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参数资料
| 型号： | MAX8720EEI+T |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 26/31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： | 2,500 |
| 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： | 带卷 (TR) |
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Dynamically Adjustable 6-Bit VID
Step-Down Controller
PD ( N L RESISTIVE ) = ? 1 ? ? ? ? ( I LOAD DS ( ON )
) 2 R
) 2 × R
PD ( N H RESISTIVE ) = ? OUT ? ( I LOAD DS ( ON )
I LOAD LIMIT ? ?
? I LOAD ( MAX ) LIR ?
?
PD ( N H SWITCHING ) =
C BST =
significantly higher, consider increasing the size of N H .
Conversely, if the losses at V IN(MAX) are significantly
higher, consider reducing the size of N H . If V IN does
not vary over a wide range, maximum efficiency is
achieved by selecting a high-side MOSFET (N H ) that
has conduction losses equal to the switching losses.
Choose a low-side MOSFET (N L ) that has the lowest
possible on-resistance (R DS(ON) ), comes in a moder-
ate-sized package (i.e., SO-8, DPAK, or D 2 PAK), and is
reasonably priced. Ensure that the MAX8720 DL gate
driver can supply sufficient current to support the gate
charge and the current injected into the parasitic drain-
to-gate capacitor caused by the high-side MOSFET
turning on; otherwise, cross-conduction problems may
occur. Switching losses are not an issue for the low-
side MOSFET since it is a zero-voltage switched device
when used in the step-down topology.
Power MOSFET Dissipation
Worst-case conduction losses occur at the duty-factor
extremes. For the high-side MOSFET (N H ), the worst-
case power dissipation due to resistance occurs at the
minimum input voltage:
? V ?
? V IN ?
Generally, use a small high-side MOSFET to reduce
switching losses at high input voltages. However, the
R DS(ON) required to stay within package power-dissi-
pation limits often limits how small the MOSFET can be.
The optimum occurs when the switching losses equal
the conduction (R DS(ON) ) losses. High-side switching
losses do not become an issue until the input is greater
than approximately 15V.
Calculating the power dissipation in high-side
MOSFETs (N H ) due to switching losses is difficult, since
it must allow for difficult-to-quantify factors that influ-
ence the turn-on and turn-off times. These factors
include the internal gate resistance, gate charge,
threshold voltage, source inductance, and PC board
layout characteristics. The following switching loss cal-
culation provides only a very rough estimate and is no
substitute for breadboard evaluation, preferably includ-
ing verification using a thermocouple mounted on N H :
( V IN ( MAX ) ) 2 C RSS f SW I LOAD
I GATE
where C RSS is the reverse transfer capacitance of N H ,
and I GATE is the peak gate-drive source/sink current
(2A typ).
Switching losses in the high-side MOSFET can become
a heat problem when maximum AC-adapter voltages
are applied, due to the squared term in the switching-
loss equation (C x V IN 2 x f SW ). If the high-side MOSFET
chosen for adequate R DS(ON) at low battery voltages
becomes extraordinarily hot when subjected to
V IN(MAX) , consider choosing another MOSFET with
lower parasitic capacitance.
For the low-side MOSFET (N L ), the worst-case power
dissipation always occurs at maximum battery voltage:
? ? V ? ?
OUT
? ?
? ? V IN ( MAX ) ? ?
The absolute worst case for MOSFET power dissipation
occurs under heavy overload conditions that are
greater than I LOAD(MAX) but are not high enough to
exceed the current limit and cause the fault latch to trip.
To protect against this possibility, “overdesign” the cir-
cuit to tolerate:
= I
? 2 ?
where I LIMIT is the peak current allowed by the current-
limit circuit, including threshold tolerance and sense-
resistance variation. The MOSFETs must have a
relatively large heatsink to handle the overload power
dissipation.
Choose a Schottky diode (D L ) with a forward-voltage
drop low enough to prevent the low-side MOSFET’s
body diode from turning on during the dead time. As a
general rule, select a diode with a DC current rating
equal to 1/3rd of the load current. This diode is optional
and can be removed if efficiency is not critical.
Boost Capacitors
The boost capacitors (C BST ) must be selected large
enough to handle the gate-charging requirements of
the high-side MOSFETs. Typically, 0.1μF ceramic
capacitors work well for low-power applications driving
medium-sized MOSFETs. However, high-current appli-
cations driving large, high-side MOSFETs require boost
capacitors larger than 0.1μF. For these applications,
select the boost capacitors to avoid discharging the
capacitor more than 200mV while charging the high-
side MOSFETs’ gates:
N × Q GATE
200 mV
26
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相关代理商/技术参数 |
参数描述 |
|---|---|
| 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 |
| MAX8720ETX+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 |
| MAX8720ETX-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 |
| MAX8720EVKIT | 功能描述:DC/DC 开关控制器 Evaluation Kit for the MAX8720 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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