MAX4473 Просмотр технического описания (PDF) - Maxim Integrated
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MAX4473 Datasheet PDF : 9 Pages
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Low-Cost, Low-Voltage, PA Power Control
Amplifier for GSM Applications
Applications Information
Gain Resistor Selection
(RG1, RG2, RG3)
For proper operation, do not make the value of external
gain resistors RG1 and RG2 larger than twice the value
of RG3. In most practical applications, choose RG1
smaller than RG3 to limit the voltage drop over RG1
and RSENSE. A large voltage drop over RSENSE sub-
stantially reduces the voltage applied to the PA, thus
reducing PA output power. Set RG2 equal to RG1 to
compensate for the input bias currents of A3.
Recommended values for RG3 are between 1kΩ and
10kΩ.
Sense Resistor Selection (RSENSE)
Choose RSENSE based on the following criteria:
• Voltage Loss: A high RSENSE value causes the
power-source voltage to degrade through IR loss.
For minimal voltage loss, use low RSENSE values.
• Accuracy: A high RSENSE value allows lower cur-
rents to be measured more accurately because input
offset voltages become less significant when the
sense voltage is larger. For best performance, select
RSENSE to provide approximately 100mV of sense
voltage for the full-scale current in each application.
• Efficiency and Power Dissipation: At high current
levels, the I2R losses in RSENSE are significant. Take
this into consideration when choosing the resistor
value and its power dissipation (wattage) rating.
Also, the sense resistor’s value may drift if it is
allowed to heat up excessively.
_________________________Test Circuit
VCC
0.1μF
RSENSE
RG1
100Ω
RG2
1kΩ
0.1%
1kΩ
1%
1%
VCC
SR1
SR2
PC
SHDN
GND
MAX4473
SR3
RG3
2.5kΩ
1%
OUT
RL
10kΩ
CL
300pF
2N3904
RE
750Ω
TOP VIEW
Pin Configuration
SR1 1
SR2 2
SHDN 3
PC 4
MAX4473
8 VCC
7 OUT
6 SR3
5 GND
μMAX/SO
Chip Information
TRANSISTOR COUNT: 348
6 _______________________________________________________________________________________
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