Datasheet LT3020, LT3020-1.2, LT3020-1.5, LT3020-1.8 (Analog Devices) - 10
| Fabricante | Analog Devices |
| Descripción | 100mA, Low Voltage, Very Low Dropout Linear Regulator |
| Páginas / Página | 16 / 10 — APPLICATIO S I FOR ATIO. Output Capacitance and Transient Response. … |
| Formato / tamaño de archivo | PDF / 221 Kb |
| Idioma del documento | Inglés |
APPLICATIO S I FOR ATIO. Output Capacitance and Transient Response. Figure 2. Ceramic Capacitor DC Bias Characteristics
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- LT3020EDD#PBF LT3020EDD#PBF LT3020EDD#TRPBF LT3020EDD#TRPBF LT3020EDD-1.2#PBF LT3020EDD-1.2#PBF LT3020EDD-1.2#TRPBF LT3020EDD-1.2#TRPBF LT3020EDD-1.5#PBF LT3020EDD-1.5#PBF LT3020EDD-1.5#TRPBF LT3020EDD-1.5#TRPBF LT3020EDD-1.8#PBF LT3020EDD-1.8#PBF LT3020EDD-1.8#TRPBF LT3020EDD-1.8#TRPBF LT3020EMS8#PBF LT3020EMS8#PBF LT3020EMS8#TRPBF LT3020EMS8#TRPBF LT3020EMS8-1.2#PBF LT3020EMS8-1.2#PBF LT3020EMS8-1.2#TRPBF LT3020EMS8-1.2#TRPBF LT3020EMS8-1.5#PBF LT3020EMS8-1.5#PBF LT3020EMS8-1.5#TRPBF LT3020EMS8-1.5#TRPBF LT3020EMS8-1.8#PBF LT3020EMS8-1.8#PBF LT3020EMS8-1.8#TRPBF LT3020EMS8-1.8#TRPBF LT3020IDD#PBF LT3020IDD#PBF LT3020IDD#TRPBF LT3020IDD#TRPBF LT3020IDD-1.2#PBF LT3020IDD-1.2#PBF LT3020IDD-1.2#TRPBF LT3020IDD-1.2#TRPBF LT3020IDD-1.5#PBF LT3020IDD-1.5#PBF LT3020IDD-1.5#TRPBF LT3020IDD-1.5#TRPBF LT3020IDD-1.8#PBF LT3020IDD-1.8#PBF LT3020IDD-1.8#TRPBF LT3020IDD-1.8#TRPBF LT3020IMS8#PBF LT3020IMS8#PBF LT3020IMS8#TRPBF LT3020IMS8#TRPBF LT3020IMS8-1.2#PBF LT3020IMS8-1.2#PBF LT3020IMS8-1.2#TRPBF LT3020IMS8-1.2#TRPBF LT3020IMS8-1.5#PBF LT3020IMS8-1.5#PBF LT3020IMS8-1.5#TRPBF LT3020IMS8-1.5#TRPBF LT3020IMS8-1.8#PBF LT3020IMS8-1.8#PBF LT3020IMS8-1.8#TRPBF LT3020IMS8-1.8#TRPBF
Versión de texto del documento
LT3020/LT3020-1.2/ LT3020-1.5/LT3020-1.8
U U W U APPLICATIO S I FOR ATIO
an output current change of 1mA to 100mA is typically 20 BOTH CAPACITORS ARE 16V, 0.4mV at V 1210 CASE SIZE, 10µF ADJ = 200mV. At VOUT = 1.5V, load regulation is: 0 (1.5V/200mV) • (0.4mV) = 3mV X5R –20
Output Capacitance and Transient Response
–40 The LT3020’s design is stable with a wide range of output –60 capacitors, but is optimized for low ESR ceramic capaci- CHANGE IN VALUE (%) Y5V tors. The output capacitor’s ESR affects stability, most –80 notably with small value capacitors. Use a minimum output capacitor of 2.2µF with an ESR of 0.3Ω or less to –100 0 2 4 6 8 10 12 14 16 prevent oscillations. The LT3020 is a low voltage device, DC BIAS VOLTAGE (V) and output load transient response is a function of output 3020 F02 capacitance. Larger values of output capacitance decrease
Figure 2. Ceramic Capacitor DC Bias Characteristics
the peak deviations and provide improved transient re- sponse for larger load current changes. For output capaci- tor values greater than 20µF a small feedforward capacitor 40 with a value of 300pF across the upper divider resistor (R2 20 in Figure 1) is required. 0 X5R Give extra consideration to the use of ceramic capacitors. –20 Manufacturers make ceramic capacitors with a variety of dielectrics, each with a different behavior across tempera- –40 Y5V ture and applied voltage. The most common dielectrics are –60 CHANGE IN VALUE (%) Z5U, Y5V, X5R and X7R. The Z5U and Y5V dielectrics –80 BOTH CAPACITORS ARE 16V, provide high C-V products in a small package at low cost, 1210 CASE SIZE, 10µF but exhibit strong voltage and temperature coefficients. –100 –50 –25 0 25 50 75 100 125 The X5R and X7R dielectrics yield highly stable TEMPERATURE (°C) characterisitics and are more suitable for use as the output 3020 F03 capacitor at fractionally increased cost. The X5R and X7R dielectrics both exhibit excellent voltage coefficient char-
Figure 3. Ceramic Capacitor Temperature Characteristics
