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參數(shù)資料
| 型號： | LM3370TLX-3008 |
| 廠商： | National Semiconductor Corporation |
| 元件分類： | DC/DC變換器 |
| 英文描述： | Dual Synchronous Step-Down DC-DC Converter with Dynamic Voltage Scaling Function |
| 中文描述： | 雙同步降壓型DC - DC轉(zhuǎn)換器的動態(tài)電壓調(diào)節(jié)功能 |
| 文件頁數(shù)： | 21/26頁 |
| 文件大?。?/td> | 5302K |
| 代理商： | LM3370TLX-3008 |
Application Information
SETTING OUTPUT VOLTAGE VIA I
2
C Compatible
The outputs of the LM3370 can be programmed through Buck
1 & Buck 2 registers via I
2
C. Buck 1 output voltage can be
dynamically adjusted between 1V to 2V in 50 mV steps and
Buck 2 output voltage can be adjusted between 1.8V to 3.3V
in 100 mV steps. Finer adjustments to the output of Buck 2
can be achieved with the placement of a resistor betweeen
VOUT2 and the FB2 pin. Typically by placing a 20K
resistor,
R, between these nodes will result in the programmed Output
Voltage increasing by approximately 45mV,
Δ
V
TYP
.
Δ
V
TYP
= R × 500mV / 234K
Please refer to for programming the desire output voltage. If
the I
2
C compatible feature is not used, the default output volt-
age will be the pre-trimmed voltage. For example,
LM3370SD-3021 refers to 1.2V for Buck 1 and 3.3V for Buck
2.
V
DD
Pin
V
is the power supply to the internal control circuit, if V
DD
pin is not tied to V
during normal operating condition, V
DD
must be set equal or greater of the two inputs ( V
IN1
or V
IN2
An optional capacitor can be used for better noise immunity
at V
pin or when V
is not tied to either V
pins. Addition-
ally, for reasons of noise suppression, it is advisable to tie the
EN1/EN2 pins to V
DD
rather than V
IN
.
SDA, SCL Pins
When not using I
2
C the SDA and SCL pins should be tied
directly to the V
DD
pin.
Micro-Stepping:
The Micro-Stepping feature minimizes output voltage over-
shoot/undershoot during large output transients. If Micro-
stepping is enabled through I
2
C, the output voltage automat-
ically ramps at 50 mV per step for Buck 1 and 100 mV per
step for Buck 2. The steps are summarized as follow:
Buck 1: 50 mV/step and 32 μs/step
Buck 2: 100 mV/step and 32 μs/step
For example if changing Buck 1 voltage from 1V to 1.8V yields
20 steps [(1.8 - 1)/ 0.05 = 20]. This translates to 640
μ
s [(20 x
32 μs) = 640 μs] needed to reach the final target voltage.
INDUCTOR SELECTION
There are two main considerations when choosing an induc-
tor; the inductor should not saturate, and the inductor current
ripple is small enough to achieve the desired output voltage
ripple.
There are two methods to choose the inductor current rating.
method 1:
The total current is the sum of the load and the inductor ripple
current. This can be written as
I
LOAD
load current
V
IN
input voltage
L inductor
f switching frequency
method 2:
A more conservative approach is to choose an inductor that
can handle the maximum current limit of 1400 mA.
Given a peak-to-peak current ripple (I
PP
) the inductor needs
to be at least
A 2.2 μH inductor with a saturation current rating of at least
1400 mA is recommended for most applications. The
inductor’s resistance should be less than around 0.2
for
good efficiency.
Table 2
lists suggested inductors and sup-
pliers.
For low-cost applications, an unshielded bobbin inductor is
suggested. For noise critical applications, a toroidal or shield-
ed-bobbin inductor should be used. A good practice is to lay
out the board with overlapping footprints of both types for de-
sign flexibility. This allows substitution of a low-noise toroidal
inductor, in the event that noise from low-cost bobbin models
is unacceptable.
Below are some suggested inductor manufacturers include
but are not limited to:
TABLE 2. Suggested Inductors and Suppliers
Model
Vendor
Dimensions
(mm)
3.3 x 3.3 x 1.4
3.3 x 3.3 x 1.0
3.1 x 3.1 x 1.4
3.0 x 3.0 x 1.0
3.0 x 3.0 x 1.5
2.6 x 2.8 x 1.0
I
SAT
DO3314-222
LPO3310-222
SD3114-2R2
NR3010T2R2M
NR3015T2R2M
VLF3010AT-
2R2M1R0
Coilcraft
1.6A
1.1A
1.48A
1.1A
1.48A
1.0A
Cooper
Taiyo Yuden
TDK
INPUT CAPACITOR SELECTION
A ceramic input capacitor of 4.7
μ
F, 6.3V is sufficient for most
applications. A larger value may be used for improved input
voltage filtering. The input filter capacitor supplies current to
the PFET switch of the LM3370 in the first half of each cycle
and reduces voltage ripple imposed on the input power
source. A ceramic capacitor's low ESR provides the best
noise filtering of the input voltage spikes due to this rapidly
changing current. Select an input filter capacitor with a surge
current rating sufficient for the power-up surge from the input
power source. The power-up surge current is approximately
the capacitor’s value (μF) times the voltage rise rate (V/μs).
The input current ripple can be calculated as:
OUTPUT CAPACITOR SELECTION
DC bias characteristics of ceramic capacitors must be con-
sidered when selecting case sizes like 0805 and 0603. DC
21
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM3370TLX-3008/NOPB | 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 |
| LM3370TLX-3022 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Dual Synchronous Step-Down DC-DC Converter with Dynamic Voltage Scaling Function |
| LM3370TLX-3022/NOPB | 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 |
| LM3370TLX-3206 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Dual Synchronous Step-Down DC-DC Converter with Dynamic Voltage Scaling Function |
| LM3370TLX-3206/NOPB | 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 |
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