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| 型号： | MAX5953BUTM+ |
| 厂商： | Maxim Integrated |
| 文件页数： | 18/27页 |
| 文件大小： | 371K |
| 描述： | IC INTERFACE 802.3AF 48TQFN |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 43 |
| 类型： | 以太网供电开关（PoE） |
| 应用： | 远程外设（工业控制，相机，数据访问） |
| 内部开关： | 是 |
| 电源电压： | 11 V ~ 76 V |
| 工作温度： | 0°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 48-WFQFN 裸露焊盘 |
| 供应商设备封装： | 48-TQFN-EP（7x7） |
| 包装： | 管件 |
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Soft-Start
Program the MAX5953A/MAX5953B/MAX5953C/
MAX5953D soft-start with an external capacitor (C
CSS
)
connected between CSS and GND. When the device
turns on, C
CSS
charges with a constant current of
33礎, ramping up to 7.3V. During this time, the feed-
back input (OPTO) is clamped to V
CSS
+ 0.6V. This ini-
tially holds the duty cycle lower than the value the
regulator imposes, thus preventing voltage overshoot at
the output. When the IC turns off, the soft-start capaci-
tor internally discharges to GND.
Oscillator
The oscillator is externally programmable through a
resistor connected from RTCT to REGOUT and a
capacitor connected from RTCT to GND. The PWM fre-
quency is one-half the frequency seen at RTCT with a
50% duty cycle. Use the following formula to calculate
the oscillator components:
where C
PCB
is the stray capacitance on the PC board
(14pF, typ), V
TH,RTCT
is the RTCT peak trip level, and
f
S
is the switching frequency.
Integrating Fault Protection
The integrating fault protection feature allows the IC to
ignore transient overcurrent conditions for a program-
mable amount of time, giving the power-supply time to
behave like a current source to the load. This can hap-
pen, for example, under load-current transients when
the control loop requests maximum current to keep the
output voltage from going out of regulation. The ignore
time is programmed externally by connecting a capaci-
tor from FLTINT to GND. Under sustained overcurrent
faults, the voltage across this capacitor ramps up
toward the FLTINT shutdown threshold (2.7V, typ).
When V
FLTINT
reaches the shutdown threshold, the
power supply shuts down. A high-value bleed resistor
connected in parallel with the FLTINT capacitor allows
the capacitor to discharge toward the restart threshold
(1.9V, typ). FLTINT drops to the restart threshold allow-
ing for soft-starting the supply again.
The fault integration circuit works by forcing an 80礎
current into FLTINT for one clock cycle every time the
current-limit comparator ILIM (Figure 9) trips. Use the
following formula to calculate the approximate capaci-
tor needed for the desired shutdown time:
where I
FLTINT
is typically 80礎, and t
SH
is the desired
ignore time during which current-limit events from the
current-limit comparator are ignored.
This is an approximate formula; some testing may be
required to fine tune the actual value of the capacitor.
Calculate the approximate bleed resistor needed for
the desired recovery time using the following formula:
where t
RT
is the desired recovery time.
Choose t
RT
e 10 x t
SH
. Typical values for t
SH
can range
from a few hundred microseconds to a few milliseconds.
Shutdown
Shut down the controller section of the IC by driving
DCUVLO to GND using an open-collector or open-drain
transistor connected to GND. The DC-DC converter sec-
tion shuts down if REGOUT is below its DCUVLO level.
Current-Sense Comparator
The current-sense (CS) comparator and its associated
logic limit the peak current through the internal MOSFET.
Current is sensed at CS as a voltage across a sense
resistor between the source of the MOSFET and GND.
The power MOSFET switches off when the voltage at
CS reaches 156mV. Select the current-sense resistor,
R
SENSE
, according to the following equation:
R
SENSE
= 0.156V / I
LimPrimary
where I
LimPrimary
is the maximum peak primary-side
current.
To reduce switching noise, connect CS to an external
RC lowpass filter for additional filtering (Figure 3).
Applications Information
Design Example
Design Example 1: PD with three-output flyback DC-
DC converter
Figure 6 shows an isolated three-output flyback DC-DC
converter. It provides output voltages of 10V at 30mA,
5.1V at 1.8A, and 2.55V at 5.4A.
Design Example 2: PD with nonisolated step-down
(buck) converter
Figure 7 shows a buck converter with 12V, 0.75A out-
put. Caution: this converter does not have active cur-
rent limit.
t
C
FLTINT
RT
FLTINT
E
? 3514
.
C
I
t
FLTINT
FLTINT SH
E
?/DIV>
1 4
.
R
f C
C
In
V
V
V
RTCT
s RTCT
PCB
REGOUT
REGOUT
THRTCT
E
+
(
)
?/DIV>
?/DIV>
?/DIV>
?/DIV>
?/DIV>
?/DIV>
1
2
,
IEEE 802.3af PD Interface and PWM Controllers
with Integrated Power MOSFETs
18 ______________________________________________________________________________________
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相关代理商/技术参数 |
参数描述 |
|---|---|
| MAX5953BUTM+ | 功能描述:电压模式 PWM 控制器 IEEE 802.3af PD Int & PWM Controller RoHS:否 制造商:Texas Instruments 输出端数量:1 拓扑结构:Buck 输出电压:34 V 输出电流: 开关频率: 工作电源电压:4.5 V to 5.5 V 电源电流:600 uA 最大工作温度:+ 125 C 最小工作温度:- 40 C 封装 / 箱体:WSON-8 封装:Reel |
| MAX5953BUTM+T | 功能描述:电压模式 PWM 控制器 IEEE 802.3af PD Int & PWM Controller RoHS:否 制造商:Texas Instruments 输出端数量:1 拓扑结构:Buck 输出电压:34 V 输出电流: 开关频率: 工作电源电压:4.5 V to 5.5 V 电源电流:600 uA 最大工作温度:+ 125 C 最小工作温度:- 40 C 封装 / 箱体:WSON-8 封装:Reel |
| MAX5953CUTM+ | 功能描述:电压模式 PWM 控制器 IEEE 802.3af PD Int & PWM Controller RoHS:否 制造商:Texas Instruments 输出端数量:1 拓扑结构:Buck 输出电压:34 V 输出电流: 开关频率: 工作电源电压:4.5 V to 5.5 V 电源电流:600 uA 最大工作温度:+ 125 C 最小工作温度:- 40 C 封装 / 箱体:WSON-8 封装:Reel |
| MAX5953CUTM+T | 功能描述:电压模式 PWM 控制器 IEEE 802.3af PD Int & PWM Controller RoHS:否 制造商:Texas Instruments 输出端数量:1 拓扑结构:Buck 输出电压:34 V 输出电流: 开关频率: 工作电源电压:4.5 V to 5.5 V 电源电流:600 uA 最大工作温度:+ 125 C 最小工作温度:- 40 C 封装 / 箱体:WSON-8 封装:Reel |
| MAX5953DUTM+ | 功能描述:电压模式 PWM 控制器 IEEE 802.3af PD Int & PWM Controller RoHS:否 制造商:Texas Instruments 输出端数量:1 拓扑结构:Buck 输出电压:34 V 输出电流: 开关频率: 工作电源电压:4.5 V to 5.5 V 电源电流:600 uA 最大工作温度:+ 125 C 最小工作温度:- 40 C 封装 / 箱体:WSON-8 封装:Reel |
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