acteristics. The X7R type works over a larger temperature range and exhibits better temperature stability whereas X5R is less expensive and is available in higher values. Figures 2 and 3 show voltage coefficient and temperature coefficient comparisons between Y5V and X5R material. Voltage and temperature coefficients are not the only 1mV/DIV sources of problems. Some ceramic capacitors have a piezoelectric response. A piezoelectric device generates voltage across its terminals due to mechanical stress, simi- lar to the way a piezoelectric accelerometer or microphone works. For a ceramic capacitor, the stress can be induced V 1ms/DIV 3020 F04 OUT = 1.3V by vibrations in the system or thermal transients. The re- COUT = 10µF I sulting voltages produced can cause appreciable amounts LOAD = 0 of noise. A ceramic capacitor produced Figure 4’s trace in
Figure 4. Noise Resulting from Tapping on a Ceramic Capacitor
3020fc 10
U U W U APPLICATIO S I FOR ATIO
an output current change of 1mA to 100mA is typically 20 BOTH CAPACITORS ARE 16V, 0.4mV at V 1210 CASE SIZE, 10µF ADJ = 200mV. At VOUT = 1.5V, load regulation is: 0 (1.5V/200mV) • (0.4mV) = 3mV X5R –20
Output Capacitance and Transient Response
–40 The LT3020’s design is stable with a wide range of output –60 capacitors, but is optimized for low ESR ceramic capaci- CHANGE IN VALUE (%) Y5V tors. The output capacitor’s ESR affects stability, most –80 notably with small value capacitors. Use a minimum output capacitor of 2.2µF with an ESR of 0.3Ω or less to –100 0 2 4 6 8 10 12 14 16 prevent oscillations. The LT3020 is a low voltage device, DC BIAS VOLTAGE (V) and output load transient response is a function of output 3020 F02 capacitance. Larger values of output capacitance decrease
Figure 2. Ceramic Capacitor DC Bias Characteristics
the peak deviations and provide improved transient re- sponse for larger load current changes. For output capaci- tor values greater than 20µF a small feedforward capacitor 40 with a value of 300pF across the upper divider resistor (R2 20 in Figure 1) is required. 0 X5R Give extra consideration to the use of ceramic capacitors. –20 Manufacturers make ceramic capacitors with a variety of dielectrics, each with a different behavior across tempera- –40 Y5V ture and applied voltage. The most common dielectrics are –60 CHANGE IN VALUE (%) Z5U, Y5V, X5R and X7R. The Z5U and Y5V dielectrics –80 BOTH CAPACITORS ARE 16V, provide high C-V products in a small package at low cost, 1210 CASE SIZE, 10µF but exhibit strong voltage and temperature coefficients. –100 –50 –25 0 25 50 75 100 125 The X5R and X7R dielectrics yield highly stable TEMPERATURE (°C) characterisitics and are more suitable for use as the output 3020 F03 capacitor at fractionally increased cost. The X5R and X7R dielectrics both exhibit excellent voltage coefficient char-
Figure 3. Ceramic Capacitor Temperature Characteristics
acteristics. The X7R type works over a larger temperature range and exhibits better temperature stability whereas X5R is less expensive and is available in higher values. Figures 2 and 3 show voltage coefficient and temperature coefficient comparisons between Y5V and X5R material. Voltage and temperature coefficients are not the only 1mV/DIV sources of problems. Some ceramic capacitors have a piezoelectric response. A piezoelectric device generates voltage across its terminals due to mechanical stress, simi- lar to the way a piezoelectric accelerometer or microphone works. For a ceramic capacitor, the stress can be induced V 1ms/DIV 3020 F04 OUT = 1.3V by vibrations in the system or thermal transients. The re- COUT = 10µF I sulting voltages produced can cause appreciable amounts LOAD = 0 of noise. A ceramic capacitor produced Figure 4’s trace in
Figure 4. Noise Resulting from Tapping on a Ceramic Capacitor
3020fc 10