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參數(shù)資料
| 型號： | MAX1791 |
| 廠商： | Maxim Integrated Products, Inc. |
| 英文描述： | High-Efficiency, 10-Pin レMAX, Step-Down Controllers for Notebooks |
| 中文描述： | 高效率、10引腳µMAX、降壓型控制器，用于筆記本電腦 |
| 文件頁數(shù)： | 12/20頁 |
| 文件大小： | 391K |
| 代理商： | MAX1791 |
M
High-Efficiency, 10-Pin μMAX, Step-Down
Controllers for Notebooks
12
______________________________________________________________________________________
Overdriving the VL regulator with an external 5V supply
also increases the MAX1762/MAX1791s
’
efficiency.
The MAX1762/MAX1791 include an input undervoltage
lockout (UVLO) circuit that prevents the device from
switching until VL > 4.4V (max). UVLO ensures there is
a sufficient drive for the external MOSFETs, prevents
the high-side MOSFET from being turned on for near
100% duty cycle, and keeps the output in regulation.
Voltage Reference (REF)
The 2V reference (REF) is accurate to ±1% over tem-
perature, making REF useful as a precision system ref-
erence. Bypass REF to GND with a 0.1μF (min) ceramic
capacitor. REF can supply up to 50μA for external
loads. However, if tight-accuracy specs for either V
OUT
or REF are essential, avoid loading REF. Loading slight-
ly reduces the main output voltage by an amount that
tracks the reference-voltage load regulation error.
Free-Running Constant On-Time PWM
Controller with Input Feed-Forward
The PWM control architecture is a quasi-fixed-frequen-
cy constant on-time current-mode type with voltage
feed-forward. This architecture relies on the output rip-
ple voltage to provide the PWM ramp signal; thus, the
output filter capacitor
’
s ESR acts as a feedback resis-
tor. The control algorithm is very simple. The high-side
switch on-time is determined solely by a one-shot
whose period is inversely proportional to input voltage
and directly proportional to output voltage. There is
another one-shot that sets a minimum amount of off-
time (500ns max). The on-time one-shot triggers when
all of the following conditions are met: the error com-
parator 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
The on-time of the one-shot is inversely proportional to
the battery voltage as measured by the VP input, and
directly proportional to the output voltage sensed at
OUT:
×
(
K
where K is internally fixed at 3.349μs, and 0.075V is a
factor that accounts for the expected drop across the
synchronous switch. This arrangement maintains a
switching frequency that is nearly constant as V
BATT
,
I
LOAD
, and V
OUT
are changed. Table 3 shows the oper-
ating frequency range for the MAX1762/MAX1791.
Note that the output voltage adjust range for continu-
ous-conduction operation is restricted by the non-
adjustable 0.5μs (max) minimum off-time. Worst-case
dropout performance is determined by the minimum
on-time spec. The worst-case duty factor limit is:
t
ON MIN
with V
BATT
= 6V and V
OUT
= 5V. Therefore, with IR volt-
age drops in the loop included, the minimum input volt-
age to achieve V
OUT
= 5V is about 6.1V, using the
step-down transfer function equation for duty cycle (DC
= V
OUT
/V
IN
). Typical units exhibit better performance.
Note that transient response is somewhat degraded
near dropout, and the circuit may need additional bulk
output capacitance to support fast load changes.
Automatic Pulse-Skipping Switchover
This PWM control algorithm automatically switches over
to pulse-skipping operation at light loads. The
MAX1762/MAX1791 truncates the low-side switch
’
s on-
time when the inductor current drops to zero. The load
current level at which pulse-skipping/PWM crossover
occurs is equal to 1/2 the peak-to-peak ripple current,
which is a function of the inductor value (Figure 6).
The inductor current is never allowed to go negative. If
the output voltage is above its regulation point and the
inductor current reaches zero, the low-side driver is
switched off. Once the output voltage falls below its
regulation point, the high-side driver is switched on.
This causes a dead time in between when the high-
side and low-side drivers are on, skipping pulses and
resulting in the switching frequency slowing at light
loads, thereby improving efficiency.
MOSFET Gate Drivers
The DH and DL drivers are optimized for driving moder-
ate-size power MOSFETs. This is consistent with the
low duty factor seen in the notebook CPU environment
where a large V
BATT
- V
OUT
differential exists. The high-
side driver (DH) is rated for 0.6A source/sink capability
and swings from VP to GND. The low-side driver (DL) is
I
K
V
2L
V
-V
V
LOAD(SKIP)
OUT
VP
OUT
VP
=
×
t
t
ON MIN
OFF MAX
)
)
)
=
=
+
2.55 s
2.55 s+0.5 s
84%
t
V
+0.075V
V
ON
OUT
BATT
=
)
Table 3. Operating Frequency
DEVICE
K
(
μ
s)
3.349
MIN
(kHz)
268.7
TYP
(kHz)
298.5
MAX
(kHz)
328
MAX1762/MAX1791
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| MAX1762 | Replaced by TMS320VC5506 : Digital Signal Processor 100-LQFP |
| MAX1762-MAX1791 | High-Efficiency, 10-Pin レMAX, Step-Down Controllers for Notebooks |
| MAX1762EUB | Replaced by TMS320C2802 : 16-bit, 5V fixed point DSP 132-BQFP -40 to 125 |
| MAX1791EUB | High-Efficiency, 10-Pin レMAX, Step-Down Controllers for Notebooks |
| MAX1792 | 500mA Low-Dropout Linear Regulator in レMAX |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| MAX17911EVKIT+ | 制造商:Maxim Integrated Products 功能描述:EVKIT - Boxed Product (Development Kits) |
| MAX17911GTL+ | 制造商:Maxim Integrated Products 功能描述:AMD SVI1 CPU CONTROLLER 3PHASE - Rail/Tube |
| MAX1791EUB | 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 |
| MAX1791EUB+ | 功能描述:DC/DC 開關(guān)控制器 Step-Down for Notebook 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 |
| MAX1791EUB+ | 制造商:Maxim Integrated Products 功能描述:CONTROLLER ((NW)) |
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