12V PWM Controller with Hot-Swap
______________________________________________________________________________________   21
quency is higher than f
LC
, but lower than the closed-
loop crossover frequency. The equations that define
the error amplifiers poles and zeroes (f
Z1
, f
Z2
, f
P1
, f
P2
,
and f
P3
) are the same as before. However, f
P2
is now
lower than the closed-loop crossover frequency. Figure
7 shows the error-amplifier feedback, as well as its gain
response for circuits that use higher ESR output capac-
itors (tantalum, aluminum electrolytic, etc.)
Pick a value for feedback resistor R5 in Figure 7 (values
between 1k& and 10k& are adequate). C7 is then cal-
culated as:
The circuit is implemented with C7 >> C8 and R3 >>
R6, in which case the error-amplifier gain between f
P2
and f
P3
is approximately equal to:
The modulator gain at f
C
is:
Since G
EA(fC)
x G
MOD(fC)
= 1, R6 can then be calculat-
ed as:
f
P2
is set to f
ZESR
. C6 is then calculated as:
R3 is then calculated as:
f
P3
is set at 5xf
C
. Therefore, C8 is calculated as:
Hot-Swap Controller
Applications Information
Additional External Gate Capacitance
External capacitance can be added from the gate of the
external MOSFET to AGND to reduce the dv/dt of the
PWM controller input voltage (V
PWM_IN
), decreasing the
hot-swap inrush current. Add a 10k& resistor in series
with the added gate capacitor to prevent degrading the
device turn-off response to a fault condition.
Layout Considerations
To take advantage of the switch response time to an
output fault condition, it is important to keep all traces as
short as possible and to maximize the high-current trace
width to reduce the effect of undesirable parasitic
inductance. Use a ground plane to minimize impedance
and inductance. Minimize the trace length that connects
to IN and HSENSE (< 10mm), and ensures accurate
current sensing with Kelvin connections.
When the output is short circuited, the voltage drop
across the external MOSFET becomes large. Hence,
the power dissipation in the switch increases, as does
the die temperature. An efficient way to achieve good
power dissipation on a surface-mount package is to lay
out two copper pads directly under the MOSFET pack-
age on both sides of the board. Connect the two pads
to the ground plane through vias, and use enlarged
copper mounting pads on the top side of the board.
PWM Controller
Applications Information
Power Dissipation
The 32-pin TQFN thermally enhanced package can dis-
sipate 2.7W. Calculate power dissipation in the
MAX5950 as a product of the input voltage and the
total REG output current (I
REG
). I
REG
includes quies-
cent current (I
Q
) and gate-drive current (I
DREG
):
P
D
= V
IN
x I
REG
I
REG
= I
Q
+ [f
SW
x (Q
G1
+ Q
G2
)]
where Q
G1
and Q
G2
represent the total gate charge of
the low-side and high-side external MOSFETs, f
SW
is the
switching frequency of the converter, and I
Q
is the quies-
cent current of the device at the switching frequency.
Use the following equation to calculate the maximum
power dissipation (P
DMAX
) in the chip at a given ambi-
ent temperature (T
A
):
P
DMAX
= 34.5 x (150 - T
A
)&&&.mW
C
R
f
C
8
1
2
5  5
=
?nbsp  ?nbsp ?/DIV>
?/DIV>
R
f
C
LC
3
1
2
6
H
?nbsp   ?/DIV>
?/DIV>
C
ESR
R
OUT
6
6
=
?/DIV>
R
R   G
L  C
f
MOD DC
OUT
C
6
5
2
2
2
H
?/DIV>
?nbsp ?/DIV>
?/DIV>
(    )
(   )
?/DIV>
G
G
L  C
f
MOD fC
MOD DC
OUT    C
(   )
(    )
(   )
=
?nbsp ?/DIV>
?/DIV>
2
2
2
?/DIV>
R
R
5
f
R
LC
7
1
2    0 5
5
=
?nbsp   ?nbsp   ?/DIV>
?nbsp  .
相關代理商/技術參數 |
參數描述 |
MAX5950ETJ+ |
功能描述:電壓模式 PWM 控制器 12V PWM Controller w/Hot-Swap RoHS:否 制造商:Texas Instruments 輸出端數量:1 拓撲結構:Buck 輸出電壓:34 V 輸出電流: 開關頻率: 工作電源電壓:4.5 V to 5.5 V 電源電流:600 uA 最大工作溫度:+ 125 C 最小工作溫度:- 40 C 封裝 / 箱體:WSON-8 封裝:Reel |
MAX5950ETJ+T |
功能描述:電壓模式 PWM 控制器 12V PWM Controller w/Hot-Swap RoHS:否 制造商:Texas Instruments 輸出端數量:1 拓撲結構:Buck 輸出電壓:34 V 輸出電流: 開關頻率: 工作電源電壓:4.5 V to 5.5 V 電源電流:600 uA 最大工作溫度:+ 125 C 最小工作溫度:- 40 C 封裝 / 箱體:WSON-8 封裝:Reel |
MAX5950ETJ-T |
功能描述:電壓模式 PWM 控制器 RoHS:否 制造商:Texas Instruments 輸出端數量:1 拓撲結構:Buck 輸出電壓:34 V 輸出電流: 開關頻率: 工作電源電壓:4.5 V to 5.5 V 電源電流:600 uA 最大工作溫度:+ 125 C 最小工作溫度:- 40 C 封裝 / 箱體:WSON-8 封裝:Reel |
MAX5950EVKIT |
制造商:Maxim Integrated Products 功能描述:12V PWM CONTROLLER WITH HOT-SWAP - Rail/Tube |
MAX5951ETJ |
功能描述:電壓模式 PWM 控制器 RoHS:否 制造商:Texas Instruments 輸出端數量:1 拓撲結構:Buck 輸出電壓:34 V 輸出電流: 開關頻率: 工作電源電壓:4.5 V to 5.5 V 電源電流:600 uA 最大工作溫度:+ 125 C 最小工作溫度:- 40 C 封裝 / 箱體:WSON-8 封裝:Reel |
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