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PDF LTC1267CG-ADJ5 Data sheet ( Hoja de datos )
| Número de pieza | LTC1267CG-ADJ5 | |
| Descripción | Dual High Efficiency Synchronous Step-Down Switching Regulators | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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FEATURES
s Dual Outputs: 3.3V and 5V, Two Adjustables or
Adjustable and 5V
s Wide VIN Range: 4V to 40V
s Ultra-High Efficiency: Up to 95%
s Low Supply Current in Shutdown: 20µA
s Current Mode Operation for Excellent Line and Load
Transient Response
s High Efficiency Maintained Over a Wide Output
Current Range
s Independent Micropower Shutdown
s Very Low Dropout Operation: 100% Duty Cycle
s Synchronous FET Switching for High Efficiency
s Available in Standard 28-Pin SSOP
APPLICATI S
s Notebook and Palmtop Computers
s Battery-Operated Digital Devices
s Portable Instruments
s DC Power Distribution Systems
LTC1267
LTC1267-ADJ/LTC1267-ADJ5
Dual High Efficiency
Synchronous Step-Down
Switching Regulators
DESCRIPTIO
The LTC®1267 series are dual synchronous step-down
switching regulator controllers featuring automatic Burst
ModeTM operation to maintain high efficiencies at low
output currents. The LTC1267 is composed of two sepa-
rate regulator blocks, each driving a pair of external comple-
mentary power MOSFETs at switching frequencies up to
400kHz. The LTC1267 uses a constant off-time current-
mode architecture to provide constant ripple current in the
inductor and provide excellent line and load transient
response.
A separate pin and on-board switch allow the MOSFET
driver power to be derived from the regulated output
voltage, providing significant efficiency improvement when
operating at high input voltage. The output current level is
user-programmable via an external current sense resistor.
The LTC1267 series is ideal for applications requiring dual
output voltages with high conversion efficiencies over a
wide load current range in a small amount of board space.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a trademark of Linear Technology Corporation.
TYPICAL APPLICATI
VIN
5.4V to 25V
VOUT3
3.3V
2A
+ CIN3
100µF
50V
RSENSE3
0.05Ω
+
3.3µF
P-CH
Si9435DY
L3
20µH
D3
MBRS140T3
+ COUT3
220µF
10V
×2
1N4148
0.15µF
8 31
0.1µF
1000pF
4 VCC3 CAP3
PGATE 3
5
PDRIVE 3
14 SENSE+ 3
VCC
13 SENSE– 3
12
SHDN3
6
NGATE 3
N-CH
Si9410DY
PGND3 SGND3 CT3
7 11 9
0.15µF
2
27 26
28 21
VIN MSHDN
LTC1267
CAP5
EXT VCC VCC5
25
PGATE 5
PDRIVE 5 24
SENSE+ 5 18
SENSE– 5 17
19
SHDN5
NGATE 5 23
ITH3 ITH5 CT5 SGND5 PGND5
10 15 16 20 22
CT3 CC3 CC5 CT5
270pF 3300pF 3300pF 270pF
1N4148
+
P-CH
Si9435DY
0.1µF
L5
33µH
3.3µF
RSENSE5
0.05Ω
1000pF
N-CH
Si9410DY
D5
MBRS140T3
+
RSENSE3: KRL SL-1R050J
L3: COILTRONICS CTX20-4
RC3 RC5
1k 1k
RSENSE5: KRL SL-1R050J
L5: COILTRONICS CTX33-4
+ CIN5
100µF
50V
VOUT5
5V
2A
COUT5
220µF
10V
×2
SHDN3, SHDN5, MSHDN
0V = NORMAL, >2V = SHDN
LTC1267 • F01
Figure 1. High Efficiency Dual 3.3V, 5V
1
1 page  
LTC1267
LTC1267-ADJ/LTC1267-ADJ5
TYPICAL PERFORMANCE CHARACTERISTICS
5V Output Efficiency
vs Line Voltage
100
95
LOGIC THRESHOLD
GATE, 1A
90
NOTE 6
85
LOGIC
80 THRESHOLD
GATE, 0.1A
75 STANDARD
THRESHOLD GATE, 1A
70 VEXTVCC = 9V
STANDARD
65 THRESHOLD GATE, 0.1A
VEXTVCC = 9V
60
0 5 10 15 20 25 30 35 40
INPUT VOLTAGE (V)
LTC1267 • G04
Operating Frequency
vs (VIN – VOUT)
2.0
VOUT = 5V
ILOAD = 700mA
1.5
0°C
25°C
70°C
1.0
0.5
0
0 5 10 15 20 25
(VIN – VOUT) VOLTAGE (V)
LTC1267 • G07
3.3V Output Efficiency
vs Line Voltage
100
95 LOGIC THRESHOLD
GATE, 1A
90
NOTE 6
85
80
LOGIC
THRESHOLD
75 GATE, 0.1A
STANDARD
70 THRESHOLD GATE, 1A
VEXTVCC = 9V
STANDARD
65 THRESHOLD GATE, 0.1A
VEXTVCC = 9V
60
0 5 10 15 20 25 30 35
INPUT VOLTAGE (V)
40
LTC1267 • G05
Off-Time vs Output Voltage
160
140
120
100
80
60
3.3V OUTPUT REGULATOR
40
5V OUTPUT REGULATOR
20
0
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
OUTPUT VOLTAGE (V)
LTC1267 • F08
Line Regulation
60
40
NOTE 6
20
0
– 20
– 40
–60
0
5 10 15 20 25 30 35 40
INPUT VOLTAGE (V)
LT1267 • G06
Current Sense Threshold Voltage
180
160
140 MAXIMUM THRESHOLD
120
100
80
60
40 MINIMUM THRESHOLD
20
0
0 10 20 30 40 50 60 70 80 90 100
TEMPERATURE (°C)
LTC1267 • G09
PI FU CTIO S (Applies to both regulator sections)
VIN: Main Supply Input Pin.
