Integration Manual

LISA-U2 series - System Integration Manual
UBX-13001118 - R25 System description Page 24 of 182
Low Drop-Out (LDO) linear regulator
The characteristics of the LDO linear regulator connected to the VCC pins should meet the following
requirements:
 Power capabilities: the LDO linear regulator with its output circuit must be capable of providing a
proper voltage value to the VCC pins and of delivering 2.5 A current pulses with 1/8 duty cycle.
 Power dissipation: the power handling capability of the LDO linear regulator must be checked to
limit its junction temperature to the maximum rated operating range (i.e. check the voltage drop
from the maximum input voltage to the minimum output voltage to evaluate the power dissipation
of the regulator).
 Output voltage slope: the use of the soft start function provided by some voltage regulators must
be carefully evaluated, since the voltage at the VCC pins must ramp from 2.5 V to 3.2 V within 1
ms to allow a proper switch-on of the module.
Figure 8 and the components listed in Table 9 show an example of a power supply circuit where the
VCC module supply is provided by an LDO linear regulator capable of delivering 2.5 A current pulses,
with appropriate power handling capability. The use of a linear regulator is suggested when the
difference from the available supply rail and the VCC value is low: linear regulators provide high
efficiency when transforming a 5 V supply to a voltage value within the module VCC normal operating
range.
It is recommended to configure the LDO linear regulator so that it generates a voltage supply value
slightly below the maximum limit of the module VCC normal operating range (e.g. ~4.1 V as in the
circuit described in Figure 8 and Table 9). This reduces the power on the linear regulator and improves
the thermal design of the supply circuit.
5V
C1 R1
IN OUT
ADJ
GND
1
2
4
5
3
C2R2
R3
U1
SHDN
LISA-U2 series
62
VCC
63
VCC
61
VCC
GND
C3
Figure 8: Suggested schematic design for the VCC voltage supply application circuit using an LDO linear regulator
Reference
Description
Part Number - Manufacturer
C1, C2
10 µ F Capacitor Ceramic X5R 0603 20% 6.3 V
GRM188R60J106ME47 - Murata
C3
330 µ F Capacitor Tantalum D_SIZE 6.3 V 45 mΩ
T520D337M006ATE045 - KEMET
R1
47 kΩ Resistor 0402 5% 0.1 W
RC0402JR-0747KL - Yageo Phycomp
R2
9.1 kΩ Resistor 0402 5% 0.1 W
RC0402JR-079K1L - Yageo Phycomp
R3
3.9 kΩ Resistor 0402 5% 0.1 W
RC0402JR-073K9L - Yageo Phycomp
U1
LDO Linear Regulator ADJ 3.0 A
LT1764AEQ#PBF - Linear Technology
Table 9: Suggested components for VCC voltage supply application circuit using an LDO linear regulator