DN465 - Ultralow Power Boost Converters Require Only 8.5μA of Standby Quiescent Current

Ultralow Power Boost Converters Require Only 8.5µA of Standby
Quiescent Current
Design Note 465
Xiaohua Su
Introduction
Industrial remote monitoring systems and keep-alive
circuits spend most of their time in standby mode. Many
of these systems also depend on battery power, so power
supply efficiency in standby state is very important to
maximize battery life. The LT®8410/-1 high efficiency
boost converter is ideal for these systems, requiring
only 8.5μA of quiescent current in standby mode. The
device integrates high value (12.4M/0.4M) output feedback resistors, significantly reducing input current when
the output is in regulation with no load. Other features
include an integrated 40V switch and Schottky diode,
output disconnect with current limit, built in soft-start,
overvoltage protection and a wide input range, all in a
tiny 8-pin 2mm × 2mm DFN package.
Application Example
Figure 1 details the LT8410 boost converter generating a 16V output from a 2.5V-to-16V input source. The
LT8410/-1 controls power delivery by varying both the
peak inductor current and switch off time. This control
scheme results in low output voltage ripple as well as high
efficiency over a wide load range. Figures 2 and 3 show
efficiency and output peak-to-peak ripple for Figure 1’s
circuit. Output ripple voltage is less than 10mV despite
the circuit’s small (0.1μF) output capacitor.
The soft-start feature is implemented by connecting an
external capacitor to the VREF pin. If soft-start is not
needed, the capacitor can be removed. Output voltage
is set by a resistor divider from the VREF pin to ground
with the center tap connected to the FBP pin, as shown
in Figure 1. The FBP pin can also be biased directly by
an external reference.
The SHDN pin of the LT8410/-1 can serve as an on/off
switch or as an undervoltage lockout via a simple resistor
divider from VCC to ground.
Ultralow Quiescent Current Boost Converter with
Output Disconnect
Low quiescent current in standby mode and high value
integrated feedback resistors allow the LT8410/-1 to
regulate a 16V output at no load from a 3.6V input with
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
100
VIN = 12V
90
VIN
2.5V to 16V
2.2μF
0.1μF
SW
VCC
CHIP
ENABLE
CAP
VOUT = 16V
VOUT
LT8410
VREF
SHDN
0.1μF*
604K
GND
0.1μF
FBP
412K
*HIGHER VALUE CAPACITOR IS REQUIRED
WHEN THE VIN IS HIGHER THAN 5V
8410-1 TA01a
Figure 1. 2.5V-16V To 16V Boost Converter
05/09/465
EFFICIENCY (%)
100μH
VIN = 5V
80
VIN = 3.6V
70
60
50
40
0.01
0.1
1
10
LOAD CURRENT (mA)
100
8410-1 TA03
Figure 2. Efficiency vs Load Current For Figure 1 Converter
about 30μA of average input current. Figures 4, 5 and 6
show typical quiescent and input currents in regulation
with no load.
The device also integrates an output disconnect PMOS,
which blocks the output load from the input during
shutdown. The maximum current through the PMOS is
limited by circuitry inside the chip, allowing it to survive
output shorts.
Compatible with High Impedance Batteries
A power source with high internal impedance, such as a
coin cell battery, may show normal output on a voltmeter,
but its voltage can collapse under heavy current demands.
This makes it incompatible with high current DC/DC
converters. With very low switch current limits (25mA
for the LT8410 and 8mA for the LT8410-1), the LT8410/-1
can operate very efficiently from high impedance sources
without causing inrush current problems. This feature also
helps preserve battery life.
Conclusion
The LT8410/-1 is a smart choice for applications which
require low standby quiescent current and/or require low
input current, and is especially suited for power supplies
with high impedance sources. The ultralow quiescent
current and high value integrated feedback resistors keep
average input current very low, significantly extending battery operating time. The LT8410/-1 is packed with features
without compromising performance or ease of use and is
available in a tiny 8-pin 2mm × 2mm package.
10
10
8
QUIESCENT CURRENT (μA)
VOUT PEAK-TO-PEAK RIPPLE (mV)
VIN = 3.6V
6
4
2
8
6
4
2
VCC = 3.6V
0
0.01
0.1
1
LOAD CURRENT (mA)
0
–40
10
8410-1 TA02
0
40
80
TEMPERATURE (°C)
120
8410-1 G06
Figure 3. Output Peak-to-Peak Ripple vs Load
Current for Figure 1 Converter at 3.6V
Figure 4. Quiescent Current vs Temperature
(Not Switching)
1000
12
VCC = 3.6V
AVERAGE INPUT CURRENT (μA)
QUIESCENT CURRENT (μA)
10
8
6
4
2
0
100
10
0
4
8
12
VCC VOLTAGE (V)
16
8410-1 G05
Figure 5. Quiescent Current vs VCC Voltage
(Not Switching)
Data Sheet Download
www.linear.com
0
10
20
30
OUTPUT VOLTAGE (V)
40
8410-1 G08
Figure 6. Average Input Current in
Regulation with No Load
For applications help,
call (719) 593-1579, Ext. 245
Linear Technology Corporation
dn465 LT/TP 0509 155K • PRINTED IN THE USA
FAX: (408) 434-0507 ● www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2009
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
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