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PAM3112FUK120 Datasheet(PDF) 7 Page - Power Analog Micoelectronics |
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PAM3112FUK120 Datasheet(HTML) 7 Page - Power Analog Micoelectronics |
7 / 16 page Application Information 7 PAM3112 300mA CMOS Linear Regulator Capacitor Selection and Regulator Stability Load Transient Considerations Shutdown Input Operation Internal P-Channel Pass Transistor Input-Output ( Dropout ) Voltage Current Limit and Short Circuit Protection Thermal considerations Similar to any low dropout regulator, the external capacitors used with the PAM3112 must be carefully selected for regulator stability and performance. A capacitor C of more than 1 F can be used at the PAM3112 input pin, while there is no upper limit for the capacitance of C . Please note that the distance between C and the input pin of the PAM3112 should not exceed 0.5 inch. Ceramic capacitors a re suitable f or the PAM3112. Capacitors with larger values and lower ESR (equivalent series resistance) provide better PSRR and line-transient response. The PAM3112 is designed specifically to work with low ESR ceramic output capacitors in order to save space and improve performance. Using an output ceramic capacitor whose value is > A 10nF bypass capacitor connected to BYP pin is suggested for suppressing output noise. The capacitor, in series connection with an internal 200k resistor, forms a low-pass filter for noise reduction. Increasing the capacitance will slightly decrease the output noise, but increase the start- up time. Curve of the PAM3112 load-transient response shows two components of the output response, a DC shift from the output impedance due to the load current change and transient response. The DC shift is quite small due to excellent load regulation of the PAM3112. The transient spike, resulting from a step change in the load current from 1mA to 300mA, is 20mV. The ESR of the output capacitor is critical to the transient spike. A larger capacitance along with smaller ESR results in a is smaller spike. The PAM3112 is shut down by pulling the EN input low and turned on by tying the EN input to VIN or leaving the EN input floating. The PAM3112 features a 0.75 device as a pass transistor. The P-MOS pass transistor enables the PAM3112 to consume only 65 A of ground current during low dropout, light-load, or heavy-load operation. These features increase the battery operation life time. A regulator's minimum input-output voltage difference (or dropout voltage) determines the lowest usable supply voltage. The PAM3112 has a typical 300mV dropout voltage. In battery- powered systems, this will determine the useful end-of-life battery voltage. The PAM3112 features a current limit, which monitors and controls the gate voltage of the pass transistor. The output current can be limited to 400mA by regulating the gate voltage. The PAM3112 also has a built-in short circuit current limit. Thermal protection limits power dissipation in the PAM3112. When the junction temperature exceeds 150°C, the OTP (Over Temperature Protection) starts the thermal shutdown and turns the pass transistor off. The pass transistor resumes operation after the junction temperature drops below 120°C. For c ontinuous operation, the junction temperature should be maintained below 125°C. The power dissipation is defined as: P = (V -V )*I +V *I The maximum power dissipation depends on the thermal resistance of IC package, PCB layout, the rate of surrounding airflow and temperature difference between junction and ambient. The maximum power dissipation can be calculated by the following formula: IN IN IN D IN OUT O IN GND μ 2.2μF with ESR>5mΩ ensures stability. Ω Ω P-Channel MOSFET μ P = (T -T )/θ D(MAX) J(MAX) A JA 7 on page 6 10/2008 Rev 1.3 , Power Analog Microelectronics Inc www.poweranalog.com |
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