LTC3355
1
3355fb
For more information www.linear.com/LTC3355
TYPICAL APPLICATION
FEATURES DESCRIPTION
20V 1A Buck DC/DC with
Integrated SCAP Charger
and Backup Regulator
The LTC
®
3355 is a complete input power interrupt ride-
through DC/DC system. The part charges a supercapacitor
while delivering load current to V
OUT
, and uses energy from
the supercapacitor to provide continuous V
OUT
backup
power when V
IN
power is lost. The LTC3355 contains a
nonsynchronous constant frequency current
mode mono-
lithic 1A buck switching regulator to provide a 2.7V to 5V
regulated output voltage from an input supply of up to 20V.
A 1A programmable CC/CV linear charger charges the
supercapacitor from V
OUT
. When the V
IN
supply drops
below the PFI threshold, the devices’s constant frequency
nonsynchronous current mode 5A boost switching
regulator delivers power from the supercapacitor to V
OUT
.
A
thermal regulation loop maximizes charge current while
limiting the die temperature to 110°C. The IC has boost,
charger and V
IN
programmable current limits. The LTC3355
is available in a 20-lead 4mm × 4mm QFN surface mount
package.
Supercapacitor Charger and Ride-Through Power Supply
Backup Operation
APPLICATIONS
n
V
IN
Voltage Range: 3V to 20V
n
V
OUT
Voltage Range: 2.7V to 5V
n
1A Current Mode Buck Main Regulator
n
5A Boost Backup Regulator Powered from Single
Supercapacitor
n
Boost Regulator Operates Down to 0.5V for
Maximum Utilization of Supercapacitor Energy
n
Programmable Supercapacitor Charge Current to
1A with Overvoltage Protection
n
Charger Supports Single Cell CC/CV Battery Charging
n
Programmable V
IN
Current Limit
n
Programmable Boost Current Limit
n
V
IN
Power Fail Indicator
n
V
CAP
Power Good Indicator
n
V
OUT
Power On Reset Output
n
Compact 20-Lead 4mm × 4mm QFN Package
n
Ride-Through “Dying Gasp” Supplies
n
Power Meters/Industrial Alarms/Solid State Drives
L, LT , LT C , LT M, Linear Technology, the Linear logo and Burst Mode are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their respective
owners.
200k60.4k1µF
V
INS
V
IN
1µF10µF10µF
2.4V
SCAP
1F TO 50F
47µF
V
OUT
4V
1A (MAX)
V
IN
12V
0.091Ω
2.49M
200k
402k
4.7pF
100k
4
5 7
V
INM5
6
PFI
BUCKPFO
BOOST
SW1
6.8µH
3.3µH
15
V
OUT
2
FB
14
V
CAP
16
17
11
SW2
CFB
19
10
13
9
8
3
20
V
CBST
I
BSTPK
12
I
CHG
LTC3355
PFOB
RSTB
CPGOOD
EN_CHG
MODE
18
INTV
CC
1A
665k
332k
3355 TA01a
154k
220pF
1
TIME (SECONDS)
0
8
10
14
15
3355 TA01b
6
4
5 10 20
2
0
12
V
IN
V
OUT
V
CAP
VOLTAGE (V)
CAPACITOR = 3F
I
VOUT
= 0.125A
