- 您现在的位置：买卖IC网 > PDF目录1849 > MAX8792ETD+T (Maxim Integrated Products)IC PWM CTRLR STEP-DWN 14TDFN PDF资料下载
参数资料
| 型号： | MAX8792ETD+T |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 20/28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 |
第1页第2页第3页第4页第5页第6页第7页第8页第9页第10页第11页第12页第13页第14页第15页第16页第17页第18页第19页当前第20页第21页第22页第23页第24页第25页第26页第27页第28页
Single Quick-PWM Step-Down
Controller with Dynamic REFIN
capacitor selection, inductor saturation rating, and
the design of the current-limit circuit. The continu-
ous load current (I LOAD ) determines the thermal
which can be calculated from the on-time and minimum
off-time. The worst-case output sag voltage can be
determined by:
L ( Δ I LOAD(MAX) ) ? ? OUT SW ? + t OFF ( MIN ) ?
? ?
?
? ? ( V IN ? V OUT ) T SW ?
? ? ?
? ?
2 C OUT V OUT ? ? ? ? t OFF ( MIN ) ?
?
stresses and thus drives the selection of input
capacitors, MOSFETs, and other critical heat-con-
tributing components. Most notebook loads gener-
ally exhibit I LOAD = I LOAD(MAX) x 80%.
Switching frequency: This choice determines the
basic trade-off between size and efficiency. The
V SAG =
2 ? ? V T ? ?
V IN ?
V IN ?
?
optimal frequency is largely a function of maximum
input voltage due to MOSFET switching losses that
are proportional to frequency and V IN 2 . The opti-
mum frequency is also a moving target, due to
rapid improvements in MOSFET technology that are
where t OFF(MIN) is the minimum off-time (see the Electrical
Characteristics table).
The amount of overshoot due to stored inductor energy
when the load is removed can be calculated as:
?
making higher frequencies more practical.
Inductor operating point: This choice provides
trade-offs between size vs. efficiency and transient
V SOAR ≈
( Δ I LOAD(MAX ) ) 2 L
2 C OUT V OUT
response vs. output noise. Low inductor values pro-
vide better transient response and smaller physical
size, but also result in lower efficiency and higher
output noise due to increased ripple current. The
minimum practical inductor value is one that causes
the circuit to operate at the edge of critical conduc-
tion (where the inductor current just touches zero
Setting the Valley Current Limit
The minimum current-limit threshold must be high
enough to support the maximum load current when the
current limit is at the minimum tolerance value. The val-
ley of the inductor current occurs at I LOAD(MAX) minus
half the inductor ripple current ( Δ IL); therefore:
with every cycle at maximum load). Inductor values
lower than this grant no further size-reduction bene-
fit. The optimum operating point is usually found
I LIMIT ( LOW ) > I LOAD ( MAX ) ?
Δ I L
2
f SW LOAD ( MAX ) LIR ? ? ? V IN ?
L = ? ? ?
?
I PEAK = I LOAD ( MAX ) +
between 20% and 50% ripple current.
Inductor Selection
The switching frequency and operating point (% ripple
current or LIR) determine the inductor value as follows:
? V IN ? V OUT ? ? V OUT ?
I
Find a low-loss inductor having the lowest possible DC
resistance that fits in the allotted dimensions. Ferrite
cores are often the best choice, although powdered
iron is inexpensive and can work well at 200kHz. The
core must be large enough not to saturate at the peak
inductor current (I PEAK ):
Δ I L
2
Transient Response
The inductor ripple current impacts transient-response
performance, especially at low V IN - V OUT differentials.
Low inductor values allow the inductor current to slew
faster, replenishing charge removed from the output fil-
ter capacitors by a sudden load step. The amount of
output sag is also a function of the maximum duty factor,
where I LIMIT(LOW) equals the minimum current-limit
threshold voltage divided by the low-side MOSFETs on-
resistance (R DS(ON) ).
The valley current-limit threshold is precisely 1/20 the
voltage seen at ILIM. Connect a resistive divider from
REF to ILIM to analog ground (GND) in order to set a
fixed valley current-limit threshold. The external 400mV to
2V adjustment range corresponds to a 20mV to 100mV
valley current-limit threshold. When adjusting the current-
limit threshold, use 1% tolerance resistors and a divider
current of approximately 5μA to 10μA to prevent signifi-
cant inaccuracy in the valley current-limit tolerance.
The MAX8792 uses the low-side MOSFET’s on-resis-
tance as the current-sense element (R SENSE =
R DS(ON) ). Therefore, special attention must be made to
the tolerance and thermal variation of the on-resistance.
Use the worst-case maximum value for R DS(ON) from
the MOSFET data sheet, and add some margin for the
rise in R DS(ON) with temperature. A good general rule is
to allow 0.5% additional resistance for each °C of tem-
perature rise, which must be included in the design
margin unless the design includes an NTC thermistor in
the ILIM resistive voltage-divider to thermally compen-
sate the current-limit threshold.
20
______________________________________________________________________________________
相关PDF资料 |
PDF描述 |
|---|---|
| MAX8794ETB+T | IC DDR LINEAR REG 10-TDFN |
| MAX8795AETJ+C7P | IC TFT-LCD DC/DC CONV 32-TQFN |
| MAX8798ETX+T | IC INTERNAL-SW BOOST REG 36-TQFN |
| MAX8804VETA+T | IC USB/AC ADP CHARGER 8TDFN-EP |
| MAX8804YETA+T | IC USB/AC ADP CHARGER 8-TDFN |
相关代理商/技术参数 |
参数描述 |
|---|---|
| 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 |
| MAX8794ETB+ | 制造商:Maxim Integrated Products 功能描述: 制造商:Maxim Integrated Products 功能描述:LOW-VOLTAGE DDR LINEAR REGULATOR - Rail/Tube |
| 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 |
| MAX8795AETJ+ | 功能描述:直流/直流开关转换器 TFT-LCD DC/DC Converter RoHS:否 制造商:STMicroelectronics 最大输入电压:4.5 V 开关频率:1.5 MHz 输出电压:4.6 V 输出电流:250 mA 输出端数量:2 最大工作温度:+ 85 C 安装风格:SMD/SMT |
发布紧急采购，3分钟左右您将得到回复。