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參數(shù)資料
| 型號： | MAX1994ETM |
| 廠商： | MAXIM INTEGRATED PRODUCTS INC |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | Dual Step-Down Controllers Plus Linear- Regulator Controller for Notebook Computers |
| 中文描述： | DUAL SWITCHING CONTROLLER, 1000 kHz SWITCHING FREQ-MAX, CQCC48 |
| 封裝： | 7 X 7 MM, 0.80 MM HEIGHT, THIN, QFN-48 |
| 文件頁數(shù)： | 25/49頁 |
| 文件大?。?/td> | 983K |
| 代理商： | MAX1994ETM |
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M
Dual Step-Down Controllers Plus Linear-
Regulator Controller for Notebook Computers
______________________________________________________________________________________
25
Free-Running, Constant On-Time PWM
Controller with Input Feed-Forward
Both BUCK1 and BUCK2 employ Maxim
’
s proprietary
Quick-PWM control architecture. The control scheme is
a pseudo fixed-frequency, constant-on-time current-
mode type with voltage feed forward (Figures 3, 4, and
5). It relies on the output ripple voltage to provide the
PWM ramp signal. This signal can come from the out-
put filter capacitor
’
s ESR or a dedicated sense resistor.
The control algorithm is simple: the high-side switch on-
time is determined solely by a one-shot whose period is
inversely proportional to input voltage and directly pro-
portional to output voltage. Another one-shot sets a
minimum off-time (425ns, typ). The on-time one-shot is
triggered if the error comparator is low, the low-side
switch current is below the current-limit threshold, and
the minimum off-time one-shot has timed out.
On-Time One-Shot (TON)
The heart of the PWM core is the one-shot that sets the
high-side switch on-time (Figures 4 and 5). This fast,
low-jitter, adjustable one-shot includes circuitry that
varies the on-time in response to battery and output
voltages. The high-side switch on-time is inversely pro-
portional to the battery voltage as measured by the V+
input, and proportional to the output voltage. This algo-
rithm results in a nearly constant switching frequency
despite the lack of a fixed-frequency clock generator.
The benefits of a constant switching frequency are
twofold: first, the frequency can be selected to avoid
noise-sensitive regions such as the 455kHz IF band;
second, the inductor ripple-current operating point
remains relatively constant, resulting in easy design
methodology and predictable output-voltage ripple:
On-Time = K (V
OUT
+ 0.075V) / V
IN
where K is set by the TON pin-strap connection and
0.075V is an approximation to accommodate for the
expected drop across the low-side MOSFET switch
(Table 3).
The on-times for BUCK1 have nominal frequency set-
tings of 200kHz, 300kHz, 550kHz, or 1000kHz, while the
on-times for BUCK2 are shifted to minimize beating
between the two regulators. The corresponding fre-
quency settings for BUCK2 are 260kHz, 390kHz,
390kHz, and 715kHz. The BUCK2 on-times for TON =
open and TON = V
CC
are shifted down to improve the
efficiency. The BUCK2 on-times for TON = GND and
TON = REF are shifted up to avoid beating, yet maintain
the efficiency. The latter settings were not shifted down
because the resulting frequencies would be too high.
The on-time one-shot has good accuracy at the operat-
ing points specified in the
Electrical Characteristics
(
±
10% at 200kHz and 300kHz,
±
12.5% at 550kHz and
1000kHz for BUCK1). On-times at operating points far
removed from the conditions specified in the
Electrical
Characteristics
can vary over a wider range.
For example, the 1000kHz setting typically runs about
10% slower with inputs much greater than 5V due to the
very short on-times required.
On-times translate only roughly to switching frequencies.
The on-times guaranteed in the
Electrical Characteristics
are influenced by switching delays in the external high-
side MOSFETs. Resistive losses, including the inductor,
both MOSFETs, output capacitor ESR, and PC board
copper losses tend to raise the switching frequency at
higher output currents. Also, the dead-time effect
increases the effective on-time, reducing the switching
frequency. It occurs only in PWM mode (SKP_/
SDN
=
open) and during dynamic output-voltage transitions
(BUCK1) 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
normal, extending the on-time by a period equal to the
DH_ low-to-high dead time.
Table 3. Approximate K-Factor Errors
TON
BUCK1
K-FACTOR
(μs)
BUCK1
FREQUENCY
(kHz)
BUCK1
K-FACTOR ERROR
(%)
BUCK2
K-FACTOR
(μs)
BUCK2
FREQUENCY
(kHz)
BUCK2
K-FACTOR
ERROR (%)
GND
Open
REF
V
CC
1.0
1.8
3.3
5.0
1000
550
300
200
±
12.5
±
12.5
±
10
±
10
1.4
2.56
2.56
3.84
715
390
390
260
±
12.5
±
10
±
10
±
10
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
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| MAX1994ETM+ | 功能描述:DC/DC 開關(guān)控制器 Integrated Circuits (ICs) 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 安裝風格: 封裝 / 箱體:CPAK |
| MAX1994ETM+T | 功能描述:DC/DC 開關(guān)控制器 Integrated Circuits (ICs) 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 安裝風格: 封裝 / 箱體:CPAK |
| MAX1994ETM-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 安裝風格: 封裝 / 箱體:CPAK |
| MAX1994EVKIT | 功能描述:DC/DC 開關(guān)控制器 Evaluation Kit for the MAX1816 MAX1980 MAX1994 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 安裝風格: 封裝 / 箱體:CPAK |
| MAX1995EGI | 功能描述:顯示驅(qū)動器和控制器 RoHS:否 制造商:Panasonic Electronic Components 工作電源電壓:2.7 V to 5.5 V 最大工作溫度: 安裝風格:SMD/SMT 封裝 / 箱體:QFN-44 封裝:Reel |
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