LTC3026EMSE-1#PBF Linear Technology, LTC3026EMSE-1#PBF Datasheet - Page 11

• Manufacturer Part Number: LTC3026EMSE-1#PBF
• Description: 1.5a vldo in dfn... ic reg ldo adj 1.5a...
• Manufacturer: Linear Technology

operaTion
The LTC3026 operates at a relatively high gain of
270µV/A referred to the ADJ input. Thus, a load current
change of 1mA to 1.5A produces a 400µV drop at the ADJ
input. To calculate the change in the output, simply mul-
tiply by the gain of the feedback network (i.e. 1 + R2/R1).
For example, to program the output for 1.2V choose
R2/R1 = 2. In this example an output current change of
1mA to 1.5A produces –400µV • (1 + 2) = 1.2mV drop at
the output.
Power Good Operation
The LTC3026 includes an open-drain power good (PG)
output pin with hysteresis. If the chip is in shutdown or
under UVLO conditions (V
pedance to ground. PG becomes high impedance when
V
impedance until V
tion value. A pull-up resistor can be inserted between PG
and a positive logic supply (such as IN, OUT, BST, etc.)
to signal a valid power good condition. V
minimum operating voltage (1.14V) or greater for PG to
function correctly.
Output Capacitance and Transient Response
The LTC3026 is designed to be stable with a wide range
of ceramic output capacitors. The ESR of the output
capacitor affects stability, most notably with small ca-
pacitors. An output capacitor of 10µF or greater with an
ESR of 0.05Ω or less is recommended to ensure stability.
OUT
rises to 93% of its regulation voltage. PG stays high
Figure 4. Ceramic Capacitor DC Bias Characteristics
–100
–20
–40
–60
–80
20
0
0
OUT
1
falls back down to 91% of its regula-
DC BIAS VOLTAGE (V)
2
BOTH CAPACITORS ARE 10µF,
6.3V, 0805 CASE SIZE
Y5V
BST
3
X5R
< 4.25V), PG is low im-
4
5
IN
3026 F04
should be the
6
The LTC3026 is a micropower device and output transient
response will be a function of output capacitance. Larger
values of output capacitance decrease the peak deviations
and provide improved transient response for larger load
current changes. Note that bypass capacitors used to
decouple individual components powered by the LTC3026
will increase the effective output capacitor value. High
ESR tantalum and electrolytic capacitors may be used,
but a low ESR ceramic capacitor must be in parallel at the
output. There is no minimum ESR or maximum capacitor
size requirements.
Extra consideration must be given to the use of ceramic
capacitors. Ceramic capacitors are manufactured with a
variety of dielectrics, each with different behavior across
temperature and applied voltage. The most common di-
electrics used are Z5U, Y5V, X5R and X7R. The Z5U and
Y5V dielectrics are good for providing high capacitances
in a small package, but exhibit strong voltage and tem-
perature coefficients as shown in Figures 4 and 5. When
used with a 2V regulator, a 10µF Y5V capacitor can exhibit
an effective value as low as 1µF to 2µF over the operating
temperature range. The X5R and X7R dielectrics result in
more stable characteristics and are more suitable 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.
A minimum capacitance of 5µF must be maintained at all
times on the LTC3026 LDO output.
Figure 5. Ceramic Capacitor Temperature Characteristics
–100
–20
–40
–60
–80
20
0
–50
BOTH CAPACITORS ARE 10µF,
6.3V, 0805 CASE SIZE
–25
TEMPERATURE (°C)
0
25
Y5V
50
X5R
LTC3026
75
3026 F05
11
3026ff