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PDF LTC1438XCG Data sheet ( Hoja de datos )
| Número de pieza | LTC1438XCG | |
| Descripción | Dual High Efficiency/ Low Noise/ Synchronous Step-Down Switching Regulators | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LTC1438/LTC1439
Dual High Efficiency,
Low Noise, Synchronous
Step-Down Switching Regulators
FEATURES
DESCRIPTION
s Maintains Constant Frequency at Low Output Currents The LTC ®1438/LTC1439 are dual, synchronous step-
s Dual N-Channel MOSFET Synchronous Drive
down switching regulator controllers which drive external
s Programmable Fixed Frequency (PLL Lockable)
N-channel power MOSFETs in a phase-lockable fixed
s Wide VIN Range: 3.5V to 36V Operation
s Ultrahigh Efficiency
frequency architecture. The Adaptive PowerTM output stage
selectively drives two N-channel MOSFETs at frequencies
s Very Low Dropout Operation: 99% Duty Cycle
up to 400kHz while reducing switching losses to maintain
s Low Dropout, 0.5A Linear Regulator for VPP
high efficiencies at low output currents.
Generation or Low Noise Audio Supply
s Built-In Power-On Reset Timer
s Programmable Soft Start
s Low-Battery Detector
s Remote Output Voltage Sense
s Foldback Current Limiting (Optional)
An auxiliary 0.5A linear regulator using an external PNP
pass device provides a low noise, low dropout voltage
source. A secondary winding feedback control pin (SFB1)
guarantees regulation regardless of load on the main
output by forcing continuous operation.
s Pin Selectable Output Voltage
An additional comparator is available for use as a low
s Logic-Controlled Micropower Shutdown: IQ < 30µA
s Output Voltages from 1.19V to 9V
s Available in 28- and 36-Lead SSOP Packages
battery detector. A power-on reset timer (POR) is included
which generates a signal delayed by 65536/fCLK (typ
300ms) after the output is within 5% of the regulated
U
APPLICATIONS
output voltage. Internal resistive dividers provide pin
selectable output voltages with remote sense capability on
one of the two outputs.
s Notebook and Palmtop Computers, PDAs
s Portable Instruments
s Battery-Operated Devices
s DC Power Distribution Systems
The operating current levels are user-programmable via
external current sense resistors. Wide input supply range
allows operation from 3.5V to 30V (36V maximum).
, LTC and LT are registered trademarks of Linear Technology Corporation.
Adaptive Power is a trademark of Linear Technology Corporation.
TYPICAL APPLICATION
DB1, CMDSH-3
DB2, CMDSH-3 + 4.7µF
16V
BOOST 1
VPROG1
VIN
INTVCC
BOOST 2
M1 TGL1
TGL2
L1
10µH
D1
MBR140T3
VOUT1
5V
3.5A
RSENSE1
0.03Ω
+ COUT1
220µF
10V
M3*
CB1
0.1µF
M2
1000pF
CC1
1000pF
CC1A
220pF
TGS1
SW1
BG1
SENSE+ 1
LTC1439
SENSE– 1
ITH1
RUN/SS1
CDSC VPROG2
RC1
CSS1
COSC
10k
0.1µF
56pF
SGND
TGS2
SW2
BG2
SENSE+ 2
SENSE– 2
VOSENSE2
ITH2
PGND RUN/SS2
CSS2
0.1µF
CB2, 0.1µF
M6*
M5
1000pF
CC2
1000pF
RC2 CC2A
10k 470pF
M1, M2, M4, M5: Si4412DY M3, M6: IRLML2803 *NOT REQUIRED FOR LTC1438 BOLD LINES INDICATE HIGH CURRENT PATHS
+
M4
L2
10µH
CIN
22µF
35V
×4
VIN
5.2V TO 28V
D2
MBR140T3
RSENSE2
0.03Ω
+
1438 F01
VOUT2
3.3V
3.5A
COUT
220µF
10V
Figure 1. High Efficiency Dual 5V/3V Step-Down Converter
1
1 page  
TYPICAL PERFORMANCE CHARACTERISTICS
LTC1438/LTC1439
Efficiency vs Input Voltage
VOUT = 3.3V
100
VOUT = 3.3V
95
ILOAD = 1A
90
85
ILOAD = 100mA
80
75
70
0
5 10 15 20 25 30
INPUT VOLTAGE (V)
1438 G01
VIN – VOUT Dropout Voltage
vs Load Current
0.5
RSENSE = 0.033Ω
VOUT DROP OF 5%
0.4 M1, M2: Si4412
0.3
0.2
0.1
0
0 0.5 1.0 1.5 2.0 2.5 3.0
LOAD CURRENT (A)
1438 G04
Input Supply Current
vs Input Voltage
2.5
35
30
2.0
SHUTDOWN
CURRENT
25
1.5 20
1.0
0.5
0
0
15
5V AND
3.3V ON
5V OFF
3.3V ON
10
5V ON
3.3V OFF
5 10 15 20
INPUT VOLTAGE (V)
5
0
25 30
1438 G07
Burst Mode is a trademark of Linear Technology Corporation.
