User's Manual

TOBY-R2 series - System Integration Manual
UBX-16010572 - R04 Design-in
Page 70 of 147
2.2.1.3 Guidelines for VCC supply circuit design using a Low Drop-Out linear regulator
The use of a linear regulator is suggested when the difference from the available supply rail source and the VCC
value is low. The linear regulators provide high efficiency when transforming a 5 VDC supply to a voltage value
within the module VCC normal operating range.
The characteristics of the Low Drop-Out (LDO) linear regulator connected to VCC pins should meet the following
prerequisites to comply with the module VCC requirements summarized in Table 6:
 Power capabilities: the LDO linear regulator with its output circuit must be capable of providing a voltage
value to the VCC pins within the specified operating range and must be capable of delivering to VCC pins
the maximum peak / pulse current consumption during Tx burst at maximum Tx power specified in TOBY-R2
series Data Sheet [1].
 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 max 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 should be
carefully evaluated, as the VCC voltage must ramp from 2.3 V to 2.8 V in less than 4 ms to switch on the
modules by applying VCC supply. The modules can be otherwise switched on by forcing a low level on the
RESET_N pin during the VCC rising edge and then releasing the RESET_N pin when the VCC supply voltage
stabilizes at its proper nominal value.
Figure 30 and the components listed in Table 21 show an example of a power supply circuit, where the VCC
module supply is provided by an LDO linear regulator capable of delivering the required current, with proper
power handling capability.
It is recommended to configure the LDO linear regulator to generate a voltage supply value slightly below the
maximum limit of the module VCC normal operating range (e.g. ~4.1 V for the VCC, as in the circuits described
in Figure 30 and Table 21). This reduces the power on the linear regulator and improves the thermal design of
the circuit.
5V
C1 R1
IN OUT
ADJ
GND
1
2
4
5
3
C2R2
R3
U1
SHDN
TOBY-R2 series
71
VCC
72
VCC
70
VCC
GND
C3
Figure 30: Example of high reliability VCC supply application circuit using an LDO linear regulator
Reference
Description
Part Number - Manufacturer
C1, C2
10 µF Capacitor Ceramic X5R 0603 20% 6.3 V
GRM188R60J106ME47 - Murata
C3
330 µF Capacitor Tantalum D_SIZE 6.3 V 45 m
T520D337M006ATE045 - KEMET
R1
47 k Resistor 0402 5% 0.1 W
RC0402JR-0747KL - Yageo Phycomp
R2
9.1 k Resistor 0402 5% 0.1 W
RC0402JR-079K1L - Yageo Phycomp
R3
3.9 k Resistor 0402 5% 0.1 W
RC0402JR-073K9L - Yageo Phycomp
U1
LDO Linear Regulator ADJ 3.0 A
LT1764AEQ#PBF - Linear Technology
Table 21: Components for high reliability VCC supply application circuit using an LDO linear regulator