參數(shù)資料
型號： MAX1777
廠商： Maxim Integrated Products, Inc.
英文描述： High-Efficiency, Quad Output, Main Power- Supply Controllers for Notebook Computers
中文描述： 高效率、四路輸出、主電源控制器，用于筆記本電腦
文件頁數(shù)： 19/32頁
文件大?。?/td> 497K
代理商： MAX1777
M
High-Effic ienc y, Quad Output, Main Power-
S upply Controllers for Notebook Computers
______________________________________________________________________________________
19
tinuous and discontinuous inductor-current operation
(also known as the critical conduction point):
where K is the on-time scale factor (see the
On-Time
One-Shot (t
ON
)
section). The load-current level at which
PFM/PWM crossover occurs, I
LOAD(SKIP)
, is equal to 1/2
the peak-to-peak ripple current, which is a function of the
inductor value (Figure 5). For example, in the MAX1777
typical application circuit with V
OUT2
= 5V, V+ = 12V,
L = 7.6μH, and K = 5μs, switchover to pulse-skipping
operation occurs at I
LOAD
= 0.96A or about 1/5 full load.
The crossover point occurs at an even lower value if a
swinging (soft-saturation) inductor is used.
The switching waveforms may appear noisy and asyn-
chronous when light loading causes pulse-skipping
operation, but this is a normal operating condition that
results in high light-load efficiency. Trade-offs in PFM
noise vs. light-load efficiency are made by varying the
inductor value. Generally, low inductor values produce
a broader efficiency vs. load curve, while higher values
result in higher full-load efficiency (assuming that the
coil resistance remains fixed) and less output voltage
ripple. Penalties for using higher inductor values
include larger physical size and degraded load-tran-
sient response (especially at low input voltage levels).
DC output accuracy specifications refer to the trip level of
the error comparator. When the inductor is in continuous
conduction, the output voltage has a DC regulation high-
er than the trip level by 50% of the ripple. In discontinu-
ous conduction (
SKIP
= GND, light load), the output
voltage has a DC regulation higher than the trip level by
approximately 1.5% due to slope compensation.
Forc ed-PWM Mode
The low-noise, forced-PWM (
SKIP
= V
CC
) mode dis-
ables the zero-crossing comparator, which controls the
low-side switch on-time. Disabling the zero-crossing
detector causes the low-side, gate-drive waveform to
become the complement of the high-side, gate-drive
waveform. The inductor current reverses at light loads
as the PWM loop strives to maintain a duty ratio of
V
OUT
/V+. The benefit of forced-PWM mode is to keep
the switching frequency fairly constant, but it comes at
a cost: the no-load battery current can be 10mA to
50mA, depending on switching frequency and the
external MOSFETs.
Forced-PWM mode is most useful for reducing audio-
frequency noise, improving load-transient response,
providing sink-current capability for dynamic output
voltage adjustment, and improving the cross-regulation
of multiple-output applications that use a flyback trans-
former or coupled inductor.
Minimum 25kHz Pulse-S kipping Mode
(Ultrasonic Mode)
Leaving
SKIP
unconnected or connecting
SKIP
to REF
activates a pulse-skipping mode with a minimum
switching frequency of 25kHz. This ultrasonic pulse-
skipping mode reduces audio-frequency modulation of
the power supply that may occur in Idle Mode at very
light loads. The transition to fixed-frequency PWM oper-
ation is automatic and occurs at the same point as in
Idle Mode. Ultrasonic pulse skipping occurs if no
switching has taken place within the last 28μs. DL_
turns on to induce a regulated negative current in the
inductor. DH_ turns on when the inductor current
reaches the regulated negative current limit. Starting
with a DL_ pulse greatly reduces the ripple current
when compared to starting with a DH_ pulse (Idle
Mode). The output voltage level determines the nega-
tive current limit.
Calculate the negative ultrasonic current-limit threshold
with the following equation:
where V
FB
> V
REF
, and R
ON
is the on-resistance of the
synchronous rectifier (MAX1999) or the current-sense
resistor value (MAX1777/MAX1977).
V
I
R
V
V
V
V
NEG
LX
ON
REF
FB
ILIM
S
U
=
×
=
×
(
)
.
_
0 467
I
K
V
2
L
V
V
+
V
LOAD SKIP
OUT
×
OUT
(
)
_
_
=
×
+
I
I
LOAD
= I
PEAK
/2
ON-TIME
0
TIME
-I
PEAK
L
V+
- V
OUT
i
t
=
Figure 5. Pulse- Skipping/Discontinuous Crossover Point
相關(guān)PDF資料
PDF描述
MAX1777-MAX1999 High-Efficiency, Quad Output, Main Power- Supply Controllers for Notebook Computers
MAX1977 High-Efficiency, Quad Output, Main Power- Supply Controllers for Notebook Computers
MAX1999 High-Efficiency, Quad Output, Main Power- Supply Controllers for Notebook Computers
MAX1977EEI High-Efficiency, Quad Output, Main Power- Supply Controllers for Notebook Computers
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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
MAX1777EEI 功能描述:DC/DC 開關(guān)控制器 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風(fēng)格: 封裝 / 箱體:CPAK
MAX1777EEI+ 功能描述:DC/DC 開關(guān)控制器 Quad-Out Main Power Sply Ctlr for Ntbk RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風(fēng)格: 封裝 / 箱體:CPAK
MAX1777EEI+T 功能描述:DC/DC 開關(guān)控制器 Quad-Out Main Power Sply Ctlr for Ntbk RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風(fēng)格: 封裝 / 箱體:CPAK
MAX1777EEI-T 功能描述:DC/DC 開關(guān)控制器 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風(fēng)格: 封裝 / 箱體:CPAK
MAX1778EUG 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT
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