Lt1339 Design Manual

Linear Technology Corporation

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appnote circuit ,Schematic
Application Note 73
High Power Synchronous
DC/DC Controller
FEATURES
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DESCRIPTION
The LT
®
1339 is a high power synchronous current mode
Switching Regulator controller. The IC drives dual
N-Channel MOSFETs to create a single IC solution for high
power DC/DC converters in applications up to 60V.
The LT1339 incorporates programmable average current
limiting, allowing accurate limiting of DC load current
independent of Inductor ripple current. The IC also incor-
porates user-adjustable slope compensation for minimi-
zation of magnetics at duty cycles up to 90%.
The LT1339 timing Oscillator operating frequency is pro-
grammable and can be synchronized up to 150kHz. Mini-
mum off-time operation provides main switch protection.
The IC also incorporates a soft start feature that is gated by
both shutdown and undervoltage lockout conditions.
An output phase reversal pin allows flexibility in configu-
ration of converter types, including inverting and negative
topologies.
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High Voltage: Operation Up to 60V
High Current: Dual N-Channel Synchronous Drive
Handles Up to 10,000pF Gate Capacitance
Programmable Average Load Current Limiting
5V Reference Output with 10mA External
Loading Capability
Programmable Fixed Frequency Synchronizable
Current Mode Operation Up to 150kHz
Undervoltage Lockout with Hysteresis
Programmable Start Inhibit for Power Supply
Sequencing and Protection
Adaptive Nonoverlapping Gate Drive Prevents
Shoot-Through
APPLICATIONS
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48V Telecom Power Supplies
Personal Computers and Peripherals
Distributed Power Converters
Industrial Control Systems
Lead-Acid Battery Backup Systems
Automotive and Heavy Equipment
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATION
28V to 5V 20A Buck Converter
DBST
IN5819
SYNC
5V
REF
V
BOOST
V
IN
28V
+
+
R
CT
10k
C
AVG
C
CT
2200PF 2200pF
C
SS
, 1µF
C
VC
, 1nF
CT
SL/ADJ
I
AVG
TG
TS
12V
IN
BG
PGND
PHASE
V
C
SGND
V
FB
V
REF
R
FB2
1k
SENSE
R
FB1
3k
RUN/SHDN
SENSE
+
+
CBST
1µF
D1
12V
C
12VIN
47µF
+
C
IN
1500µF
63V
×
3
EFFICIENCY (%)
C
5VREF
1µF
D2
R
RUN
×
2
L1
10µH
+
SS
R
VC
, 10k
C
REF
0.1µF
R
S
0.005Ω
+
L1 = CTX02-13400-X2
C
OUT
5V AT 20A
2200µF
6.3V
×
2
1339 TA03
AN73-6
U
U
U
28V to 5V Efficiency
100
90
80
70
60
50
0
10
5
15
OUTPUT CURRENT (A)
20
1339 TA03a
V
OUT