參數(shù)資料
型號(hào)： MAX1887
廠商： Maxim Integrated Products, Inc.
英文描述： Quick-PWM Slave Controllers for Multiphase, Step-Down
中文描述： Quick-PWM從控制器，用于多相、降壓型電源
文件頁(yè)數(shù)： 24/33頁(yè)
文件大?。?/td> 1018K
代理商： MAX1887
M
Input Capacitor Selection
The input capacitor must meet the ripple current
requirement (I
RMS
) imposed by the switching currents.
The MAX1887/MAX1897 multiphase slave controllers
operate out-of-phase (MAX1897 POL = V
CC
or float),
staggering the turn-on times of each phase. This mini-
mizes the input ripple current by dividing the load cur-
rent among independent phases:
for out-of-phase operation.
When operating the MAX1897 in-phase (POL = GND),
the high-side MOSFETs turn on simultaneously, so
input capacitors must support the combined input rip-
ple currents of each phase:
for in-phase operation.
For most applications, nontantalum chemistries (ceram-
ic, aluminum, or OS-CON) are preferred because of
their resistance to inrush surge currents typical of sys-
tems with a mechanical switch or connector in series
with the input. If the MAX1887/MAX1897 is operated as
the second stage of a two-stage power-conversion sys-
tem, tantalum input capacitors are acceptable. In either
configuration, choose an input capacitor that exhibits
less than +10
°
C temperature rise at the RMS input cur-
rent for optimal circuit longevity.
Power MOSFET Selection
Most of the following MOSFET guidelines focus on the
challenge of obtaining high load-current capability
when using high-voltage (>20V) AC adapters. Low-cur-
rent applications usually require less attention.
The high-side MOSFET (N
H
) must be able to dissipate
the resistive losses plus the switching losses at both
V
IN(MIN)
and V
IN(MAX)
. Calculate both of these sums.
Ideally, the losses at V
IN(MIN)
should be roughly equal
to losses at V
IN(MAX)
, with lower losses in between. If
the losses at V
IN(MIN)
are significantly higher than the
losses at V
IN(MAX)
, consider increasing the size of N
H
.
Conversely, if the losses at V
IN(MAX)
are significantly
higher than the losses at V
IN(MIN)
, consider reducing
the size of N
H
. If V
IN
does not vary over a wide range,
the minimum power dissipation occurs where the resis-
tive losses equal the switching losses.
Choose a low-side MOSFET that has the lowest possi-
ble on-resistance (R
DS(ON)
), comes in a moderate-
sized package (i.e., one or two SO-8s, DPAK or
D
2
PAK), and is reasonably priced. Make sure that the
DL gate driver can supply sufficient current to support
the gate charge and the current injected into the para-
sitic gate-to-drain capacitor caused by the high-side
MOSFET turning on; otherwise, cross-conduction prob-
lems may occur.
MOSFET Power Dissipation
Worst-case conduction losses occur at the duty factor
extremes. For the high-side MOSFET (N
H
), the worst-
case power dissipation due to resistance occurs at the
minimum input voltage:
Generally, a small high-side MOSFET is desired to
reduce switching losses at high input voltages.
However, the R
DS(ON)
required to stay within package
power-dissipation often limits how small the MOSFET
can be. Again, the optimum occurs when the switching
losses equal the conduction (R
DS(ON)
) losses. High-
side switching losses don
’
t usually become an issue
until the input is greater than approximately 15V.
Calculating the power dissipation of the high-side
MOSFET (N
H
) due to switching losses is difficult since it
must allow for difficult quantifying factors that influence
the turn-on and turn-off times. These factors include the
internal gate resistance, gate charge, threshold volt-
age, source inductance, and PC board layout charac-
teristics. The following switching-loss calculation
provides only a very rough estimate and is no substi-
tute for breadboard evaluation, preferably including
verification using a thermocouple mounted on N
H
:
=
(
where C
RSS
is the reverse transfer capacitance of N
H
and I
GATE
is the peak gate-drive source/sink current
(1A typ).
Switching losses in the high-side MOSFET can become
an insidious heat problem when maximum AC adapter
voltages are applied, due to the squared term in the C
V
IN
MOSFET chosen for adequate R
DS(ON)
at low battery
voltages becomes extraordinarily hot when biased from
2
fSW
switching-loss equation. If the high-side
PD N Switching
(
V
C
I
IN MAX
(
RSS SW LOAD
η
GATE
)
)
)
2
PD N
sistive
V
V
I
R
H
OUT
IN
LOAD
η
DS ON
(
(
Re
)
)
=
2
I
I
V
V
V
V
RMS
LOAD
OUT
IN
OUT
IN
=
(
)
I
I
V
V
V
V
RMS
LOAD
η
OUT
IN
OUT
IN
=
(
)
Quick-PWM Slave Controllers for
Multiphase, Step-Down Supplies
24
______________________________________________________________________________________
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參數(shù)描述
MAX1887EEE 功能描述:電流型 PWM 控制器 RoHS:否 制造商:Texas Instruments 開(kāi)關(guān)頻率:27 KHz 上升時(shí)間: 下降時(shí)間: 工作電源電壓:6 V to 15 V 工作電源電流:1.5 mA 輸出端數(shù)量:1 最大工作溫度:+ 105 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:TSSOP-14
MAX1887EEE+ 功能描述:電流型 PWM 控制器 CDMA Cellular/PCS System Power Supplies RoHS:否 制造商:Texas Instruments 開(kāi)關(guān)頻率:27 KHz 上升時(shí)間: 下降時(shí)間: 工作電源電壓:6 V to 15 V 工作電源電流:1.5 mA 輸出端數(shù)量:1 最大工作溫度:+ 105 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:TSSOP-14
MAX1887EEE+T 功能描述:電流型 PWM 控制器 CDMA Cellular/PCS System Power Supplies RoHS:否 制造商:Texas Instruments 開(kāi)關(guān)頻率:27 KHz 上升時(shí)間: 下降時(shí)間: 工作電源電壓:6 V to 15 V 工作電源電流:1.5 mA 輸出端數(shù)量:1 最大工作溫度:+ 105 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:TSSOP-14
MAX1887EEE-T 功能描述:電流型 PWM 控制器 RoHS:否 制造商:Texas Instruments 開(kāi)關(guān)頻率:27 KHz 上升時(shí)間: 下降時(shí)間: 工作電源電壓:6 V to 15 V 工作電源電流:1.5 mA 輸出端數(shù)量:1 最大工作溫度:+ 105 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:TSSOP-14
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