Datasheet MAX4473 (Maxim) - 6

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