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參數(shù)資料
| 型號： | LM3102TL-1 |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | SWITCHING REGULATOR, 1000 kHz SWITCHING FREQ-MAX, PBGA28 |
| 封裝： | USMD-28 |
| 文件頁數(shù)： | 3/20頁 |
| 文件大?。?/td> | 623K |
| 代理商： | LM3102TL-1 |
Functional Description
The LM3102 Step Down Switching Regulator features all re-
quired functions to implement a cost effective, efficient buck
power converter capable of supplying 2.5A to a load. It con-
tains Dual N-Channel main and synchronous MOSFETs. The
Constant ON-Time (COT) regulation scheme requires no loop
compensation, results in fast load transient response and
simple circuit implementation. The regulator can function
properly even with an all ceramic output capacitor network,
and does not rely on the output capacitor’s ESR for stability.
The operating frequency remains constant with line variations
due to the inverse relationship between the input voltage and
the on-time. The valley current limit detection circuit, with the
limit set internally at 2.7A, inhibits the main MOSFET until the
inductor current level subsides.
The LM3102 can be applied in numerous applications and
can operate efficiently for inputs as high as 42V. Protection
features include output over-voltage protection, thermal shut-
down, V
CC under-voltage lock-out, gate drive under-voltage
lock-out. The LM3102 is available in the thermally enhanced
eTSSOP-20 package.
COT Control Circuit Overview
COT control is based on a comparator and a one-shot on-
timer, with the output voltage feedback (feeding to the FB pin)
compared with an internal reference of 0.8V. If the voltage of
the FB pin is below the reference, the main MOSFET is turned
on for a fixed on-time determined by a programming resistor
R
ON and the input voltage VIN, upon which the on-time varies
inversely. Following the on-time, the main MOSFET remains
off for a minimum of 260 ns. Then, if the voltage of the FB pin
is below the reference, the main MOSFET is turned on again
for another on-time period. The switching will continue to
achieve regulation.
The regulator will operate in the discontinuous conduction
mode (DCM) at a light load, and the continuous conduction
mode (CCM) with a heavy load. In the DCM, the current
through the inductor starts at zero and ramps up to a peak
during the on-time, and then ramps back to zero before the
end of the off-time. It remains zero and the load current is
supplied entirely by the output capacitor. The next on-time
period starts when the voltage at the FB pin falls below the
internal reference. The operating frequency in the DCM is
lower and varies larger with the load current as compared with
the CCM. Conversion efficiency is maintained since conduc-
tion loss and switching loss are reduced with the reduction in
the load and the switching frequency respectively. The oper-
ating frequency in the DCM can be calculated approximately
as follows:
(1)
In the continuous conduction mode (CCM), the current flows
through the inductor in the entire switching cycle, and never
reaches zero during the off-time. The operating frequency re-
mains relatively constant with load and line variations. The
CCM operating frequency can be calculated approximately as
follows:
(2)
The output voltage is set by two external resistors R
FB1 and
R
FB2. The regulated output voltage is
V
OUT = 0.8V x (RFB1 + RFB2)/RFB2
(3)
Startup Regulator (V
CC)
A startup regulator is integrated within the LM3102. The input
pin VIN can be connected directly to a line voltage up to 42V.
The V
CC output regulates at 6V, and is current limited to 65
mA. Upon power up, the regulator sources current into an ex-
ternal capacitor C
VCC, which is connected to the VCC pin. For
stability, C
VCC must be at least 680 nF. When the voltage on
the VCC pin is higher than the under-voltage lock-out (UVLO)
threshold of 3.75V, the main MOSFET is enabled and the SS
pin is released to allow the soft-start capacitor C
SS to charge.
The minimum input voltage is determined by the dropout volt-
age of the regulator and the V
CC UVLO falling threshold
(
3.7V). If V
IN is less than 4.0V, the regulator shuts off and
V
CC goes to zero.
Regulation Comparator
The feedback voltage at the FB pin is compared to a 0.8V
internal reference. In normal operation (the output voltage is
regulated), an on-time period is initiated when the voltage at
the FB pin falls below 0.8V. The main MOSFET stays on for
the on-time, causing the output voltage and consequently the
voltage of the FB pin to rise above 0.8V. After the on-time
period, the main MOSFET stays off until the voltage of the FB
pin falls below 0.8V again. Bias current at the FB pin is nom-
inally 5 nA.
Zero Coil Current Detect
The current of the synchronous MOSFET is monitored by a
zero coil current detection circuit which inhibits the syn-
chronous MOSFET when its current reaches zero until the
next on-time. This circuit enables the DCM operation, which
improves the efficiency at a light load.
Over-Voltage Comparator
The voltage at the FB pin is compared to a 0.92V internal
reference. If it rises above 0.92V, the on-time is immediately
terminated. This condition is known as over-voltage protec-
tion (OVP). It can occur if the input voltage or the output load
changes suddenly. Once the OVP is activated, the main
MOSFET remains off until the voltage at the FB pin falls below
0.92V. The synchronous MOSFET will stay on to discharge
the inductor until the inductor current reduces to zero, and
then switch off.
ON-Time Timer, Shutdown
The on-time of the LM3102 main MOSFET is determined by
the resistor R
ON and the input voltage VIN. It is calculated as
follows:
(4)
The inverse relationship of t
on and VIN gives a nearly constant
frequency as V
IN is varied. RON should be selected such that
the on-time at maximum V
IN is greater than 150 ns. The on-
timer has a limiter to ensure a minimum of 150 ns for t
on. This
limits the maximum operating frequency, which is governed
by the following equation:
11
www.national.com
LM3102
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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| LM3102TL-1/NOPB | 功能描述:直流/直流開關轉換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風格:SMD/SMT |
| LM3102TLX-1/NOPB | 功能描述:直流/直流開關轉換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風格:SMD/SMT |
| LM3103 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:SIMPLE SWITCHER㈢ Synchronous 1MHz 0.75A Step-Down Voltage Regulator |
| LM3103EVAL | 功能描述:電源管理IC開發(fā)工具 LM3103 EVAL BOARD RoHS:否 制造商:Maxim Integrated 產(chǎn)品:Evaluation Kits 類型:Battery Management 工具用于評估:MAX17710GB 輸入電壓: 輸出電壓:1.8 V |
| LM3103EVAL/NOPB | 功能描述:電源管理IC開發(fā)工具 LM3103 EVAL BRD RoHS:否 制造商:Maxim Integrated 產(chǎn)品:Evaluation Kits 類型:Battery Management 工具用于評估:MAX17710GB 輸入電壓: 輸出電壓:1.8 V |
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