LTM8047
9
8047fc
For more information www.linear.com/LTM8047
APPLICATIONS INFORMATION
For most applications, the design process is straight-
forward, summarized as follows:
1. Look at Table 1 and find the row that has the desired
input range and output voltage.
2. Apply the recommended C
IN
, C
OUT
and R
ADJ
.
3. Connect BIAS as indicated, or tie to an external source
up to 15V or V
IN
, whichever is less.
While these component combinations have been tested for
proper operation, it is incumbent upon the user to verify
proper operation over the intended system’s line, load and
environmental conditions. Bear in mind that the maximum
output current may be limited by junction temperature,
the relationship between the input and output voltage
magnitude and polarity and other factors. Please refer
to the graphs in the Typical Performance Characteristics
section for guidance.
Capacitor Selection Considerations
The C
IN
and C
OUT
capacitor values in Table 1 are the
minimum recommended values for the associated oper-
ating conditions. Applying capacitor values below those
indicated in T
able 1 is not recommended, and may result
in undesirable operation. Using larger values is generally
acceptable, and can yield improved dynamic response, if
it is necessar
y. Again, it is incumbent upon the user to
verify proper operation over the intended system’s line,
load and environmental conditions.
Ceramic capacitors are small, robust and have very low
ESR. However, not all ceramic capacitors are suitable.
X5R and X7R types are stable over temperature and ap
-
plied voltage and give dependable service. Other types,
including Y5V and Z5U have very large temperature and
voltage coefficients of capacitance. In an application cir
-
cuit they may have only a small fraction of their nominal
capacitance resulting in much higher output voltage ripple
than expected.
A final precaution regarding ceramic capacitors concerns
the maximum input voltage rating of the LTM8047. A
ceramic input capacitor combined with trace or cable
inductance
forms a high-Q (underdamped) tank circuit. If
the LTM8047 circuit is plugged into a live supply, the input
voltage can ring to much higher than its nominal value,
possibly exceeding the device’s rating. This situation is
easily avoided; see the Hot-Plugging Safely section.
LTM8047 Table 1. Recommended Component Values and Configuration for Specific V
OUT
Voltages (T
A
= 25°C)
V
IN
V
OUT
V
BIAS
C
IN
C
OUT
R
ADJ
3.1V to 32V 2.5V 3.1V to 15V or Open 2.2µF, 50V, 1206 100µF, 6.3V, 1210 12.4k
3.1V to 32V 3.3V 3.1V to 15V or Open 2.2µF, 50V, 1206 100µF, 6.3V, 1210 10k
3.1V to 29V 5V 3.1V to 15V or Open 2.2µF, 50V, 1206 22µF, 16V, 1210 6.98k
3.1V to 26V 8V 3.1V to 15V or Open 2.2µF, 50V, 1206 22µF, 10V, 1206 4.53k
3.1V to 24V 12V 3.1V to 15V or Open 2.2µF, 25V, 0805 10µF, 16V, 1210 3.16k/12pF*
9V to 15V 2.5V V
IN
2.2µF, 50V, 1206 100µF, 6.3V, 1210 12.4k
9V to 15V 3.3V V
IN
2.2µF, 50V, 1206 47µF, 6.3V, 1210 10k
9V to 15V 5V V
IN
2.2µF, 50V, 1206 22µF, 16V, 1210 6.98k
9V to 15V 8V V
IN
2.2µF, 50V, 1206 22µF, 10V, 1206 4.53k
9V to 15V 12V V
IN
2.2µF, 25V, 0805 10µF, 16V, 1210 3.16k
18V to 32V 2.5V 3.1V to 15V or Open 2.2µF, 50V, 1206 100µF, 6.3V, 1210 12.4k
18V to 32V 3.3V 3.1V to 15V or Open 2.2µF, 50V, 1206 47µF, 6.3V, 1210 10k
18V to 29V 5V 3.1V to 15V or Open 2.2µF, 50V, 1206 22µF, 16V, 1210 6.98k
18V to 26V 8V 3.1V to 15V or Open 2.2µF, 50V, 1206 22µF, 10V, 1206 4.53k
18V to 24V 12V 3.1V to 15V or Open 2.2µF, 50V, 1206 10µF, 16V, 1210 3.16k/12pF*
Note:
Do not allow BIAS to exceed V
IN
, a bulk input capacitor is required.
*Connect 3.16k in parallel with 12pF from ADJ to GND.
