參數(shù)資料
型號(hào)： MAX1717
廠商： Maxim Integrated Products, Inc.
元件分類： 數(shù)字信號(hào)處理
英文描述： Replaced by TMS320VC5506 : Digital Signal Processors 132-BQFP
中文描述： 動(dòng)態(tài)可調(diào)、同步降壓型控制器，用于筆記本CPU
文件頁數(shù)： 29/32頁
文件大小： 501K
代理商： MAX1717
M
Dynamically Adjustable, Synchronous
Step-Down Controller for Notebook CPUs
______________________________________________________________________________________
29
as much as it ramps up during the on-time (
I
UP
). The
ratio h =
I
UP
/
I
DOWN
is an indicator of ability to slew
the inductor current higher in response to increased
load, and must always be greater than 1. As h
approaches 1, the absolute minimum dropout point, the
inductor current will be less able to increase during
each switching cycle and V
SAG
will greatly increase
unless additional output capacitance is used.
A reasonable minimum value for h is 1.5, but this may
be adjusted up or down to allow tradeoffs between
V
SAG
, output capacitance, and minimum operating
voltage. For a given value of h, the minimum operating
voltage can be calculated as:
(
where V
DROP1
and V
DROP2
are the parasitic voltage
drops in the discharge and charge paths (see On-Time
One-Shot), T
OFF(MIN)
is from the
Electrical Character-
istics
table, and K is taken from Table 3. The absolute
minimum input voltage is calculated with h = 1.
If the calculated V
IN(MIN)
is greater than the required
minimum input voltage, then operating frequency must
be reduced or output capacitance added to obtain an
acceptable V
SAG
. If operation near dropout is anticipat-
ed, calculate V
SAG
to be sure of adequate transient
response.
Dropout Design Example:
V
OUT
= 1.6V
fsw = 550kHz
K = 1.8μs, worst-case K = 1.58μs
T
OFF(MIN)
= 500ns
V
DROP1
= V
DROP2
= 100mV
h = 1.5
V
IN(MIN)
= (1.6V + 0.1V) / (1-0.5μs
·
1.5/1.58μs) + 0.1V
- 0.1V = 3.2V
Calculating again with h = 1 gives the absolute limit of
dropout:
V
IN(MIN)
= (1.6V + 0.1V) / (1-1.0
0.5μs/1.58μs) - 0.1V
+ 0.1V = 2.5V
Therefore, V
IN
must be greater than 2.5V, even with very
large output capacitance, and a practical input voltage
with reasonable output capacitance would be 3.2V.
Adjusting V
OUT
with a Resistor-Divider
The output voltage can be adjusted with a resistor-
divider rather than the DAC if desired (Figure 11). The
drawback is that the on-time doesn’t automatically
receive correct compensation for changing output voltage
levels. This can result in variable switching frequency
as the resistor ratio is changed, and/or excessive
switching frequency. The equation for adjusting the output
voltage is:
where V
FB
is the currently selected DAC value, and
R
INT
is the FB input resistance. When using external
resistors, FBS remote sensing is not recommended, but
GNDS remote sensing is still possible. Connect FBS to
FB, and GNDS to a remote ground location. In resistor-
adjusted circuits, the DAC code should be set as close
as possible to the actual output voltage in order to mini-
mize the shift in switching frequency.
Adjusting V
OUT
Above 2V
The feed-forward circuit that makes the on-time depen-
dent on battery voltage maintains a nearly constant
switching frequency as V
IN
, I
LOAD
, and the DAC code
are changed. This works extremely well as long as FB
is connected directly to the output. When the output is
adjusted with a resistor divider, the switching frequency
is increased by the inverse of the divider ratio.
This change in frequency can be compensated with the
addition of a resistor-divider to the battery-sense input
(V+). Attach a resistor-divider from the battery voltage
to V+ on the MAX1717, with the same attenuation factor
as the output divider. The V+ input has a nominal input
impedance of 600k
, which should be considered
when selecting resistor values.
One-Stage (Battery Input) vs. Two-Stage
(5V Input) Applications
The MAX1717 can be used with a direct battery connec-
tion (one stage) or can obtain power from a regulated 5V
supply (two stage). Each approach has advantages,
and careful consideration should go into the selection of
the final design.
The one-stage approach offers smaller total inductor
size and fewer capacitors overall due to the reduced
demands on the 5V supply. The transient response of
the single stage is better due to the ability to ramp the
inductor current faster. The total efficiency of a single
stage is better than the two-stage approach.
V
V
R
R
R
OUT
FB
INT
=
+
1
1
2
V
V
V
T
x h
)
K
V
V
IN MIN
(
OUT
DROP
OFF MIN
(
DROP
DROP
)
+
=
+
)
1
2
1
1
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參數(shù)描述
MAX17175ETG+ 制造商:Maxim Integrated Products 功能描述:BOOST REG W/INTEGRATED CHARGE PUMPS SWITCH CONTROL & HIGH-CU - Rail/Tube
MAX1717BEEG 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
MAX1717BEEG+ 功能描述:DC/DC 開關(guān)控制器 Adj Synchronous Step-Down 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
MAX1717BEEG+T 功能描述:DC/DC 開關(guān)控制器 Adj Synchronous Step-Down 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
MAX1717BEEG-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
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