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参数资料
| 型号： | MAX8720EEI+ |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 27/31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
where N is the number of high-side MOSFETs used for
one regulator, and Q GATE is the gate charge specified
in the MOSFET’s data sheet. For example, assume the
IRF7821 n-channel MOSFET is used on the high side.
According to the manufacturer’s data sheet, a single
IRF7821 has a maximum gate charge of 14nC (V GS =
5V). Using the above equation, the required boost
capacitance is:
where V DIS and V CHG are the parasitic voltage drops in
the discharge and charge paths, respectively (see the
On-Time One-Shot (TON) section), t OFF(MIN) is from the
Electrical Characteristics table, and K is taken from
Table 3. The absolute minimum input voltage is calcu-
lated with h = 1.
If the calculated V IN(MIN) is greater than the required
minimum input voltage, then operating frequency must
C BST =
1 × 14nC
200 mV
= 0 . 07 μ F
be reduced or output capacitance added to obtain
an acceptable V SAG . If operation near dropout is
anticipated, calculate V SAG to be sure of adequate
transient response.
Select the closest standard value. This example
requires a 0.1μF ceramic capacitor.
Applications Information
Dropout Performance
The output-voltage adjust range for continuous-conduc-
tion operation is restricted by the nonadjustable 500ns
(max) minimum off-time one-shot (375ns max at
1000kHz). For best dropout performance, use the slower
(200kHz) on-time settings. When working with low input
voltages, the duty-factor limit must be calculated using
worst-case values for on- and off-times. Manufacturing
tolerances and internal propagation delays introduce an
error to the TON K-factor. This error is greater at higher
frequencies (Table 3). Also, keep in mind that transient-
response performance of buck regulators operated
close to dropout is poor, and bulk output capacitance
must often be added (see the V SAG equation in the
Design Procedure section).
The absolute point of dropout is when the inductor cur-
rent ramps down during the minimum off-time ( ? I DOWN )
as much as it ramps up during the on-time ( ? I UP ). The
ratio h = ? I UP / ? I DOWN is an indicator of the ability to
slew the inductor current higher in response to
increased load, and must always be greater than 1. As
h approaches 1, the absolute minimum dropout point,
the inductor current is less able to increase during
each switching cycle and V SAG greatly increases
unless additional output capacitance is used.
A reasonable minimum value for h is 1.5, but this may
be adjusted up or down to allow tradeoffs between
V SAG , output capacitance, and minimum operating
voltage. For a given value of h, the minimum operating
voltage can be calculated as:
Dropout Design Example:
V OUT = 1.6V
f SW = 550kHz
K = 1.8μs, worst-case K = 1.58μs
t OFF(MIN) = 500ns
V DIS = V CHG = 100mV
h = 1.5
V IN(MIN) = (1.6V + 0.1V) / (1 - 0.5μs x 1.5 / 1.58μs)
+ 0.1V - 0.1V = 3.2V
Calculating again with h = 1 gives the absolute limit
of dropout:
V IN(MIN) = (1.6V + 0.1V) / (1 - 0.5μs x 1.0 / 1.58μs)
+ 0.1V - 0.1V = 2.5V
Therefore, V IN must be greater than 2.5V, even with
very large output capacitance, and a practical input
voltage with reasonable output capacitance is 3.2V.
One-Stage (Battery Input) vs. Two-Stage
(5V Input) Applications
The MAX8720 can be used with a direct battery con-
nection (one stage) or can obtain power from a regulat-
ed 5V supply (two stage). Each approach has
advantages, and careful consideration should go into
the selection of the final design.
The one-stage approach offers smaller total inductor
size and fewer capacitors overall due to the reduced
demands on the 5V supply. The transient response of
the single stage is better due to the ability to ramp up
the inductor current faster. The total efficiency of a sin-
gle stage is better than the two-stage approach.
The two-stage approach allows flexible placement due
V IN(MIN) = ?
t × h ?
? 1 ? OFF(MIN) ?
?
?
? K ?
V OUT + V DIS
+ V CHG ? V DIS
to smaller circuit size and reduced local power dissipa-
tion. The power supply can be placed closer to the
CPU for better regulation and lower I 2 R losses from PC
board traces. Although the two-stage design has worse
transient response than the single stage, this can be
offset by the use of a voltage-positioned converter.
______________________________________________________________________________________
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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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