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| 型号： | MAX5951ETJ+T |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 16/25页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM VM 32-TQFN |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 2,500 |
| PWM 型： | 电压模式 |
| 输出数： | 1 |
| 频率 - 最大： | 1MHz |
| 占空比： | 88% |
| 电源电压： | 4.5 V ~ 16 V |
| 降压： | 是 |
| 升压： | 无 |
| 回扫： | 无 |
| 反相： | 无 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 无 |
| 工作温度： | -40°C ~ 85°C |
| 封装/外壳： | 32-WFQFN 裸露焊盘 |
| 包装： | 带卷 (TR) |
12V/5V Input Buck PWM Controller
? V ESR
C OUT = STEP RESPONSE
The allowable deviation of the output voltage during
load transients also affects the choice of capacitance,
its ESR, and its equivalent series inductance (ESL). The
output capacitor supplies the load current during a
load step until the controller responds with a greater
duty cycle. The response time (t RESPONSE ) depends on
the closed-loop bandwidth of the converter (see the
Compensation Design Guidelines section). The resis-
tive drop across the output capacitor’s ESR, the drop
across the capacitor ’s ESL, and the capacitor dis-
charge cause a voltage droop during the load-step.
Use a combination of low-ESR tantalum/aluminum elec-
trolyte and ceramic capacitors for better load transient
and voltage ripple performance. Surface-mount capaci-
tors and capacitors in parallel help reduce the ESL.
Keep maximum output-voltage deviation below the tol-
erable limits of the electronics being powered. Use the
following equations to calculate the required ESR, ESL,
and capacitance value during a load step:
ESR =
I STEP
I × t
? V Q
The 20μA current source, ILIM reference current, has a
temperature coefficient of 3333ppm/°C. This allows the
valley current-limit threshold:
R ILIM × 20 μ A (T)
10
to track and compensate for the increase in the syn-
chronous MOSFET’s R DS(ON) with increasing tempera-
ture. MOSFETs typically have a temperature coefficient
range within 3000ppm/°C to 7000ppm/°C. Refer to the
MOSFET data sheet for a device-specific temperature
coefficient.
At a given temperature, the calculated V VALLEY must
be less than the minimum valley current-limit threshold
specified.
Figure 4 illustrates the effect of MAX5951 ILIM refer-
ence current temperature coefficient to compensate for
the variation of the MOSFET R DS(ON) over the operating
junction temperature range.
Power MOSFET Selection
When selecting the MOSFETs, consider the total gate
charge, R DS(ON) , power dissipation, the maximum
drain-to-source voltage, package thermal impedance,
and desired current limit. The product of the MOSFET
ESL =
? V ESL × t STEP
I STEP
gate charge and on-resistance is a figure of merit, with
a lower number signifying better performance. Choose
MOSFETs optimized for high-frequency switching
where I STEP is the load step, t STEP is the rise time of the
load step, and t RESPONSE is the response time of the
controller.
Setting the Current Limit
Connect a 25k ? to 175k ? resistor, R ILIM , from ILIM to
AGND to program the valley current-limit threshold
between 50mV and 350mV. ILIM sources 20μA out to
R ILIM . The resulting voltage divided by 10 is the valley
current-limit threshold.
applications. The average gate-drive current from the
MAX5951’s output is proportional to the frequency and
gate charge required to drive the MOSFET. The power
dissipated in the MAX5951 is proportional to the input
voltage and the average drive current (see the Power
Dissipation section).
VALLEY CURRENT-LIMIT THRESHOLD
AND R DS(ON) vs. TEMPERATURE
1.5
The MAX5951 uses a valley current-sense method for
current limiting. The voltage drop across the low-side
MOSFET due to its on-resistance is used to sense the
inductor current. The voltage drop across the low-side
MOSFET at the valley point and at I LOAD(MAX) is:
1.4
1.3
1.2
1.1
1.0
R DS(ON)
V ILIM
V VALLEY DS ( ON ) ( T ) × ? I LOAD ( MAX ) ?
= R
? I P ? P ?
?
?
?
?
2
0.9
0.8
0.7
R DS(ON) is the on-resistance of the low-side MOSFET,
0.6
which is temperature dependent, I LOAD(MAX) is the
maximum DC load current, and ? I P-P is the peak-to-
peak inductor current.
0.5
-40
-15
10 35
TEMPERATURE ( ° C)
60
85
Figure 4. Current-Limit Threshold and RDS(ON) vs.
Temperature
16
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| MAX5952AEVCMAXQU | 功能描述:热插拔功率分布 Evaluation Kit/Evaluation System for the MAX5952A RoHS:否 制造商:Texas Instruments 产品:Controllers & Switches 电流限制: 电源电压-最大:7 V 电源电压-最小:- 0.3 V 工作温度范围: 功率耗散: 安装风格:SMD/SMT 封装 / 箱体:MSOP-8 封装:Tube |
| MAX5952AEVKIT | 功能描述:电源管理IC开发工具 Evaluation Kit/Evaluation System for the MAX5952A 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 |
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