Minimizing Switching Regulator Residue in Linear Regulator Outputs (Linear Technology) - 4
| Authors | Jim Williams |
| Manufacturer | Linear Technology |
| Description | Application Note 101. Linear regulators are commonly employed to post-regulate switching regulator outputs. Benefits include improved stability, accuracy, transient response and lowered output impedance. Ideally, these performance gains would be accompanied by markedly reduced switching regulator generated ripple and spikes. In practice, all linear regulators encounter some difficulty with ripple and spikes, particularly as frequency rises. This publication explains the causes of linear regulators' dynamic limitations and presents board level techniques for improving ripple and spike rejection. A hardware based ripple/spike simulator is presented, enabling rapid breadboard testing under various conditions. Three appendices review ferrite beads, inductor based filters and probing practice for wideband, sub-millivolt signals. |
| Pages / Page | 12 / 4 — aveforms to Both Paths |
| File Format / Size | PDF / 358 Kb |
| Document Language | English |
aveforms to Both Paths
Text Version of Document
Application Note 101 Ω 30 AN101 F05 LOAD + FB OUTC µF 0.01 OUT BYP GND LT1763-3 REGULATOR UNDER TEST Ω IN SD 100 µF + 22 FB INC Q1 2N3866 5V + Ω1 Ω SPIKE 100 AMPLITUDE L1 Ω Ω 750 750 1k 5V 74AHCO4 SPIKE PATH 15V –15V SPIKE GATING/BUFFER Ω A1 + LT1210 – 750 5V 2k* DC/RIPPLE PATH 2k*
aveforms to Both Paths
5V –5V – C1, 1/2 LT1712 + – C2, 1/2 LT1712 + SPIKE GENERATOR + SYNC. DIFFERENTIATOR/ µF 10 RIPPLE FREQUENCY AND AMPLITUDE CONTROL 1k Ω 50 20pF Ω 50 1.2V –1.2V SYNC. OUTPUT RAMPS OR EQUIVILENT P-P TO 0.1V HP-3310A FUNCTION GENERATOR LOW µF P-P OUTPUT 0.1 BIAS INPUT AMPLITUDE 5V –5V µF REGULATOR DC A2 TYP 3.3V to 3.5V TYP 0.01V 100k* + LT1006 – 0.01 = SEE TEXT 100k* = SEE TEXT IN OUT * = 1% METAL FILM RESISTOR L1 = 4 TURNS #26, 1/4" DIAMETER FB = FERRITE BEAD. FAIR-RITE 2743002122. INDUCTORS OPTIONAL. SEE TEXT = IN4148 C C
Figure 5. Circuit Simulates Switching Regulator Output. DC, Ripple Amplitude, Frequency and Spike Duration/Height are Independantly Settable. Split Path Scheme Sums Wideband Spikes with DC and Ripple, Presenting Linear Regulator with Simulated Switching Regulator Output. Function Generator Sources W
1k SPIKE WIDTH 2.5V LT1460 5V an101f AN101-4
aveforms to Both Paths
5V –5V – C1, 1/2 LT1712 + – C2, 1/2 LT1712 + SPIKE GENERATOR + SYNC. DIFFERENTIATOR/ µF 10 RIPPLE FREQUENCY AND AMPLITUDE CONTROL 1k Ω 50 20pF Ω 50 1.2V –1.2V SYNC. OUTPUT RAMPS OR EQUIVILENT P-P TO 0.1V HP-3310A FUNCTION GENERATOR LOW µF P-P OUTPUT 0.1 BIAS INPUT AMPLITUDE 5V –5V µF REGULATOR DC A2 TYP 3.3V to 3.5V TYP 0.01V 100k* + LT1006 – 0.01 = SEE TEXT 100k* = SEE TEXT IN OUT * = 1% METAL FILM RESISTOR L1 = 4 TURNS #26, 1/4" DIAMETER FB = FERRITE BEAD. FAIR-RITE 2743002122. INDUCTORS OPTIONAL. SEE TEXT = IN4148 C C
Figure 5. Circuit Simulates Switching Regulator Output. DC, Ripple Amplitude, Frequency and Spike Duration/Height are Independantly Settable. Split Path Scheme Sums Wideband Spikes with DC and Ripple, Presenting Linear Regulator with Simulated Switching Regulator Output. Function Generator Sources W
1k SPIKE WIDTH 2.5V LT1460 5V an101f AN101-4
