M IN)
? ? ?
sical size, but also result in lower efficiency and
higher output ripple due to increased ripple cur-
rents. The minimum practical inductor value is one
that causes the circuit to operate at the edge of cri-
tical conduction (where the inductor current just
touches zero with every cycle at maximum load).
Inductor values lower than this grant no further size-
V SAG =
? ?
V
V IN
( Δ I LOAD ( MAX ) ) 2 L
reduction benefit. 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.
where t OFF(MIN) is the minimum off-time (see the
Electrical Characteristics) and K is from Table 3.
The amount of overshoot during a full-load to no-load tran-
sient due to stored inductor energy can be calculated as:
V SOAR ≈
2 C OUT V OUT
24
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