EMT 212 ANALOG ELECTRONICS Professor Robert T Kennedy

Prof. R T Kennedy

EXTERNAL CAPACITORS Prof. R T Kennedy PART OF 50Hz SMOOTHING rf decoupling AIDS LOAD TRANSIENT RESPONSE

ROLE OF OUTPUT CAPACITOR C 3 C 3 DETERMINES 3 CHARACTERISTICS START UP DELAY START UP DELAY LOAD TRANSIENT RESPONSE LOAD TRANSIENT RESPONSE LOOP STABILITY LOOP STABILITY Prof. R T Kennedy

OUTPUT COMPENSATION C 3 NPN PASS unconditionally stable NPN PASS unconditionally stable NO NEED FOR C 3 NO NEED FOR C 3 LDO PNP NEED AT LEAST C 3 LDO PNP NEED AT LEAST C 3 QUASI LDO (NPN + PNP DRIVER) QUASI LDO (NPN + PNP DRIVER) SMALLER C 3 Prof. R T Kennedy

START UP TRANSIENT RESPONSE Prof. R T Kennedy

IDEAL LOOP RESPONSE UNCONDITIONAL STABILITY Prof. R T Kennedy

NPN OUTPUT STRUCTURE Prof. R T Kennedy P 1 DOMINANT POLE ~ 100Hz -20dB/decade -40dB/dec LARGE PHASE MARGIN

PNP OUTPUT STRUCTURE Prof. R T Kennedy internal pole NO PHASE MARGIN

PNP OUTPUT STRUCTURE Prof. R T Kennedy ZERO DUE TO CAPACITOR esr PHASE MARGIN

CAPACITOR SELECTION NOT JUST C ! Esr NOT JUST C ! Esr TYPE – DIELECTRIC TYPE – DIELECTRIC COST & AVAILABILITY COST & AVAILABILITY TEMPERATURE CONSTRAINTS TEMPERATURE CONSTRAINTS START DATA SHEET COMPENSATION C 3 START DATA SHEET COMPENSATION C 3 Prof. R T Kennedy

CAPACITOR PARAMETERS & RATINGS PARAMETERS RATINGS CAPACITANCE ESR ESL VOLTAGE CURRENT TEMPERATURE

TYPICAL LDO esr RANGE Prof. R T Kennedy

TEMPERATURE LOW TEMPERATURES LOOP GAIN INCREASES LOOP GAIN INCREASES CAPACITOR esr INCREASES CAPACITOR esr INCREASES CAPACITANCE DECREASES CAPACITANCE DECREASES POLES SHIFT POLES SHIFT GAIN INCREASES GAIN INCREASES PHASE MARGIN DECREASES PHASE MARGIN DECREASES UNSTABLE -- OSCILLATIONS UNSTABLE -- OSCILLATIONS Prof. R T Kennedy

CAPACITOR TYPES: DIELECTRIC FILM POLYESTER POLYCARBONATE POLYPROPYLENE POLYSTYRENE PAPER CERAMIC ELECTROLYTIC SINGLE LAYER MULTI-LAYER ALUMINIUM TANTALUM

ALUMINIUM DIELECTRIC Prof. R T Kennedy

CAPACITOR PARASITICS IDEAL REAL C ESL ESR C R dc RacRac RdRd CdCd CIDEAL C ESLLEADS ELECTRODES ESRLEADS ELECTRODES TERMINATIONS R dc DIELECTRIC LEAKAGE ESL ESR C RdcRdc AC dielectric loss dielectric absorption properties ideal linear function of temperature significant when f > 200 kHz losses, heating, temp.

EXTERNAL CAPACITORS Prof. R T Kennedy PART OF 50Hz SMOOTHING rf decoupling AIDS LOAD TRANSIENT RESPONSE