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PDF LTC1628I Data sheet ( Hoja de datos )
| Número de pieza | LTC1628I | |
| Descripción | High Efficiency/ 2-Phase Synchronous Step-Down Switching Regulators | |
| Fabricantes | Linear Technology | |
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Hay una vista previa y un enlace de descarga de LTC1628I (archivo pdf) en la parte inferior de esta página. Total 32 Páginas | ||
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LTC1628/LTC1628-PG
High Efficiency, 2-Phase
Synchronous Step-Down Switching Regulators
FEATURES
s Out-of-Phase Controllers Reduce Required Input
Capacitance and Power Supply Induced Noise
s OPTI-LOOPTM Compensation Minimizes COUT
s Dual N-Channel MOSFET Synchronous Drive
s ±1% Output Voltage Accuracy
s Power Good Output Voltage Monitor (LTC1628-PG)
s DC Programmed Fixed Frequency 150kHz to 300kHz
s Wide VIN Range: 3.5V to 36V Operation
s Very Low Dropout Operation: 99% Duty Cycle
s Adjustable Soft-Start Current Ramping
s Foldback Output Current Limiting
s Latched Short-Circuit Shutdown with Defeat Option
s Output Overvoltage Protection
s Remote Output Voltage Sense
s Low Shutdown IQ: 20µA
s 5V and 3.3V Standby Regulators
s Small 28-Lead SSOP Package
s Selectable Constant Frequency or Burst ModeTM
Operation
U
APPLICATIO S
s Notebook and Palmtop Computers, PDAs
s Battery Chargers
s Portable Instruments
s Battery-Operated Digital Devices
s DC Power Distribution Systems
DESCRIPTIO
The LTC®1628/LTC1628-PG are high performance dual
step-down switching regulator controllers that drive all
N-channel synchronous power MOSFET stages. A con-
stant frequency current mode architecture allows adjust-
ment of the frequency up to 300kHz. Power loss and noise
due to the ESR of the input capacitors are minimized by
operating the two controller output stages out of phase.
OPTI-LOOP compensation allows the transient response
to be optimized over a wide range of output capacitance and
ESR values. The precision 0.8V reference and power good
output indicator are compatible with future microproces-
sor generations, and a wide 3.5V to 30V (36V maximum)
input supply range encompasses all battery chemistries.
A RUN/SS pin for each controller provides both soft-start
and optional timed, short-circuit shutdown. Current
foldback limits MOSFET dissipation during short-circuit
conditions when overcurrent latchoff is disabled. Output
overvoltage protection circuitry latches on the bottom
MOSFET until VOUT returns to normal. The FCB mode pin
can select among Burst Mode, constant frequency mode
and continuous inductor current mode or regulate a
secondary winding. The LTC1628-PG includes a power
good output pin that replaces the FLTCPL, fault coupling
control pin of the LTC1628.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode and OPTI-LOOP are trademarks of Linear Technology Corporation.
TYPICAL APPLICATIO
L1
6.3µH
D1
VOUT1
5V
5A
RSENSE1
0.01Ω
+
COUT1
47µF
6V
SP
R2
105k
1%
M1
M2
R1
20k
1%
+
4.7µF
CB1, 0.1µF
D3
VIN
TG1
INTVCC
TG2
BOOST1
BOOST2
SW1 SW2
LTC1628
BG1 BG2
1000pF
CC1
220pF
RC1
15k
SGND
SENSE1+
PGND
SENSE2+
SENSE1–
VOSENSE1
ITH1
RUN/SS1
CSS1
0.1µF
SENSE2–
VOSENSE2
ITH2
RUN/SS2
CSS2
0.1µF
1µF
D4 CERAMIC
CB2, 0.1µF
M3
M4
1000pF
CC2
220pF
RC2
15k
R3
20k
1%
VIN
CIN 5.2V TO 28V
22µF
50V
CERAMIC
L2
6.3µH
D2
R4
63.4k
1%
RSENSE2
0.01Ω
VOUT2
3.3V
5A
COUT
56µF
6V
SP
+
M1, M2, M3, M4: FDS6680A
Figure 1. High Efficiency Dual 5V/3.3V Step-Down Converter
1628 F01
1
1 page  
LTC1628/LTC1628-PG
TYPICAL PERFOR A CE CHARACTERISTICS
Internal 5V LDO Line Reg
5.1
ILOAD = 1mA
5.0
4.9
4.8
4.7
4.6
4.5
4.4
0
5 10 15 20 25 30 35
INPUT VOLTAGE (V)
1628 G07
Maximum Current Sense Threshold
vs VRUN/SS (Soft-Start)
80
VSENSE(CM) = 1.6V
60
40
20
0
01
2 34
VRUN/SS (V)
56
1628 G10
Load Regulation
0.0
–0.1
FCB = 0V
VIN = 15V
FIGURE 1
–0.2
–0.3
–0.4
0
1 2 34
LOAD CURRENT (A)
5
1628 G13
Maximum Current Sense Threshold
vs Duty Factor
75
50
25
0
0 20 40 60 80 100
DUTY FACTOR (%)
1628 G08
Maximum Current Sense Threshold
