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PDF LT1339 Data sheet ( Hoja de datos )
| Número de pieza | LT1339 | |
| Descripción | High Power Synchronous DC/DC Controller | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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FEATURES
s High Voltage: Operation Up to 60V
s High Current: Dual N-Channel Synchronous Drive
Handles Up to 10,000pF Gate Capacitance
s Programmable Average Load Current Limiting
s 5V Reference Output with 10mA External
Loading Capability
s Programmable Fixed Frequency Synchronizable
Current Mode Operation Up to 150kHz
s Undervoltage Lockout with Hysteresis
s Programmable Start Inhibit for Power Supply
Sequencing and Protection
s Adaptive Nonoverlapping Gate Drive Prevents
Shoot-Through
U
APPLICATIONS
s 48V Telecom Power Supplies
s Personal Computers and Peripherals
s Distributed Power Converters
s Industrial Control Systems
s Lead-Acid Battery Backup Systems
s Automotive and Heavy Equipment
LT1339
High Power Synchronous
DC/DC Controller
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.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATION
+
C5VREF
1µF
RCT
10k
CCT CAVG
2200pF 2200pF
CVC, 1nF
CSS, 1µF
+
RVC, 10k
CREF
0.1µF
RFB2
1k
28V to 5V 20A Buck Converter
SYNC
VBOOST
5VREF
TG
CT TS
SL/ADJ
12VIN
LT1339 BG
IAVG
SS PGND
PHASE
VC RUN/SHDN
SGND
SENSE+
DBST
IN5819
+ CBST
1µF
D1
MBR0520
RRUN
100k
D2
MBR0520
+
12V
C12VIN
47µF
VIN
28V
IRL3803
IRL3103D2
×2
VFB
VREF
SENSE–
RFB1
3k
L1 = CTX02-13400-X2
+
CIN
1500µF
63V
×3
100
90
80
L1
10µH
70
60
50
0
RS
0.005Ω VOUT
+
COUT 5V AT 20A
2200µF
6.3V
×2
1339 TA03
28V to 5V Efficiency
5 10 15
OUTPUT CURRENT (A)
20
1339 TA03a
1
1 page  
TYPICAL PERFORMANCE CHARACTERISTICS
LT1339
Soft Start Charge Current
vs Temperature
9
RUN/SHDN Rising Threshold
vs Temperature
1.26
RUN/SHDN Threshold Hysteresis
vs Temperature
26
1.25 25
8 1.24
24
1.23 23
7 1.22
22
1.21 21
6
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
1339 G10
Bottom Gate Transition Times vs
Bottom Gate Capacitance
160
TA = 25°C
140
120
100
80
RISE TIME
60
FALL TIME
40
20
0
1000
2500
5000
7500 10000
BOTTOM GATE CAPACITANCE (pF)
1339 G13
1.20
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
1339 G11
Top Gate Transition Times vs
Top Gate Capacitance
300
TA = 25°C
250
200
RISE TIME
150
100
FALL TIME
50
0
1000
2500
5000
7500
TOP GATE CAPACITANCE (pF)
10000
1339 G14
20
–50 –25
0 25 50 75 100 125
TEMPERATURE (°C)
1339 G12
Average Current Limit Threshold
Sense Voltage Tolerance vs
Common Mode Voltage
160
FULL OPERATING
150 TEMPERATURE RANGE
140
UPPER LIMIT
130
TYPICAL
120
LOWER LIMIT
110
100
90
80
0 12345
VSENSE(CM) (V)
60
1339 G15
12VIN Supply Current vs
Supply Voltage
30
fO = 100kHz
28 TA = 25°C
26 CBG = 10000pF
24
22
20 CBG = 4700pF
18 CBG = 3300pF
16 CBG = 1000pF
14
10
11 12 13 14 15
12VIN SUPPLY VOLTAGE (V)
1339 G16
Boost Supply Current vs
12VIN Supply Voltage
18
fO = 100kHz
16 TA = 25°C
14 CTG = 10000pF
12
10
CTG = 4700pF
8
6
CTG = 1000pF
4
CTG = 3300pF
2
10 11 12 13 14 15
12VIN SUPPLY VOLTAGE (V)
1339 G17
5
5 Page 
LT1339
APPLICATIONS INFORMATION
impedance of the IAVG pin. The integrator corner fre-
quency is typically set 1 to 2 orders of magnitude below the
oscillator frequency and follows the relation:
f–3dB = (3.2)(10–6)/CAVG
The average current limit function can be disabled by
shorting the IAVG pin directly to SGND.
