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| 型号： | MAX8720EEI+ |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 15/31页 |
| 文件大小： | 0K |
| 描述： | IC CNTRL VID STP DWN 28-QSOP |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 50 |
| 应用： | 控制器，CPU GPU |
| 输入电压： | 2 V ~ 28 V |
| 输出数： | 1 |
| 输出电压： | 0.28 V ~ 1.85 V |
| 工作温度： | 0°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 28-QSOP |
| 供应商设备封装： | 28-QSOP |
| 包装： | 管件 |
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Dynamically Adjustable 6-Bit VID
Step-Down Controller
dynamic output-voltage transitions when the inductor
current reverses at light or negative load currents. With
reversed inductor current, the inductor’s EMF causes LX
to go high earlier than normal, extending the on-time by
a period equal to the DH-rising dead time.
For loads above the critical conduction point, where the
dead-time effect is no longer a factor, the actual switch-
ing frequency is:
This can work very well if the MAX8720 circuit is placed
very close to the CPU. All three integrators can be dis-
abled by connecting FBS to V CC . When the integrators
are disabled, CC can be left unconnected, which elimi-
nates a component but leaves GNDS connected to any
convenient ground. When the inductor is in continuous
conduction, the output voltage has a DC regulation high-
er than the trip level by 50% of the ripple. In discontinu-
ous conduction ( SKIP = GND, light loaded), the output
f SW =
V OUT + V DIS
t ON ( V IN + V DIS ? V CHG )
voltage has a DC regulation higher than the trip level by
approximately 1.5% due to slope compensation.
There is often a connector, or at least many milliohms of
where V DIS is the sum of the parasitic voltage drops in
the inductor discharge path, including synchronous
rectifier, inductor, and PC board resistances; V CHG is
the sum of the parasitic voltage drops in the inductor
charge path, including high-side switch, inductor, and
PC board resistances; and t ON is the on-time calculat-
ed by the MAX8720.
Integrator Amplifiers and
Output-Voltage Offsets
Three integrator amplifiers provide a fine adjustment to
the output regulation point. One amplifier integrates the
difference between GNDS and AGND, and a second
integrates the difference between FBS and FB. The
third amplifier integrates the difference between REF
and the DAC output. These three transconductance
amplifiers’ outputs are directly summed inside the chip,
so the integration time constant can be set easily with
one capacitor. The G m of each amplifier is 160μS (typ).
The integrator block has the ability to lower the output
voltage by 2% and raise it by 6%. For each amplifier,
the differential input voltage range is at least ±70mV
total, including DC offset and AC ripple. The integrator
corrects for approximately 90% of the total error, due to
finite gain.
The FBS amplifier corrects for DC voltage drops in PC
board traces and connectors in the output bus path
between the DC-DC converter and the load. The GNDS
amplifier performs a similar DC correction task for the
output ground bus. The third integrator amplifier cor-
rects the small offset of the error amplifier and provides
an averaging function that forces V OUT to be regulated
at the average value of the output ripple waveform.
Integrators have both beneficial and detrimental charac-
teristics. Although they correct for drops due to DC bus
resistance and tighten the DC output-voltage tolerance
limits by averaging the peak-to-peak output ripple, they
can interfere with achieving the fastest possible load-
transient response. The fastest transient response is
achieved when all three integrators are disabled.
PC board trace resistance, between the DC-DC con-
verter and the CPU. In these cases, the best strategy is
to place most of the bulk bypass capacitors close to
the CPU, with just one capacitor on the other side of the
connector near the MAX8720 to control ripple if the
CPU card is unplugged. In this situation, the remote-
sense lines (GNDS and FBS) and integrators provide a
real benefit.
Forced-PWM Mode ( SKIP = High)
The low-noise forced-PWM mode ( SKIP = high) dis-
ables the zero-crossing comparator, allowing the
inductor current to reverse at light loads. This causes
the low-side gate-drive waveform to become the com-
plement of the high-side gate-drive waveform. The ben-
efit of forced-PWM mode is to keep the switching
frequency fairly constant, but it comes at a cost: the no-
load battery current can be 10mA to 40mA, depending
on the external MOSFETs and switching frequency.
Forced-PWM mode is required during downward out-
put-voltage transitions. The MAX8720 uses PWM mode
during all transitions, but only while the slew-rate con-
troller is active. Due to voltage positioning, when a tran-
sition uses high negative inductor current, the output
voltage does not settle to its final intended value until
well after the slew-rate controller terminates. Because
of this it is possible, at very high negative slew currents,
for the output to end up high enough to cause PGOOD
to go low.
Thus, it is necessary to use forced-PWM mode during all
negative transitions. Most applications should use PWM
mode exclusively, although there is some benefit to
using skip mode while in the low-power suspend state.
Automatic Pulse-Skipping Switchover
( SKIP = GND)
In skip mode ( SKIP = GND), an inherent automatic
switchover to PFM takes place at light loads (Figure 3).
This switchover is affected by a comparator that trun-
cates the low-side switch on-time at the inductor cur-
rent ’s zero crossing. This mechanism causes the
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相关代理商/技术参数 |
参数描述 |
|---|---|
| MAX8720EEI+ | 功能描述:DC/DC 开关控制器 Dyn Adj 6-Bit VID Step-Down Controller 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 |
| MAX8720EEI+T | 功能描述:DC/DC 开关控制器 Dyn Adj 6-Bit VID Step-Down Controller 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 |
| MAX8720EEI-T | 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 |
| MAX8720ETX | 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 |
| MAX8720ETX+ | 功能描述:DC/DC 开关控制器 Dyn Adj 6-Bit VID Step-Down Controller 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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