EXT VCC: External VCC Supply for the Regulators. See EXT
VCC Pin Connection.
VCC: Output of the Internal 4.5V Linear Regulator, EXT VCC
Switch, and Supply Inputs for Driver and Control Circuits.
The driver and control circuits are powered from the
higher of the 4.5V regulator or EXT VCC voltage. Must be
closely decoupled to the power ground.
PGND: Power Ground. Connect to the source of N-channel
MOSFET and the (–) terminal of CIN.
SGND: Small-Signal Ground. Must be routed separately
from other grounds to the (–) terminal of COUT.
PGATE: Level Shifted Gate Drive for the Top P-channel
MOSFET. The voltage swing at the PGate pin is from VIN to
(VIN – VCC).
PDRIVE: High Current Gate Drive for the Top P-channel
MOSFET. The PDrive pin swings from VCC to GND.
NGATE: High Current Drive for the Bottom N-channel
MOSFET. The NGate pin swings from GND to VCC.
5
5 Page 
UU W U
APPLICATIO S I FOR ATIO
the voltage comparator. This causes Burst Mode opera-
tion to be activated when the LTC1267 would normally be
in continuous operation. The effect is most pronounced
with low values of RSENSE and can be improved by oper-
ating at higher frequencies with lower values of L. The
output remains in regulation at all times.
EXT VCC Pin Connection
The LTC1267 contains an internal PNP switch connected
between the EXT VCC and VCC pins. The switch closes and
supplies the VCC power whenever the EXT VCC pin is higher
in voltage than the 4.5V internal regulator. This allows the
MOSFET driver and control power to be derived from the
output during normal operation and from the internal
regulator when the output is out of regulation (start-up,
short circuit).
Significant efficiency gain can be realized by powering VCC
from the output, since the VIN current resulting from the
driver and control currents will be scaled by a factor of
Duty Cycle/Efficiency. For LTC1267, LTC1267-ADJ or
LTC1267-ADJ5 this simply means connecting the EXT
VCC pin directly to VOUT of the 5V regulator.
The following list summarizes the four possible connec-
tions for EXT VCC:
1. EXT VCC left open. This will cause VCC to be powered
only from the internal 4.5V regulator, resulting in re-
duced MOSFET gate drive levels and an efficiency
penalty of up to 10% at high input voltages.
2. EXT VCC connected directly to highest VOUT of the two
regulators. This is the normal connection for LTC1267/
LTC1267-ADJ/LTC1267-ADJ5 and provides the high-
est efficiency.
3. EXT VCC connected to an output-derived boost net-
work. For 3.3V and other low voltage regulators, effi-
ciency gains can still be realized by connecting EXT VCC
to an output-derived voltage which has been boosted to
greater than 4.5V. This can be done either with the
inductive boost winding shown in Figure 5a or the
capacitive charge pump shown in Figure 5b. The charge
pump has the advantage of simple magnetics and
generally provides the highest efficiency at the expense
of a slightly higher parts count.
LTC1267
LTC1267-ADJ/LTC1267-ADJ5
EXT VCC VIN
PGATE 3
PDRIVE 3
LTC1267
NGATE 3
VIN
+
CIN
P-CH
1N4148
L
1:1 •
•
RSENSE
N-CH
PGND3
LTC1267 • F05A
Figure 5a. Inductive Boost Circuit for EXT VCC
+
1µF
VOUT
3.3V
+
COUT
EXT VCC VIN
PGATE 3
PDRIVE 3
LTC1267
NGATE 3
PGND3
VIN
+
CIN BAT 85
+
1µF BAT 85
0.22µF
P-CH
N-CH
VN2222LL
L RSENSE
BAT 85
VOUT
3.3V
+
COUT
LTC1267 • F05B
Figure 5b. Capacitive Charge Pump for EXT VCC
4. EXT VCC connected to an external supply. If an external
supply is available in the 5V to 10V range it may be used
to power EXT VCC providing it is compatible with the
MOSFET gate drive requirements. When driving stan-
dard threshold MOSFETs, the external supply must
always be present during operation to prevent MOSFET
failure due to insufficient gate drive.
Under the condition that EXT VCC is connected to VOUT1
which is greater than 5.5V, to power down the whole
regulator, both the pins MSHDN and SHDN1 have to be
pulled high. If SHDN1 is left floating or grounded the
EXT VCC may self-power from VOUT1, preventing com-
plete shutdown.
LTC1267 Adjustable Applications
When an output voltage other than 3.3V or 5V is required,
the LTC1267-ADJ and LTC1267-ADJ5 adjustable ver-
sions are used with an external resistive divider from VOUT
to the VFB1, 2 pins. This is shown in Figure 6. The regulated
voltage is determined by:
) )VOUT =
1 + R2
R1
1.25V
11
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LTC1267CG-ADJ5.PDF ] | |
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