Efficiency vs Input Voltage
VOUT = 5V
100
VOUT = 5V
95
ILOAD = 1A
90
ILOAD = 100mA
85
80
75
70
0
5 10 15 20 25 30
INPUT VOLTAGE (V)
1438 G02
Load Regulation
0
– 0.25
RSENSE = 0.033Ω
– 0.50
– 0.75
–1.00
–1.25
–1.50
0
0.5 1.0 1.5 2.0 2.5 3.0
LOAD CURRENT (A)
1438 G05
INTVCC Regulation
vs INTVCC Load Current
2
EXTVCC = 0V
1
70°C
0
25°C
–1
–2
0
10 20 30 40 50
INTVCC LOAD CURRENT (mA)
1438 G08
Efficiency vs Load Current
100
VIN = 10V
95 VOUT = 5V
90 RSENSE = 0.33Ω
85
80
75
70
CONTINUOUS
MODE
Burst Mode®
OPERATION
65
Adaptive Power
60 MODE
55
50
0.001
0.01 0.1
1
LOAD CURRENT (A)
10
1435 G03
VITH Pin Voltage vs Output Current
3.0
2.5
2.0
1.5
Burst Mode
OPERATION
1.0
CONTINUOUS/Adaptive
Power MODE
0.5
0
0 10 20 30 40 50 60 70 80 90 100
OUTPUT CURRENT (%)
1438 G06
EXTVCC Switch Drop
vs INTVCC Load Current
300
70°C
200
25°C
– 45°C
100
0
0 5 10 15 20 25 30
INTVCC LOAD CURRENT (mA)
1438 G09
5
5 Page 
U
OPERATION (Refer to Functional Diagram)
Frequency Synchronization
A Phase-Locked Loop (PLL) is available on the LTC1439
to allow the oscillator to be synchronized to an external
source connected to the PLLIN pin. The output of the
phase detector at the PLL LPF pin is also the control input
of the oscillator, which operates over a 0V to 2.4V range
corresponding to – 30% to 30% in frequency. When
locked, the PLL aligns the turn-on of the top MOSFET to
the rising edge of the synchronizing signal. When PLLIN
is left open, PLL LPF goes low, forcing the oscillator to
minimum frequency.
LTC1438/LTC1439
the AUXDR pin is above 9.5V to allow regulated 12V
VPP supplies to be easily implemented. When AUXDR is
below 8.5V an external feedback divider may be used to set
other output voltages. Taking the AUXON pin low shuts
down the auxiliary regulator providing a convenient logic-
controlled power supply.
The AUX block can be used as a comparator having its
inverting input tied to the internal 1.19V reference. The
AUXDR pin is used as the output and requires an external
pull-up to a supply of less than 8.5V in order to inhibit the
invoking of the internal resistive divider.
Power-On Reset
The POR2 pin is an open drain output which pulls low
when the main regulator output voltage of the second
controller is out of regulation. When the output voltage
rises to within 7.5% of regulation, a timer is started which
releases POR2 after 216 (65536) oscillator cycles. This
function is not available on the LTC1438X.
Auxiliary Linear Regulator
The auxiliary linear regulator in the LTC1439 controls an
external PNP transistor for operation up to 500mA. A
precise internal AUXFB resistive divider is invoked when
INTVCC / EXTVCC Power
Power for the top and bottom MOSFET drivers and most
of the other LTC1438/LTC1439 circuitry is derived from
the INTVCC pin. The bottom MOSFET driver supply is also
connected to INTVCC. When the EXTVCC pin is left open, an
internal 5V low dropout regulator supplies INTVCC power.
If EXTVCC is taken above 4.8V, the 5V regulator is turned
off and an internal switch is turned on to connect EXTVCC
to INTVCC. This allows the INTVCC power to be derived
from a high efficiency external source such as the output
of the regulator itself or a secondary winding, as described
in the Applications Information section.
11
11 Page | ||
| Páginas | Total 32 Páginas | |
| PDF Descargar | [ Datasheet LTC1438XCG.PDF ] | |
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