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| 型号： | MAX8792ETD+T |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 25/28页 |
| 文件大小： | 0K |
| 描述： | IC PWM CTRLR STEP-DWN 14TDFN |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 1 |
| 应用： | PWM 控制器 |
| 输入电压： | 2 V ~ 26 V |
| 电源电压： | 4.5 V ~ 5.5 V |
| 电流 - 电源： | 700µA |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 14-WFDFN 裸露焊盘 |
| 供应商设备封装： | 14-TDFN-EP（3x3） |
| 包装： | 标准包装 |
| 其它名称： | MAX8792ETD+TDKR |
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Single Quick-PWM Step-Down
Controller with Dynamic REFIN
Switching ) = V f
?+
? I GATE ?
rough estimate and is no substitute for breadboard
evaluation, preferably including verification using a
thermocouple mounted on N H :
? Q G ( SW ) ?
PD ( N H IN ( MAX ) I LOAD SW ?
C OSS V IN 2 f SW
2
where C OSS is the N H MOSFET’s output capacitance,
Q G(SW) is the charge needed to turn on the N H MOS-
Boost Capacitors
The boost capacitors (C BST ) must be selected large
enough to handle the gate charging requirements of
the high-side MOSFETs. Typically, 0.1 μF 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 applica-
tions, select the boost capacitors to avoid discharging
the capacitor more than 200mV while charging the
high-side MOSFETs’ gates:
FET, and I GATE is the peak gate-drive source/sink cur-
rent (2.2A typ).
Switching losses in the high-side MOSFET can become
C BST =
N × Q GATE
200 mV
? ? ( I LOAD ) R DS ( ON )
? V IN ( MAX ) ? ? ?
PD ( N L Re sistive ) = ? 1 ? ?
C BST =
= 0 . 24 μ F
I LOAD VALLEY ( MAX ) +
= I
= I VALLEY ( MAX ) + ?
?
?
?
an insidious heat problem when maximum AC adapter
voltages are applied, due to the squared term in the C
x V IN 2 x f SW switching-loss equation. If the high-side
MOSFET chosen for adequate R DS(ON) at low battery
voltages becomes extraordinarily hot when biased from
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 input voltage:
? ? V OUT ? ? 2
? ?
The worst case for MOSFET power dissipation occurs
under heavy overloads that are greater than
I LOAD(MAX) , but are not quite high enough to exceed
the current limit and cause the fault latch to trip. To pro-
tect against this possibility, you can “overdesign” the
circuit to tolerate:
Δ I L
2
? I LOAD ( MAX ) LIR ?
2
where I VALLEY(MAX) is the maximum valley current
allowed by the current-limit circuit, including threshold
tolerance and on-resistance variation. The MOSFETs
must have a good size heatsink to handle the overload
power dissipation.
Choose a Schottky diode (D L ) with a forward voltage
low enough to prevent the low-side MOSFET body
diode from turning on during the dead time. Select a
diode that can handle the load current during the dead
times. This diode is optional and can be removed if effi-
ciency is not critical.
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 (2)
IRF7811W n-channel MOSFETs are used on the high
side. According to the manufacturer’s data sheet, a sin-
gle IRF7811W has a maximum gate charge of 24nC
(V GS = 5V). Using the above equation, the required
boost capacitance would be:
2 × 24nC
200 mV
Selecting the closest standard value, this example
requires a 0.22μF ceramic capacitor.
Minimum Input-Voltage Requirements
and Dropout Performance
The output voltage-adjustable range for continuous-
conduction operation is restricted by the nonadjustable
minimum off-time one-shot. For best dropout perfor-
mance, 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 propa-
gation delays introduce an error to the on-times. This
error is greater at higher frequencies. Also, keep in
mind that transient response performance of buck reg-
ulators operated too close to dropout is poor, and bulk
output capacitance must often be added (see the V SAG
equation in the Quick-PWM Design Procedure section).
The absolute point of dropout is when the inductor cur-
rent ramps down during the minimum off-time ( Δ I DOWN )
as much as it ramps up during the on-time ( Δ I UP ). The
ratio h = Δ I UP / Δ 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 cannot increase as much during
each switching cycle and V SAG greatly increases
unless additional output capacitance is used.
______________________________________________________________________________________
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| MAX8792EVKIT+ | 功能描述:电源管理IC开发工具 MAX8792 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 |
| MAX8794ETB/V+T | 功能描述:低压差稳压器 - LDO Low-Voltage DDR Linear Regulator RoHS:否 制造商:Texas Instruments 最大输入电压:36 V 输出电压:1.4 V to 20.5 V 回动电压（最大值）:307 mV 输出电流:1 A 负载调节:0.3 % 输出端数量: 输出类型:Fixed 最大工作温度:+ 125 C 安装风格:SMD/SMT 封装 / 箱体:VQFN-20 |
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| MAX8794ETB+T | 功能描述:低压差稳压器 - LDO Low-Voltage DDR Linear Regulator RoHS:否 制造商:Texas Instruments 最大输入电压:36 V 输出电压:1.4 V to 20.5 V 回动电压（最大值）:307 mV 输出电流:1 A 负载调节:0.3 % 输出端数量: 输出类型:Fixed 最大工作温度:+ 125 C 安装风格:SMD/SMT 封装 / 箱体:VQFN-20 |
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