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參數(shù)資料
| 型號： | LTC4400-1 |
| 廠商： | Linear Technology Corporation |
| 英文描述： | RF Power Controllers with 450kHz Loop BW and 45dB Dynamic Range |
| 中文描述： | 射頻功率控制器與450kHz環(huán)路帶寬和45dB的動(dòng)態(tài)范圍 |
| 文件頁數(shù)： | 8/16頁 |
| 文件大?。?/td> | 186K |
| 代理商： | LTC4400-1 |
8
LTC4400-1/LTC4400-2
sn4400 4400fas
then apply the ramp signal. The user should wait 12
μ
s after
SHDN has been asserted high before applying the ramp.
The DAC should be settled 2
μ
s after asserting SHDN high.
APPLICATIOU
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General Layout Considerations
The LTC4400-X should be placed near the coupling com-
ponents. The feedback signal line to the RF pin should be
a 50
transmission line with optional termination or a
short line.
External Termination
The LTC4400-X has an internal 250
termination resistor
at the RF pin. If a directional coupler is used, it is recom-
mended that an external 68
termination resistor be
connected between the RF coupling capacitor (33pF), and
ground at the side connected to the directional coupler.
Termination components should be placed adjacent to the
LTC4400-X. An alternative method couples RF from the
power amplifier to the power controller through a 0.4pF
±
0.05pF capacitor and 50
series resistor, completely
eliminating the directional coupler.
Power Ramp Profiles
The external voltage gain associated with the RF channel
can vary significantly between RF power amplifier types.
The LTC4400-X frequency compensation has been
optimized to be stable with several different power ampli-
fiers and manufacturers. This frequency compensation
generally defines the loop dynamics that impact the power/
time response and possibly (slow loops) the power ramp
sidebands. The LTC4400-X operates open loop until an RF
voltage appears at the RF pin, at which time the loop closes
and the output power follows the DAC profile. The RF
power amplifier will require a certain control voltage level
(threshold) before an RF output signal is produced. The
LTC4400-X V
PCA/B
output must quickly rise to this thresh-
old voltage in order to meet the power/time profile. To
reduce this time, the LTC4400-X starts at 450mV. How-
ever, at very low power levels the PCTL input signal is
small, and the V
PCA/B
output may take several microsec-
onds to reach the RF power amplifier threshold voltage. To
reduce this time, it may be necessary to apply a positive
pulse at the start of the ramp to quickly bring the V
PCA/B
output to the threshold voltage. This can generally be
achieved with DAC programming. The magnitude of the
pulse is dependent on the RF amplifier characteristics.
Power ramp sidebands and power/time are also a factor
when ramping to zero power. When the power is ramped
down the loop will eventually open at power levels below
the LTC4400-X detector threshold. The LTC4400-X will
then go open loop and the output voltage at V
PCA/B
will
stop falling. If this voltage is high enough to produce RF
output power, the power/time or power ramp sidebands
may not meet specification. This problem can be avoided
by starting the DAC ramp from 100mV (Figure 1). At the
end of the cycle, the DAC can be ramped down to 0mV.
This applies a negative signal to the LTC4400-X thereby
ensuring that the V
PCA/B
output will ramp to 0V. The
100mV ramp step must be applied <2
μ
s after SHDN is
asserted high to allow the autozero to cancel the step. Slow
DAC rise times will extend this time by the additional RC
time constants which may require that the DAC is enabled
and settled prior to SHDN asserted high.
LTC4400-X Timing Diagram
10
μ
s
28
μ
s
2
μ
s
28
μ
s
543
μ
s
T1
T2 T3
T4
T5
T6
V
START
SHDN
V
PCA/B
PCTL
4400 TA02
T1: LTC4400-X COMES OUT OF SHUTDOWN 12
μ
s PRIOR TO BURST
T2: INTERNAL TIMER COMPLETES AUTOZERO CORRECTION, <10
μ
s
T3: BASEBAND CONTROLLER STARTS RF POWER RAMP UP AT 12
μ
s AFTER
SHDN IS ASSERTED HIGH
T4: BASEBAND CONTROLLER COMPLETES RAMP UP
T5: BASEBAND CONTROLLER STARTS RF POWER RAMP DOWN AT END OF BURST
T6: LTC4400-X RETURNS TO SHUTDOWN MODE BETWEEN BURSTS
T7: BSEL CHANGE PRIOR TO SHDN, 0ns TYPICAL (LTC4400-2 ONLY)
T8: BSEL CHANGE AFTER TO SHDN, 0ns TYPICAL (LTC4400-2 ONLY)
BSEL
T7
T8
(LTC4400-2 ONLY)
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| LTC4400-1ES6#TRMPBF | 功能描述:IC RF POWER CONTROLLER TSOT23-6 RoHS:是 類別:RF/IF 和 RFID >> RF 電源控制器 IC 系列:- 標(biāo)準(zhǔn)包裝:3,000 系列:- RF 型:GSM 頻率:450MHz ~ 2GHz 特點(diǎn):四頻帶 封裝/外殼:8-VFBGA 供應(yīng)商設(shè)備封裝:8-MicroSMD（1.51x1.51） 包裝:帶卷 (TR) 其它名稱:LMV243BLX |
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