Soft Start Programming
The current control pin (VC) limits sensed inductor current
to zero at voltages less than a transistor VBE, to full average
current limit at VC = VBE + 1.8V. This generates a 1.8V full
regulation range for average load current. An internal
voltage clamp forces the VC pin to a VBE – 100mV above
the SS pin voltage. This 100mV “dead zone” assures 0%
duty cycle operation at the start of the soft start cycle, or
when the soft start pin is pulled to ground. Given the
typical soft start current of 8µA and a soft start timing
capacitor CSS, the start-up delay time to full available
average current will be:
tSS = (1.5)(105)(CSS)
Boost Supply
The VBOOST supply is bootstrapped via an external capaci-
tor. This supply provides gate drive to the topside switch
FET. The bootstrap capacitor is charged from 12VIN through
a diode when the switch node is pulled low.
The diode reverse breakdown voltage must be greater than
VIN + 12VIN. The bootstrap capacitor should be at least 100
times greater than the total input capacitance of the
topside FET. A capacitor in the range of 0.1µF to 1µF is
generally adequate for most applications.
Shutdown Function — Input Undervoltage Detect and
Threshold Hysteresis
The LT1339 RUN/SHDN pin uses a bandgap generated
reference threshold of about 1.25V. This precision thresh-
old allows use of the RUN/SHDN pin for both logic-level
shutdown applications and analog monitoring applica-
tions such as power supply sequencing.
Because an LT1339 controlled converter is a power trans-
fer device, a voltage that is lower than expected on the
input supply could require currents that exceed the sourc-
ing capabilities of that supply, causing the system to lock
up in an undervoltage state. Input supply start-up protec-
tion can be achieved by enabling the RUN/SHDN pin using
a resistor divider from the input supply to ground. Setting
the divider output to 1.25V when that supply is almost fully
enabled prevents the LT1339 regulator from drawing large
currents until the input supply is able to provide the
required power.
If additional hysteresis is desired for the enable function,
an external feedback resistor can be used from the LT1339
regulator output. If connection to the regulator output is
not desired, the 5VREF internal supply pin can be used.
Figure 3 shows a resistor connection on a 48V to 5V
converter that yields a 40V VIN start-up threshold for
regulator enable and also provides about 10% input
referred hysteresis.
VIN
48V
300k
390k
10k
OPTION 1
VOUT
5V
OPTION 2
2 5VREF
LT1339
13
RUN/SHDN
1339 • F03
Figure 3. Input Supply Sequencing Programming
The shutdown function can be disabled by connecting the
RUN/SHDN pin to the 12VIN rail. This pin is internally
clamped to 2.5V through a 20k series input resistance and
will therefore draw about 0.5mA when tied directly to 12V.
This additional current can be minimized by making the
connection through an external resistor (100k is typically
used).
Inductor Selection
The inductor for an LT1339 converter is selected based on
output power, operating frequency and efficiency require-
ments. Generally, the selection of inductor value can be
reduced to desired maximum ripple current in the inductor
(∆I). For a buck converter, the minimum inductor value for
a desired maximum operating ripple current can be deter-
mined using the following relation:
11
11 Page | ||
| Páginas | Total 20 Páginas | |
| PDF Descargar | [ Datasheet LT1339.PDF ] | |
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