LTC3388-3 Linear Technology, LTC3388-3 Datasheet - Page 17

• Manufacturer Part Number: LTC3388-3
• Description: 20V High Efficiency Nanopower Step-Down Regulator
• Manufacturer: Linear Technology

DataSheet.in
APPLICATIONS INFORMATION
Interfacing with a Microprocessor
The PGOOD, STBY, and EN pins can be useful when power-
ing a microprocessor from the LTC3388-1/LTC3388-3.
The PGOOD signal can be used to enable a sleeping micro-
processor or other circuitry when V
as shown in Figure 7. While active, a microprocessor may
draw a small load when operating sensors, and then draw a
large load to transmit data. Figure 7 shows the LTC3388-1/
LTC3388-3 responding smoothly to such a load step.
The microprocessor or other circuitry may require a quiet
supply for performing some functions. The STBY pin allows
the microprocessor to place the LTC3388-1/LTC3388-3 into
standby mode where the buck converter is inactive. Any
+
2.7V TO 4.2V
Li-ION
10μF
6V
V
V
EN
D1
CAP
D0
10μF
25V
IN
IN2
LTC3388-1
GND
1μF
6V
4.7μF
6V
PGOOD
Figure 8. Piezoelectric Energy Harvester and 1.2V Secondary Rail
Figure 7. 1.8V Step-Down Converter Powering a Microprocessor
with a Wireless Transmitter and 45mA Load Step Response
STBY
V
OUT
SW
PZ1
V
CAP
V
D1
D0
IN
IN2
OUT
MIDE V21BL
LTC3588-1
22μH
reaches regulation,
GND
PGOOD
V
PZ2
OUT
SW
1.8V
1M
47μF
6V
47μH
STBY
EN
CORE
MICROPROCESSOR
338813 F07a
GND
1M
3.3V
10μF
6V
ripple in the output voltage of the LTC3388-1/LTC3388-3
will cease and the output capacitor will support the load of
the microprocessor and other circuitry. While in standby
the output voltage will decrease as it’s loaded. The output
capacitor should be sized to minimize the decline.
The EN pin can be used to activate the LTC3388-1/LTC3388-3.
For instance, in Figure 8 the LTC3388-1 is enabled by the
PGOOD output of the LTC3588-1, a piezoelectric energy
harvesting power supply, to create a 1.2V rail. The quies-
cent current that the LTC3388-1 draws will appear at the
input of the LTC3588-1, reduced by the conversion ratio
of the LTC3588-1 buck converter. Because the LTC3388-1
is driven by a 3.3V supply no capacitors are needed for
the internal V
T
X
EN
V
V
CAP
D1
D0
IN2
IN
LTC3388-1/LTC3388-3
LTC3388-1
IN2
AC-COUPLED
GND
25mA/DIV
20mV/DIV
CURRENT
and CAP rails.
LOAD
PGOOD
V
0mA
OUT
STBY
V
OUT
SW
V
L = 22μH, C
LOAD STEP BETWEEN 5mA AND 50mA
IN
= 5.5V
22μH
338813 F07
OUT
= 100μF
250μs/DIV
1.2V
47μF
6V
338813 F07b
17
338813f