LT3022 LINER [Linear Technology], LT3022 Datasheet - Page 10

• Manufacturer Part Number: LT3022
• Description: 1A, 0.9V to 10V, Very Low Dropout Linear Regulator
• Manufacturer: LINER [Linear Technology]

LT3022
applicaTions inForMaTion
Table 1 shows 1% resistor divider values for some common
output voltages with a resistor divider current equaling or
about 1mA.
Table 1
Output Capacitance and Transient Response
The LT3022’s design is stable with a wide range of output
capacitors, but is optimized for low ESR ceramic capacitors.
The output capacitor’s ESR affects stability, most notably
with small value capacitors. Use a minimum output ca-
pacitor of 10µF with an ESR of less than 0.1Ω to prevent
oscillations. The LT3022 is a low voltage device and output
load transient response is a function of output capacitance.
Larger values of output capacitance decrease the peak
deviations and provide improved transient response for
large load current changes.
Ceramic capacitors require extra consideration. Manufac-
turers make ceramic capacitors with a variety of dielectrics;
each with a different behavior across temperature and
applied voltage. The most common dielectrics are Z5U,
Y5V, X5R and X7R. Z5U and Y5V dielectrics provide high
C-V products in a small package at low cost, but exhibit
strong voltage and temperature coefficients. X5R and
X7R dielectrics yield highly stable characteristics and are
more suitable for use as the output capacitor at fractionally
increased cost. X5R and X7R dielectrics both exhibit excel-
lent voltage coefficient characteristics. X7R 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.
0
V
OUT
0.9
1.0
1.2
1.5
1.8
2.5
3.3
(V)
R1 (Ω)
200
187
200
200
187
187
200
R2 (Ω)
1000
1300
1500
2150
3090
698
750
Voltage and temperature coefficients are not the only
sources of problems. Some ceramic capacitors have a
piezoelectric response. A piezoelectric device generates
voltage across its terminals due to mechanical stress,
similar to the way a piezoelectric accelerometer or micro-
phone works. For a ceramic capacitor, the stress can be
induced by vibrations in the system or thermal transients.
The resulting voltages produced can cause appreciable
amounts of noise. A ceramic capacitor produced Figure 4’s
trace in response to light tapping from a pencil. Similar
vibration induced behavior can masquerade as increased
output voltage noise.
Figure 3. Ceramic Capacitor Temperature Characteristics
Figure 2. Ceramic Capacitor DC Bias Characteristics
–100
–100
–20
–40
–60
–80
–20
–40
–60
–80
20
40
20
0
0
–50
0
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10µF
2
–25
4
DC BIAS VOLTAGE (V)
0
TEMPERATURE (°C)
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10µF
6
25
8
Y5V
X5R
50
10
Y5V
75
12
X5R
100
14
3022 F02
3022 F03
16
125
3022f