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PDF LTC1539 Data sheet ( Hoja de datos )
| Número de pieza | LTC1539 | |
| Descripción | Dual High Efficiency/ Low Noise/ Synchronous Step-Down Switching Regulators | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de LTC1539 (archivo pdf) en la parte inferior de esta página. Total 32 Páginas | ||
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LTC1538-AUX/LTC1539
Dual High Efficiency,
Low Noise, Synchronous
Step-Down Switching Regulators
FEATURES
DESCRIPTION
s Maintains Constant Frequency at Low Output Currents
s Dual N-Channel MOSFET Synchronous Drive
s Programmable Fixed Frequency (PLL Lockable)
s Wide VIN Range: 3.5V to 36V Operation
s Ultrahigh Efficiency
s Very Low Dropout Operation: 99% Duty Cycle
s Low Dropout, 0.5A Linear Regulator for VPP
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)
s Pin Selectable Output Voltage
s 5V Standby Regulator Active in Shutdown: IQ < 200µA
s Output Voltages from 1.19V to 9V
s Available in 28- and 36-Lead SSOP Packages
U
APPLICATIONS
s Notebook and Palmtop Computers, PDAs
s Portable Instruments
s Battery-Operated Devices
s DC Power Distribution Systems
The LTC ®1538-AUX/LTC1539 are dual, synchronous step-
down switching regulator controllers which drive external
N-channel power MOSFETs in a phase-lockable fixed
frequency architecture. The Adaptive PowerTM output stage
selectively drives two N-channel MOSFETs at frequencies
up to 400kHz while reducing switching losses to maintain
high efficiencies at low output currents.
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.
A 5V/20mA regulator, internal 1.19V reference and an
uncommitted comparator remain active when both con-
trollers are shut down. A power-on reset timer (POR) is
included which generates a signal delayed by 65536/fCLK
(typ 300ms) after the controller’s output is within 5% of
the regulated first voltage. Internal resistive dividers pro-
vide pin selectable output voltages with remote sense
capability on one of the two outputs.
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
5V STANDBY
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
LTC1539
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 LTC1538-AUX BOLD LINES INDICATE HIGH CURRENT PATHS
VIN
+ CIN 5.2V TO 28V
22µF
35V
×4
M4
L2
10µH
D2
MBR140T3
RSENSE2
0.03Ω
+
1538 F01
VOUT2
3.3V
3.5A
COUT
220µF
10V
Figure 1. High Efficiency Dual 5V/3V Step-Down Converter
1
1 page  
LTC1538-AUX/LTC1539
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency vs Input Voltage:
VOUT = 3.3V
100
VOUT = 3.3V
95
ILOAD = 1A
90
85
ILOAD = 100mA
80
Efficiency vs Input Voltage:
VOUT = 5V
100
VOUT = 5V
95
ILOAD = 1A
90
ILOAD = 100mA
85
80
75 75
70
0
5 10 15 20 25 30
INPUT VOLTAGE (V)
1538/39 • G01
VIN – VOUT Dropout Voltage vs
Load Current
0.5
RSENSE = 0.033Ω
VOUT DROP OF 5%
0.4
0.3
0.2
0.1
70
0
5 10 15 20 25 30
INPUT VOLTAGE (V)
1538/39 • G02
Load Regulation
0
– 0.25
RSENSE = 0.033Ω
– 0.50
– 0.75
–1.00
–1.25
0
0 0.5 1.0 1.5 2.0 2.5 3.0
LOAD CURRENT (A)
1538/39 • G04
–1.50
0
0.5 1.0 1.5 2.0 2.5 3.0
LOAD CURRENT (A)
1538/39 • G05
Input Supply Current
vs Input Voltage
2.5
INTVCC Regulation
vs INTVCC Load Current
100 2
EXTVCC = 0V
2.0 80
5V, 3.3V OFF
5V STANDBY
1.5 60
1.0 5V, 3.3V ON
40
1
0
70°C
25°C
5V OFF, 3.3V ON
–1
0.5 20
5V ON, 3.3V OFF
00
0 5 10 15 20 25 30
INPUT VOLTAGE (V)
–2
0
LTC1538/39 • TPC07
Adaptive Power and Burst Mode are trademarks of Linear Technology Corporation.
10 20 30 40 50
INTVCC LOAD CURRENT (mA)
1538/39 • G08
Efficiency vs Load Current
100
VIN = 10V
95 VOUT = 5V
90 RSENSE = 0.33Ω
85
80
75
70
CONTINUOUS
MODE
Burst ModeTM
OPERATION
65
Adaptive PowerTM
60 MODE
55
50
0.001
0.01 0.1
1
LOAD CURRENT (A)
10
1538/39 • G03
VITH Pin Voltage vs Output Current
3.0
2.5
2.0
1.5
Burst Mode
OPERATION
1.0
0.5
CONTINUOUS/
Adaptive Power
MODE
0
0 10 20 30 40 50 60 70 80 90 100
OUTPUT CURRENT (%)
1538/39 • 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)
1538/39 • G09
5
5 Page 
U
OPERATION (Refer to Functional Diagram)
Frequency Synchronization
A Phase-Locked Loop (PLL) is available on the LTC1539
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.
Power-On Reset
The POR1 pin is an open drain output which pulls low
when the main regulator output voltage of the LTC1539
first controller is out of regulation. When the output
voltage rises to within 5% of regulation, a timer is started
which releases POR1 after 216 (65536) oscillator cycles.
Auxiliary Linear Regulator
The auxiliary linear regulator in the LTC1538-AUX and
LTC1539 controls an external PNP transistor for operation
up to 500mA. A precise internal AUXFB resistive divider is
invoked when 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 provid-
ing a convenient logic-controlled power supply.
LTC1538-AUX/LTC1539
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.
INTVCC / EXTVCC Power
Power for the top and bottom MOSFET drivers and most
of the other LTC1538-AUX/LTC1539 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.
The 5V/20mA INTVCC regulator can be used as a standby
regulator when the two controllers are in shutdown or
when either or both controllers are on. Irrespective of the
signals on the RUN/SS pins, the INTVCC pin will follow the
voltage applied to the EXTVCC pin when the voltage applied
to the EXTVCC pin is taken above 4.8V. The externally
applied voltage is required to be less than the voltage
applied to the VIN pin at all times, even when both control-
lers are shut down. This prevents a voltage backfeed
situation from the source applied to the EXTVCC pin to the
VIN pin. If the EXTVCC pin is tied to the first controller’s 5V
output, the nominal INTVCC pin voltage will stay in the
guaranteed range of 4.7V to 5.2V.
APPLICATIONS INFORMATION
The basic LTC1539 application circuit is shown in Fig-
ure 1. External component selection is driven by the load
requirement and begins with the selection of RSENSE. Once
RSENSE is known, COSC and L can be chosen. Next, the
power MOSFETs and D1 are selected. Finally, CIN and COUT
are selected. The circuit shown in Figure 1 can be config-
ured for operation up to an input voltage of 28V (limited by
the external MOSFETs).
RSENSE Selection for Output Current
RSENSE is chosen based on the required output current.
The LTC1538-AUX/LTC1539 current comparator has a
maximum threshold of 150mV/RSENSE and an input com-
mon mode range of SGND to INTVCC. The current com-
parator threshold sets the peak of the inductor current,
yielding a maximum average output current IMAX equal to
the peak value less half the peak-to-peak ripple current, ∆IL.
11
11 Page | ||
| Páginas | Total 32 Páginas | |
| PDF Descargar | [ Datasheet LTC1539.PDF ] | |
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