LP5952TL-0.7 NSC [National Semiconductor], LP5952TL-0.7 Datasheet - Page 11

• Manufacturer Part Number: LP5952TL-0.7
• Description: 350mA Dual Rail Linear Regulator
• Manufacturer: NSC [National Semiconductor]

Application Hints
DUAL RAIL SUPPLY
The LP5952 requires two different supply voltages:
•V
voltage
•V
It's important that V
the device is used in the typical post regulation application as
shown in FIGURE 1, the sequencing of the two power sup-
plies is not an issue as V
regulator and the LP5952. The output voltage of the DC-DC
regulator will take some time to rise up and supply V
LP5952. In this application V
slowly than V
In case V
pins will ramp up simultaneously causing no problem.
Only in applications with two independent supplies connected
to the LP5952 special care must be taken to guarantee that
V
POWER DISSIPATION AND DEVICE OPERATION
The permissible power dissipation for any package is a mea-
sure of the capability of the device to pass heat from the power
source, the junctions of the IC, to the ultimate heat sink, the
ambient environment. Thus the power dissipation is depen-
dent on the ambient temperature and the thermal resistance
across the various interfaces between the die and ambient
air.
As stated in the electrical specification section, the allowable
power dissipation for the device in a given package can be
calculated using the equation:
P
With a θ
package returns a value of 1053mW with a maximum junction
temperature of 125°C at T
The actual power dissipation across the device can be esti-
mated by the following equation:
P
This establishes the relationship between the power dissipa-
tion allowed due to thermal consideration, the voltage drop
across the device, and the continuous current capability of the
device. These two equations should be used to determine the
optimum operating conditions for the device in the application.
As an example, to keep full load current capability of 350mA
for a 1.5V output voltage option at a high ambient temperature
of 85°C, V
V
The figure below shows the output current derating due to
these considerations:
IN
D
D
IN
IN
BATT
= (T
= (V
is always
≤
, the power input voltage, is regulated to the fixed output
P
, the bias input voltage, supplies internal circuitry.
J(MAX)
IN
D
JA
IN
/ I
- V
IN
OUT
= 95°C/W, the device in the 5 bump micro SMD
is shorted to V
has to be kept
OUT
BATT
- T
≤
+ V
V
) * I
A
BATT
) / θ
.
OUT
OUT
IN
JA
.
does not exceed V
= 421mW / 350mA + 1.5V = 2.7V.
BATT
A
≤
of 25°C or 421mW at T
BATT
, the voltages at the two supply
2.7V:
IN
supplies both, the DC-DC
will always ramp up more
BATT
at any time. If
A
of 85°C.
IN
of
11
The typical contribution of the bias input voltage supply
V
P
EXTERNAL CAPACITORS
As is common with most regulators, the LP5952 requires ex-
ternal capacitors to ensure stable operation. The LP5952 is
specifically designed for portable applications requiring mini-
mum board space and the smallest size components. These
capacitors must be correctly selected for good performance.
INPUT CAPACITOR
If the LP5952 is used stand alone, an input capacitor at V
required for stability. It is recommended that a 1.0µF capacitor
be connected between the LP5952 power voltage input pin
V
without limit).
This capacitor must be located a distance of not more than 1
cm from the V
Any good quality ceramic, tantalum, or film capacitor may be
used at the input.
A capacitor at V
ply does not exceed 5cm.
If the device is used in the typical application as post regulator
after a DC-DC regulator, no input capacitors are required at
all as the capacitors of the DC-DC regulator (C
are sufficient if both components are mounted close to each
other and a proper GND plane is used. If the distance between
the output capacitor of the DC-DC regulator and the V
of the LP5952 is larger than 5cm, it's recommended to add
the mentioned input capacitor at V
Important: Tantalum capacitors can suffer catastrophic fail-
ures due to surge current when connected to a low-
impedance source of power (like a battery or a very large
capacitor). If a tantalum capacitor is used at the input, it must
be guaranteed by the manufacturer to have a surge current
rating sufficient for the application.
The ESR (Equivalent Series Resistance) of the input capac-
itor should be in the range of 3mΩ to 300mΩ. The tolerance
and temperature coefficient must be considered when select-
ing the capacitor to ensure the capacitance will remain
470nF over the entire operating temperature range.
BATT
D_VBATT
IN
FIGURE 6: Maximum Load Current vs V
and ground (this capacitance value may be increased
to the power dissipation can be neglected:
= V
BATT
85°C, V
IN
pin and returned to a clean analogue ground.
BATT
* I
QVBATT
is not required if the distance to the sup-
OUT
= 1.5V, θ
= 5.5V * 50µA = 0.275mW typical.
JA
IN
.
= 95°C/W
IN
- V
IN
www.national.com
OUT
and C
, T
20208508
IN
A
OUT
IN
=
pin
is
≥
)