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參數(shù)資料
| 型號： | LM3203TLX |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | Step-Down DC-DC Converter with Bypass Mode for CDMA / WCDMA RF Power Amplifiers |
| 中文描述： | SWITCHING REGULATOR, 2200 kHz SWITCHING FREQ-MAX, BGA10 |
| 封裝： | LEAD FREE, THIN MICRO BUMP, 10 PIN |
| 文件頁數(shù)： | 11/15頁 |
| 文件大?。?/td> | 1360K |
| 代理商： | LM3203TLX |
Operation Description
(Continued)
Circuit Operation
Referring to
Figure 1
, the LM3203 operates as follows. Dur-
ing the first part of each switching cycle, the control block in
the LM3203 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) syn-
chronous rectifier on. In response, the inductor’s magnetic
field collapses, 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 capaci-
tor stores charge when the inductor current is going high,
and releases it when inductor current is going low, smooth-
ing 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 LM3203 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. It remains
in bypass mode until BYP pin goes low.
It is recommended to connect BYPOUT pin directly to the
output capacitor with a separate trace and not to the FB pin.
Connect the BYPOUT pin to the V
DD
pin when Bypass mode
is not required.
If V
CON
is less than approx. 0.15V, the Bypass FET is turned
off.
Operating Mode Selection Control
The LM3203 is designed for digital control of the operating
modes using the BYP pin. Setting the BYP pin high (
>
1.2V)
places the device in Bypass mode. Setting BYP pin low
(
<
0.4V) forces operation in PWM mode.
Bypass and PWM operation overlap during the transition
between the two modes. This transition time is approxi-
mately 31μs when changing from PWM to Bypass mode,
and 15μs when changing from Bypass to PWM mode. This
helps prevent under or overshoots during the transition pe-
riod between PWM and Bypass modes.
20141636
FIGURE 1. Typical Operating System Circuit where baseband controls the output voltage using a DAC
L
www.national.com
11
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM3203TLX/J7002328 | 制造商:Rochester Electronics LLC 功能描述: 制造商:Texas Instruments 功能描述: |
| LM3203TLX/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 |
| LM3204 | 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 |
| 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 |
| LM3204TL/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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