參數(shù)資料
型號(hào)： LM3204
廠商： National Semiconductor Corporation
元件分類： DC/DC變換器
英文描述： Miniature, Adjustable, Step-Down DC-DC Converter with Bypass Mode for RF Power Amplifiers
中文描述： 微型，可調(diào)，降壓的DC - DC轉(zhuǎn)換器旁路模式射頻功率放大器
文件頁(yè)數(shù)： 12/16頁(yè)
文件大?。?/td> 874K
代理商： LM3204
Operation Description
(Continued)
Circuit Operation
Referring to
Figure 1
, the LM3204 operates as follows. Dur-
ing the first part of each switching cycle, the control block in
the LM3204 turns on the internal PFET (P-channel MOS-
FET) 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
around (V
- V
) / L, by storing energy in a magnetic field.
During the second part of each cycle, the controller turns the
PFET switch off, blocking current flow from the input, and
then turns the NFET (N-channel MOSFET) synchronous
rectifier on. In response, the inductor’s magnetic field col-
lapses, generating a voltage that forces current from ground
through the synchronous rectifier to the output filter capacitor
and load. As the stored energy is transferred back into the
circuit and depleted, the inductor current ramps down with a
slope around V
OUT
/ L. The output filter capacitor stores
charge when the inductor current is going high, and releases
it when inductor current is going low, smoothing the voltage
across the load.
The output voltage is regulated by modulating the PFET
switch on time to control the average current sent to the load.
The effect is identical to sending a duty-cycle modulated
rectangular wave formed by the switch and synchronous
rectifier at SW to a low-pass filter formed by the inductor and
output filter capacitor. The output voltage is equal to the
average voltage at the SW pin.
PWM Mode
While in PWM (Pulse Width Modulation) mode, the output
voltage is regulated by switching at a constant frequency
and then modulating the energy per cycle to control power to
the load. Energy per cycle is set by modulating the PFET
switch on-time pulse width to control the peak inductor cur-
rent. This is done by comparing the PFET drain current to a
slope-compensated reference current generated by the error
amplifier. At the beginning of each cycle, the clock turns on
the PFET switch, causing the inductor current to ramp up.
When the current sense signal ramps past the error amplifier
signal, the PWM comparator turns off the PFET switch and
turns on the NFET synchronous rectifier, ending the first part
of the cycle. If an increase in load pulls the output down, the
error amplifier output increases, which allows the inductor
current to ramp higher before the comparator turns off the
PFET. This increases the average current sent to the output
and adjusts for the increase in the load. The minimum on-
time of PFET in PWM mode is 50ns (typ.).
Bypass Mode
The LM3204 contains an internal PFET switch for bypassing
the PWM DC-DC converter during Bypass mode. In Bypass
mode, this PFET is turned on to power the PA directly from
the battery for maximum RF output power. Bypass mode is
more efficient than operating in PWM mode at 100% duty
cycle because the resistance of the bypass PFET is less
than the series resistance of the PWM PFET and inductor.
This translates into higher voltage available on the output in
Bypass mode, for a given battery voltage. The part can be
placed in bypass mode by sending BYP pin high. This is
called Forced Bypass Mode and it remains in bypass mode
until BYP pin goes low.
Alternatively the part can go into Bypass mode automatically.
This is calledAuto-bypass mode orAutomatic Bypass mode.
The bypass switch turns on when the difference between the
input voltage and programmed output voltage is less than
250mV (typ.) for more than the bypass delay time of 15μs
(typ.). The bypass switch turns off when the input voltage is
higher than the programmed output voltage by 450mV (typ.)
for longer than the bypass delay time. The bypass delay time
is provided to prevent false triggering into Automatic Bypass
mode by either spikes or dips in V
. This method is very
system resource friendly in that the Bypass PFET is turned
on automatically when the input voltage gets close to the
output voltage, typical scenario of a discharging battery. It is
also turned off automatically when the input voltage rises,
typical scenario of a charger connected. Another scenario
could be changes made to V
voltage causing Bypass
PFET to turn on and off automatically. It is recommended to
connect BYPOUT pin directly to the output capacitor with a
separate trace and not to the FB pin.
If the V
CON
is less than approximately 0.15V, the Bypass
FET is turned off.
20138936
FIGURE 1. Typical Operating System Circuit
L
www.national.com
12
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相關(guān)代理商/技術(shù)參數(shù)
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LM3204TL 制造商:Rochester Electronics LLC 功能描述: 制造商:Texas Instruments 功能描述:CONVERTER BUCK 0.5A ADJ POWERWISE
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LM3204TLEV 功能描述:電源管理IC開發(fā)工具 LM3204 EVAL BOARD RoHS:否 制造商:Maxim Integrated 產(chǎn)品:Evaluation Kits 類型:Battery Management 工具用于評(píng)估:MAX17710GB 輸入電壓: 輸出電壓:1.8 V
LM3204TLX 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Miniature, Adjustable, Step-Down DC-DC Converter with Bypass Mode for RF Power Amplifiers
LM3204TLX/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(fēng)格: 封裝 / 箱體:CPAK
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