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参数资料
| 型号： | LM3370TLX-2613/NOPB |
| 厂商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分类： | 稳压器 |
| 英文描述： | 1.4 A DUAL SWITCHING CONTROLLER, 2400 kHz SWITCHING FREQ-MAX, PBGA20 |
| 封装： | 3 X 2 MM, 0.60 MM HEIGHT, 0.50 MM PITCH, , MO-211DG, MICRO, SMD-20 |
| 文件页数： | 6/26页 |
| 文件大小： | 5436K |
| 代理商： | LM3370TLX-2613/NOPB |
Operation Description
DEVICE INFORMATION
The LM3370, a dual high efficiency step-down DC-DC con-
verter, delivers regulated voltages from input rails between
2.7V to 5.5V. Using voltage mode architecture with syn-
chronous rectification, the LM3370 has the ability to deliver
up to 600 mA per channel. The performance is optimized for
systems where efficiency and space are critical.
There are three modes of operation depending on the current
required: PWM, PFM, and shutdown. PWM mode handles
loads of approximately 70 mA or higher with 90% efficiency
or better. Lighter loads cause the device to automatically
switch into PFM mode to maintain high efficiency with low
supply current (I
Q = 20 A typ.) per channel.
The LM3370 can operate up to a 100% duty cycle (PFET
switch always on) for low drop out control of the output volt-
age. In this way the output voltage will be controlled down to
the lowest possible input voltage.
Additional features include soft-start, under-voltage lock-out,
current overload protection, and thermal overload protection.
CIRCUIT OPERATION
During the first portion of each switching cycle, the control
block in the LM3370 turns on the internal PFET switch. This
allows current to flow from the input through the inductor to
the output filter capacitor and load. The inductor limits the
current to a ramp with a slope of
by storing energy in a magnetic field. During the second por-
tion of each cycle, the controller turns the PFET switch off,
blocking current flow from the input, and then turns the NFET
synchronous rectifier on. The inductor draws current from
ground through the NFET to the output filter capacitor and
load, which ramps the inductor current down with a slope of
The output filter stores charge when the inductor current is
high, and releases it when low, smoothing the voltage across
the load.
PWM OPERATION
During PWM operation the converter operates as a voltage-
mode controller with input voltage feed forward. This allows
the converter to achieve excellent load and line regulation.
The DC gain of the power stage is proportional to the input
voltage. To eliminate this dependence, feed forward inversely
proportional to the input voltage is introduced.
INTERNAL SYNCHRONOUS RECTIFICATION
While in PWM mode, the LM3370 uses an internal NFET as
a synchronous rectifier to reduce rectifier forward voltage
drop and associated power loss. Synchronous rectification
provides a significant improvement in efficiency whenever the
output voltage is relatively low compared to the voltage drop
across an ordinary rectifier diode.
CURRENT LIMITING
A current limit feature allows the LM3370 to protect itself and
external components during overload conditions. PWM mode
implements cycle-by-cycle current limiting using an internal
comparator that trips at 1200 mA (typ.). If the outputs are
shorted to ground the device enters a timed current limit mode
where the NFET is turned on for a longer duration until the
inductor current falls below a low threshold, ensuring inductor
has more time to decay, thereby preventing runaway.
PFM OPERATION
At very light loads, the converter enters PFM mode and op-
erates with reduced switching frequency and supply current
to maintain high efficiency.
The part will automatically transition into PFM mode when ei-
ther of two conditions are true, for a duration of 32 or more
clock cycles:
1.
The NFET current reaches zero.
2.
The peak PFET switch current drops below the I
MODE
level .
Supply current during this PFM mode is less than 20 A per
channel, which allows the part to achieve high efficiency un-
der extremely light load conditions. When the output drops
below the ‘low’ PFM threshold, the cycle repeats to restore
the output voltage to
1.2% above the nominal PWM output
voltage.
If the load current should increase during PFM mode (see
Figure 2) causing the output voltage to fall below the ‘low2’
PFM threshold, the part will automatically transition into fixed-
frequency PWM mode.
During PFM operation, the converter positions the output volt-
age slightly higher than the nominal output voltage during
PWM operation, allowing additional headroom for voltage
drop during a load transient from light to heavy load. The PFM
comparators sense the output voltage via the feedback pin
and control the switching of the output FETs such that the
output voltage ramps between 0.8% and 1.6% (typical) above
the nominal PWM output voltage. If the output voltage is be-
low the ‘high’ PFM comparator threshold, the PFET power
switch is turned on. It remains on until the output voltage ex-
ceeds the ‘high’ PFM threshold or the peak current exceeds
the I
PFM level set for PFM mode. The typical peak current in
PFM mode is:
I
PFM = 115 mA + VIN/57
Once the PFET power switch is turned off, the NFET power
switch is turned on until the inductor current ramps to zero.
When the NFET zero-current condition is detected, the NFET
power switch is turned off. If the output voltage is below the
‘high’ PFM comparator threshold (see Figure 2), the PFET
switch is again turned on and the cycle is repeated until the
output reaches the desired level. Once the output reaches the
‘high’ PFM threshold, the NFET switch is turned on briefly to
ramp the inductor current to zero and then both output switch-
es are turned off and the part enters an extremely low power
mode.
www.national.com
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LM3370
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| LM3370TL-2613/NOPB | 1.4 A DUAL SWITCHING CONTROLLER, 2400 kHz SWITCHING FREQ-MAX, PBGA20 |
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相关代理商/技术参数 |
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| LM3370TLX-3006 | 制造商:NSC 制造商全称:National Semiconductor 功能描述:Dual Synchronous Step-Down DC-DC Converter with Dynamic Voltage Scaling Function |
| LM3370TLX-3006/NOPB | 功能描述:DC/DC 开关控制器 RoHS:否 制造商:Texas Instruments 输入电压:6 V to 100 V 开关频率: 输出电压:1.215 V to 80 V 输出电流:3.5 A 输出端数量:1 最大工作温度:+ 125 C 安装风格: 封装 / 箱体:CPAK |
| LM3370TLX-3008 | 制造商:NSC 制造商全称:National Semiconductor 功能描述:Dual Synchronous Step-Down DC-DC Converter with Dynamic Voltage Scaling Function |
| LM3370TLX-3008/NOPB | 功能描述:DC/DC 开关控制器 RoHS:否 制造商:Texas Instruments 输入电压:6 V to 100 V 开关频率: 输出电压:1.215 V to 80 V 输出电流:3.5 A 输出端数量:1 最大工作温度:+ 125 C 安装风格: 封装 / 箱体:CPAK |
| LM3370TLX-3022 | 制造商:NSC 制造商全称:National Semiconductor 功能描述:Dual Synchronous Step-Down DC-DC Converter with Dynamic Voltage Scaling Function |
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