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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)： | 13/16頁(yè) |
| 文件大?。?/td> | 874K |
| 代理商： | LM3204 |
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Operating Mode Selection Control
The BYP digital input pin is used to select between PWM/
Auto-bypass and Bypass operating mode. Setting BYP pin
high (
>
1.2V) places the device in Forced Bypass mode.
Setting BYP pin low (
<
0.4V) or leaving it floating places the
device in PWM/Auto-bypass 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.
Shutdown Mode
Setting the EN digital pin low (
<
0.4V) places the LM3204 in
a 0.1μA (typ.) Shutdown mode. During shutdown, the PFET
switch, NFET synchronous rectifier, reference voltage
source, control and bias circuitry of the LM3204 are turned
off. Setting EN high (
>
1.2V) enables normal operation.
EN should be set low to turn off the LM3204 during power-up
and under voltage conditions when the power supply is less
than the 2.7V minimum operating voltage. The LM3204 is
designed for compact portable applications, such as mobile
phones. In such applications, the system controller deter-
mines power supply sequencing and requirements for small
package size outweigh the benefit of including UVLO (Under
Voltage Lock-Out) circuitry.
Dynamically Adjustable Output
Voltage
The LM3204 features dynamically adjustable output voltage
to eliminate the need for external feedback resistors. The
output can be set from 0.8V to 3.6V by changing the voltage
on the analog V
pin. This feature is useful in PA applica-
tions where peak power is needed only when the handset is
far away from the base station or when data is being trans-
mitted. In other instances, the transmitting power can be
reduced. Hence the supply voltage to the PA can be re-
duced, promoting longer battery life. See
Setting the Output
Voltage
in the
Application Information
section for further
details.
Over Voltage Protection
The LM3204 has an over voltage comparator that prevents
the output voltage from rising too high, when the device is
left in PWM mode under light-load conditions, during output
voltage steps, or during startup. When the output voltage
rises to 330mV over its target, the OVP comparator inhibits
PWM operation to skip pulses until the output voltage returns
to the target. During the over voltage protection mode, both
the PWM PFET and the NFET synchronous rectifier are off.
When the part comes out of the over voltage protection
mode, the NFET synchronous rectifier remains off for ap-
proximately 3.5μs to avoid inductor current going negative.
Internal Synchronous Rectification
While in PWM mode, the LM3204 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.
With medium and heavy loads, the internal NFET synchro-
nous rectifier is turned on during the inductor current down
slope in the second part of each cycle. The synchronous
rectifier is turned off prior to the next cycle. There is no zero
cross detect, which means that the NFET can conduct cur-
rent in both directions and inductor current is always con-
tinuous. The advantage of this method is that the part re-
mains in PWM mode at light loads or no load conditions. The
NFET has a current limit. The NFET is designed to conduct
through its intrinsic body diode during transient intervals
before it turns on, eliminating the need for an external diode.
Current Limiting
A current limit feature allows the LM3204 to protect itself and
external components during overload conditions. In PWM
mode, a 940mA (max.) cycle-by-cycle current limit is nor-
mally used. If an excessive load pulls the output voltage
down to below approximately 0.375V, indicating a possible
short to ground, then the device switches to a timed current
limit mode. In timed current limit mode, the internal PFET
switch is turned off after the current comparator trips, and the
beginning of the next cycle is inhibited for 3.5μs to force the
instantaneous inductor current to ramp down to a safe value.
After the 3.5μs interval, the internal PFET is turned on again.
This cycle is repeated until the load is reduced and the
output voltage exceeds approximately 0.375V. Therefore,
the device may not startup if an excessive load is connected
to the output when the device is enabled. The synchronous
rectifier is off in the timed current limit mode. Timed current
limit prevents the loss of current control seen in some prod-
ucts when the output voltage is pulled low in serious over-
load conditions.
A current limit is also provided for the NFET. This is approxi-
mately 500mA. Both the NFET and the PFET are turned off
in negative current limit until the PFET is turned on again at
the beginning of the next cycle. The negative current limit
inhibits buildup of excessive negative inductor current.
In the Bypass mode, the bypass current limit is 1000mA
(typ.). The output voltage drops when the bypass current
limit kicks in.
Thermal Overload Protection
The LM3204 has a thermal overload protection function to
protect the device from short-term misuse and overload
conditions. When the junction temperature exceeds around
150C, the device inhibits operation. Both the PFET and the
NFET are turned off in PWM mode, and the Bypass PFET is
turned off in Bypass mode. When the temperature drops
below 130C, normal operation resumes. Prolonged opera-
tion in thermal overload conditions may damage the device.
Application Information
SETTING THE OUTPUT VOLTAGE
The LM3204 features a pin-controlled variable output volt-
age to eliminate the need for external feedback resistors. It
can be programmed for an output voltage from 0.8V to 3.6V
by setting the voltage on the V
CON
pin, as in the following
formula:
V
OUT
= 3 x V
CON
When V
is between 0.267V and 1.20V, the output volt-
age will follow proportionally by 3 times of V
CON
.
If V
is over 1.20V (V
= 3.6V), sub-harmonic oscilla-
tion may occur because of insufficient slope compensation.
L
www.national.com
13
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| 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(kāi)關(guān)控制器 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開(kāi)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 |
| LM3204TLEV | 功能描述:電源管理IC開(kāi)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(kāi)關(guān)控制器 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開(kāi)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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