LTC3446 Datasheet, PDF (18/20 Pages) Linear Technology – Monolithic Buck Regulator with Dual VLDO Regulators

LTC3446
APPLICATIONS INFORMATION
20
BOTH CAPACITORS ARE 1μF,
10V, 0603 CASE SIZE
0
X5R
–20
–40
Y5V
–60
–80
–100
0
2
4
6
8
10
DC BIAS VOLTAGE (V)
3446 F03
Figure 3. Ceramic Capacitor DC Bias Characteristics
in more stable characteristics and are usually more suit-
able for use as the output capacitor. The X7R type has
better stability across temperature, while the X5R is less
expensive and is available in higher values. In all cases,
the output capacitance should never drop below 0.4μF, or
instability or degraded performance may occur.
VLDO Output Short-Circuit Protection
The VLDO regulators have built-in short-circuit limiting.
During short-circuit conditions, internal circuitry automati-
cally limits the output current to approximately 760mA.
20
0
X5R
–20
Y5V
–40
–60
–80
BOTH CAPACITORS ARE 1μF,
10V, 0603 CASE SIZE
–100
–50 –25 0
25 50
TEMPERATURE (°C)
75
3446 F04
Figure 4. Ceramic Capacitor Temperature Characteristics
VLDO Regulator Soft-Start
Each VLDO regulator includes a soft-start feature to
prevent excessive current flow during start-up. When
the VLDO regulator is enabled, the soft-start circuitry
gradually increases the VLDO regulator reference voltage
from 0V to 0.4V over a period of about 600μs. There is a
short 700μs delay from the time the part is enabled until
the LDO output starts to rise. Figure 5 shows the start-up
output waveform.
1.5V VLDO OUTPUT
1.2V VLDO OUTPUT
0.5V/DIV
BOTH VLDO
ENABLES
5V/DIV
V_LVIN = 1.8V
200μs/DIV
V_IN = 3.6V
FRONT PAGE APPLICATION CIRCUIT
WITH 10mA RESISTOR LOADS ON
EACH VLDO OUTPUT
3446 F05
Figure 5. VLDO Regulator Output Start-Up
3446fd
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