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| 型号： | MAX1710 |
| 厂商： | Maxim Integrated Products, Inc. |
| 英文描述： | High-Speed, Digitally Adjusted Step-Down Controllers for Notebook CPUs |
| 中文描述： | 高速、数字可调、降压型控制器，用于笔记本电脑 |
| 文件页数： | 14/28页 |
| 文件大小： | 299K |
| 代理商： | MAX1710 |
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M
High-S peed, Digitally Adjusted
S tep-Down Controllers for Notebook CPUs
14
______________________________________________________________________________________
Figure 4. ‘‘Valley’’ Current-Limit Threshold Point
I
I
LIMIT
I
LOAD
0
TIME
LX-PGND I
THRESHOLD = 100mV (NOMINAL, DEFAULT)
VOLTAGE DROP ACROSS Q2
-I
PEAK
about 1/4 full load. The crossover point occurs at an
even lower value if a swinging (soft-saturation) inductor
is used.
The switching waveforms may appear noisy and asyn-
chronous when light loading causes pulse-skipping
operation, but this is a normal operating condition that
results in high light-load efficiency. Trade-offs in PFM
noise vs. light-load efficiency can be made by varying
the inductor value. Generally, low inductor values pro-
duce a broader efficiency vs. load curve, while higher
values result in higher full-load efficiency (assuming that
the coil resistance remains fixed) and less output voltage
ripple. Penalties for using higher inductor values include
larger physical size and degraded load-transient
response (especially at low input voltage levels).
Forced-PWM Mode (
SKIP
= High)
The low-noise, forced-PWM mode (
SKIP
driven high) dis-
ables the zero-crossing comparator, which controls the
low-side switch on-time. This causes the low-side gate-
drive waveform to become the complement of the high-
side gate-drive waveform. This in turn causes the
inductor current to reverse at light loads, as the PWM
loop strives to maintain a duty ratio of V
OUT
/V
IN
. The
benefit of forced-PWM mode is to keep the switching fre-
quency fairly constant, but it comes at a cost: the no-
load battery current can be as high as 40mA or more.
Forced-PWM mode is most useful for reducing audio-fre-
quency noise, improving load-transient response, pro-
viding sink-current capability for dynamic output voltage
adjustment, and improving the cross-regulation of multi-
ple-output applications that use a flyback transformer or
coupled inductor.
Current-Limit Circuit (ILIM)
The current-limit circuit employs a unique “valley” cur-
rent-sensing algorithm that uses the on-state resistance
of the low-side MOSFET as a current-sensing element. If
the current-sense signal is above the current-limit
threshold, the PWM is not allowed to initiate a new cycle
(Figure 4). The actual peak current is greater than the
current-limit threshold by an amount equal to the induc-
tor ripple current. Therefore the exact current-limit char-
acteristic and maximum load capability are a function of
the MOSFET on-resistance, inductor value, and battery
voltage. The reward for this uncertainty is robust, loss-
less overcurrent sensing. When combined with the UVP
protection circuit, this current-limit method is effective in
almost every circumstance.
There is also a negative current limit that prevents exces-
sive reverse inductor currents when V
OUT
is sinking cur-
rent. The negative current-limit threshold is set to
approximately 120% of the positive current limit, and
therefore tracks the positive current limit when ILIM is
adjusted.
The current-limit threshold can be adjusted with an exter-
nal resistor (R
LIM
) at ILIM. A precision 5μA pull-up cur-
rent source at ILIM sets a voltage drop on this resistor,
adjusting the current-limit threshold from 50mV to
200mV. In the adjustable mode, the current-limit thresh-
old voltage is precisely 1/10th the voltage seen at ILIM.
Therefore, choose R
LIM
equal to 2k
/mV of the current-
limit threshold. The threshold defaults to 100mV when
ILIM is tied to V
CC
. The logic threshold for switchover to
the 100mV default value is approximately V
CC
- 1V.
The adjustable current limit can accommodate
MOSFETs with atypical on-resistance characteristics
(see Design Procedure).
A capacitor in parallel with R
LIM
can provide a variable
soft-start function.
Carefully observe the PC board layout guidelines to
ensure that noise and DC errors don’t corrupt the cur-
rent-sense signals seen by LX and PGND. The IC must
be mounted close to the low-side MOSFET with short,
Figure 3. Pulse-Skipping/Discontinuous Crossover Point
I
I
LOAD
= I
PEAK
/2
ON-TIME
0
TIME
-I
PEAK
L
V
BATT
-V
OUT
i
t
=
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相关代理商/技术参数 |
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| MAX17100ETM+C8W | 制造商:Maxim Integrated Products 功能描述:1.2MHZ STEP-UP DC-DC CONVERTER - Rail/Tube |
| MAX17100ETM+T | 功能描述:其他电源管理 Internal-Switch Boost Regulator RoHS:否 制造商:Texas Instruments 输出电压范围: 输出电流:4 mA 输入电压范围:3 V to 3.6 V 输入电流: 功率耗散: 工作温度范围:- 40 C to + 110 C 安装风格:SMD/SMT 封装 / 箱体:VQFN-48 封装:Reel |
| MAX17100EVKIT+ | 功能描述:电源管理IC开发工具 MAX17100 Eval Kit RoHS:否 制造商:Maxim Integrated 产品:Evaluation Kits 类型:Battery Management 工具用于评估:MAX17710GB 输入电压: 输出电压:1.8 V |
| MAX17101+SMP | 功能描述:DC/DC 开关控制器 RoHS:否 制造商:Texas Instruments 输入电压:6 V to 100 V 开关频率: 输出电压:1.215 V to 80 V 输出电流:3.5 A 输出端数量:1 最大工作温度:+ 125 C 安装风格: 封装 / 箱体:CPAK |
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