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| 型号： | MAX1545ETL+T |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 32/43页 |
| 文件大小： | 0K |
| 描述： | IC QUICK-PWM DUAL-PHASE 40-TQFN |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 2,500 |
| 系列： | Quick-PWM™ |
| 应用： | 控制器，Intel Pentium? IV |
| 输入电压： | 2 V ~ 28 V |
| 输出数： | 1 |
| 输出电压： | 0.6 V ~ 1.85 V |
| 工作温度： | -40°C ~ 100°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 40-WFQFN 裸露焊盘 |
| 供应商设备封装： | 40-TQFN-EP（6x6） |
| 包装： | 带卷 (TR) |
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Dual-Phase, Quick-PWM Controllers for
Programmable CPU Core Power Supplies
V SOAR ≈
2 η TOTAL C OUT OUT
L = η TOTAL ?
? f SW I LOAD ( MAX ) LIR ? ? V IN ?
I LIMIT ( LOW ) > ? LOAD ( MAX ) ? ? 1 ?
η TOTAL ? ?
2 ?
response vs. output noise. Low-inductor values pro-
vide better transient response and smaller physical
size, but also result in lower efficiency and higher out-
put noise due to increased ripple current. The mini-
mum practical inductor value is one that causes the
circuit to 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 operating point is usually found between
20% and 50% ripple current.
Inductor Selection
The switching frequency and operating point (% ripple
current or LIR) determine the inductor value as follows:
? V IN ? V OUT ? ? V OUT ?
? ? ?
where η TOTAL is the total number of phases.
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 ):
can be calculated as:
( Δ I LOAD ( MAX ) ) 2 L
V
where η TOTAL is the total number of active phases.
Setting the Current Limit
The minimum current-limit threshold must be high
enough to support the maximum load current when the
current limit is at the minimum tolerance value. The valley
of the inductor current occurs at I LOAD(MAX) minus half
the ripple current; therefore:
? I ? ? LIR ?
?
?
where η TOTAL is the total number of active phases, and
I LIMIT(LOW) equals the minimum current-limit threshold
voltage divided by the current-sense resistor (R SENSE ).
For the 30mV default setting, the minimum current-limit
threshold is 28mV.
Connect ILIM to V CC for the default current-limit thresh-
old (see the Electrical Characteristics ). In adjustable
mode, the current-limit threshold is precisely 1/20 the
voltage seen at ILIM. For an adjustable threshold, con-
I PEAK = ? LOAD ( MAX ) ? ? 1 +
? η TOTAL ?
?
? I ? ?
?
LIR ?
2 ?
nect a resistive divider from REF to GND with ILIM con-
nected to the center tap. When adjusting the current
limit, use 1% tolerance resistors with approximately 10μA
of divider current to prevent a significant increase of
Transient Response
The inductor ripple current impacts transient-response
performance, especially at low V IN - V OUT differentials.
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 maximum duty factor, which
can be calculated from the on-time and minimum off-
time. For a dual-phase controller, the worst-case output
sag voltage can be determined by:
errors in the current-limit tolerance.
Output Capacitor Selection
The output filter capacitor must have low enough effec-
tive series resistance (ESR) to meet output ripple and
load-transient requirements, yet have high enough ESR
to satisfy stability requirements.
In CPU V CORE converters and other applications where
the output is subject to large load transients, the output
capacitor’s size typically depends on how much ESR is
needed to prevent the output from dipping too low
L ( Δ I LOAD ( MAX ) ) 2 ? ? OUT ? + t OFF ( MIN ) ?
? ?
? ?
? ? 2 t OFF ( MIN )
? ?
2 C OUT V OUT ? ?
R ESR ≤
V SAG =
? ? V K ? ?
? V IN ?
? ? ( V IN ? 2 V OUT ) K ?
V IN ?
?
under a load transient. Ignoring the sag due to finite
capacitance:
V STEP
Δ I LOAD ( MAX )
? + t OFF ( MIN ) ?
Δ I LOAD ( MAX ) ? ? V OUT K ? ?
?
V IN ?
?
?
+ ? ?
2 C OUT
where t OFF(MIN) is the minimum off-time (see the
Electrical Characteristics ) and K is from Table 6.
The amount of overshoot due to stored inductor energy
In non-CPU applications, the output capacitor’s size
often depends on how much ESR is needed to maintain
an acceptable level of output ripple voltage. The output
ripple voltage of a step-down controller equals the total
inductor ripple current multiplied by the output capaci-
tor’s ESR. When operating multiphase systems out-of-
32
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