Datasheet

LTC3523/LTC3523-2
12
3523fb
DUAL BUCK-BOOST AND STEP-UP CONVERTER
OPERATION
The LTC3523/LTC3523-2 can be operated in a cascaded
confi guration as shown in Figure 2, allowing buck-boost
and step-up converter operation. Supply rail sequencing
is achieved by feeding the step-up converter PGOOD1
into the step-down’s SHDN2 pin. Note that the overall
3.3V converter effi ciency is the product of the individual
effi ciencies.
V
IN1
SW1 SW2
FB2
MODE
PGOOD2
SHDN2
FB1
V
IN
PGOOD1
SHDN1
V
OUT
10pF
10μF
V
OUT2
STEP-DOWN
OUTPUT
3.3V
50mA
825k
182k
V
IN
3523 F02a
768k
243k
100k
4.7μH
10μH
V
IN2
LTC3523
V
BAT
GND1 GND2 GND3
4.7μF
V
IN
1.8V TO 5.25V
V
OUT1
STEP-UP
OUTPUT
5V
100mA
10μF
OFF ON
Figure 2. Dual Converter Effi ciency (Load Applied
to Step-Down Output)
APPLICATIONS INFORMATION
OUTPUT CURRENT (mA)
0.1
0
EFFICIENCY (%)
10
30
40
50
100
70
1
10
3523 F02b
20
80
90
60
100
1000
3.3V OUTPUT
5V OUTPUT
V
IN
= 2.4V
V
OUT1
= 5V
V
OUT2
= 3.3V
f
OSC
= 1.2MHz
BURST ENABLED