參數(shù)資料
型號： MAX1977
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)： 18/32頁
文件大?。?/td> 497K
代理商： MAX1977
M
High-Effic ienc y, Quad Output, Main Power-
S upply Controllers for Notebook Computers
18
______________________________________________________________________________________
These internal blocks are not powered directly from the
battery. Instead, the 5V (LDO5) linear regulator steps
down the battery voltage to supply both internal circuit-
ry and the gate drivers. The synchronous-switch gate
drivers are directly powered from LDO5, while the high-
side switch gate drivers are indirectly powered from
LDO5 through an external diode-capacitor boost cir-
cuit. An automatic bootstrap circuit turns off the 5V lin-
ear regulator and powers the device from OUT5 when
OUT5 is above 4.56V.
Free-Running, Constant On-T ime PWM
Controller with Input Feed Forward
The Quick-PWM control architecture is a pseudo-fixed-
frequency, constant on-time, current-mode type with
voltage feedforward. The Quick-PWM control architec-
ture relies on the output ripple voltage to provide the
PWM ramp signal, thus the output filter capacitor’s ESR
acts as a current-feedback resistor. The high-side
switch on-time is determined by a one-shot whose peri-
od is inversely proportional to input voltage and directly
proportional to output voltage. Another one-shot sets a
minimum off-time (300ns typ). The on-time one-shot
triggers when the following conditions are met: the error
comparator is low, the synchronous rectifier current is
below the current-limit threshold, and the minimum off-
time one-shot has timed out.
On-T ime One-S hot (t
ON
)
Each PWM core includes a one-shot that sets the high-
side switch on-time for each controller. Each fast, low-
jitter, adjustable one-shot includes circuitry that varies
the on-time in response to battery and output voltage.
The high-side switch on-time is inversely proportional to
the battery voltage as measured by the V+ input, and
proportional to the output voltage. This algorithm results
in a nearly constant switching frequency despite the
lack of a fixed-frequency clock generator. The benefit
of a constant switching frequency is the frequency can
be selected to avoid noise-sensitive frequency regions:
t
ON
= K (V
OUT
+ 0.075V) / V+
See Table 2 for approximate K-factors. The constant
0.075V is an approximation to account for the expected
drop across the synchronous-rectifier switch. Switching
frequency increases as a function of load current due
to the increasing drop across the synchronous rectifier,
which causes a faster inductor-current discharge ramp.
On-times translate only roughly to switching frequen-
cies. The on-times guaranteed in the
Electrical
Characteristics
are influenced by switching delays in
the external high-side power MOSFET. Also, the dead-
time effect increases the effective on-time, reducing the
switching frequency. It occurs only in PWM mode (
SKIP
= V
CC
) and during dynamic output voltage transitions
when the inductor current reverses at light or negative
load currents. With reversed inductor current, the
inductor’s EMF causes LX to go high earlier than nor-
mal, extending the on-time by a period equal to the DH-
rising dead time.
For loads above the critical conduction point, the actual
switching frequency is:
where V
DROP1
is the sum of the parasitic voltage drops
in the inductor discharge path, including synchronous
rectifier, inductor, and PC board resistances; V
DROP2
is
the sum of the parasitic voltage drops in the charging
path, including high-side switch, inductor, and PC
board resistances, and t
ON
is the on-time calculated by
the MAX1777/MAX1977/MAX1999.
Automatic Pulse-S kipping S witc hover
(Idle Mode)
In Idle Mode (
SKIP
= GND), an inherent automatic
switchover to PFM takes place at light loads. This
switchover is affected by a comparator that truncates
the low-side switch on-time at the inductor current’s
zero crossing. This mechanism causes the threshold
between pulse-skipping PFM and nonskipping PWM
operation to coincide with the boundary between con-
f
V
V
t
V
V
OUT
(
DROP
ON
DROP
=
+
+ +
)
1
2
SMPS
SWITCHING
FREQUENCY (kHz)
200
300
400
500
K-FACTOR (μs)
APPROXIMATE K-
FACTOR ERROR (%)
±10
±10
±10
±10
MAX1777/MAX1999 (t
ON
= V
CC
), 5V
MAX1777/MAX1999 (t
ON
= V
CC
), 3.3V
MAX1977/MAX1999 (t
ON
= GND), 5V
MAX1977/MAX1999 (t
ON
= GND), 3.3V
5.0
3.3
2.5
2.0
Table 2. Approximate K-Factor Errors
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相關代理商/技術(shù)參數(shù)
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MAX1977EEI 功能描述:DC/DC 開關控制器 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關頻率: 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 安裝風格: 封裝 / 箱體:CPAK
MAX1977EEI+ 功能描述:DC/DC 開關控制器 Quad Out Main Power Supply Controller RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關頻率: 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 安裝風格: 封裝 / 箱體:CPAK
MAX1977EEI+T 功能描述:DC/DC 開關控制器 Quad Out Main Power Supply Controller RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關頻率: 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 安裝風格: 封裝 / 箱體:CPAK
MAX1977EEI-T 功能描述:DC/DC 開關控制器 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關頻率: 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 安裝風格: 封裝 / 箱體:CPAK
MAX1977EEI-TG068 制造商:Rochester Electronics LLC 功能描述: 制造商:Maxim Integrated Products 功能描述:
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