vs Sense Common Mode Voltage
80
76
72
68
64
60
0
1 2 34
COMMON MODE VOLTAGE (V)
5
1628 G11
VITH vs VRUN/SS
2.5
VOSENSE = 0.7V
2.0
1.5
1.0
0.5
0
012 34
VRUN/SS (V)
56
1628 G14
Maximum Current Sense Threshold
vs Percent of Nominal Output
Voltage (Foldback)
80
70
60
50
40
30
20
10
0
0 25 50 75 100
PERCENT ON NOMINAL OUTPUT VOLTAGE (%)
1628 G09
Current Sense Threshold
vs ITH Voltage
90
80
70
60
50
40
30
20
10
0
–10
–20
–30
0 0.5 1 1.5 2 2.5
VITH (V)
1628 G12
SENSE Pins Total Source Current
100
50
0
–50
–100
0
246
VSENSE COMMON MODE VOLTAGE (V)
1628 G15
5
5 Page 
U
OPERATIO (Refer to Functional Diagram)
Frequency Setting
The FREQSET pin provides frequency adjustment of the
internal oscillator from approximately 140kHz to 310kHz.
This input is nominally biased through an internal resistor
to the 1.19V reference, setting the oscillator frequency to
approximately 220kHz. This pin can be driven from an
external AC or DC signal source to control the instanta-
neous frequency of the oscillator.
INTVCC/EXTVCC Power
Power for the top and bottom MOSFET drivers and most
other internal circuitry is derived from the INTVCC pin.
When the EXTVCC pin is left open, an internal 5V low
dropout linear regulator supplies INTVCC power. If EXTVCC
is taken above 4.7V, the 5V regulator is turned off and an
internal switch is turned on connecting EXTVCC to INTVCC.
This allows the INTVCC power to be derived from a high
efficiency external source such as the output of the regu-
lator itself or a secondary winding, as described in the
Applications Information.
Standby Mode Pin
The STBYMD pin is a three-state input that controls
common circuitry within the IC as follows: When the
STBYMD pin is held at ground, both controller RUN/SS
pins are pulled to ground providing a single control pin to
shut down both controllers. When the pin is left open, the
internal RUN/SS currents are enabled to charge the
RUN/SS capacitor(s), allowing the turn-on of either con-
troller and activating necessary common internal biasing.
When the STBYMD pin is taken above 2V, both internal
linear regulators are turned on independent of the state on
the RUN/SS pins of the two switching regulator control-
lers, providing an output power source for “wake-up”
circuitry. Decouple the pin with a small capacitor (0.01µF)
to ground if the pin is not connected to a DC potential.
Output Overvoltage Protection
An overvoltage comparator, OV, guards against transient
overshoots (>7.5%) as well as other more serious condi-
tions that may overvoltage the output. In this case, the top
MOSFET is turned off and the bottom MOSFET is turned on
until the overvoltage condition is cleared.
LTC1628/LTC1628-PG
Fault Coupling Pin
The FLTCPL pin (LTC1628 only) controls two functions
that can operate individually (FLTCPL = 0V) or unilaterally
(FLTCPL = INTVCC) between the two controllers. When the
FLTCPL pin is grounded (internally tied default mode for
the LTC1628-PG), 1) the FCB input forces continuous
operation only on the first controller when the applied
voltage drops below 0.8V and 2) the short-circuit latchoff
function only latches off the controller having the shorted
output. When the FLTCPL pin is tied to INTVCC, 1) the FCB
input forces continuous operation on both controllers
when the applied voltage drops below 0.8V and 2) the
short-circuit latchoff function latches off both controllers
when either has a shorted output.
Power Good (PGOOD) Pin
The PGOOD pin (LTC1628-PG only) is connected to an
open drain of an internal MOSFET. The MOSFET turns on
and pulls the pin low when both the outputs are not within
±7.5% of their nominal output levels as determined by
their resistive feedback dividers. When both outputs meet
the ±7.5% requirement, the MOSFET is turned off within
10µs and the pin is allowed to be pulled up by an external
resistor to a source of up to 7V.
Foldback Current, Short-Circuit Detection
and Short-Circuit Latchoff
The RUN/SS capacitors are used initially to limit the inrush
current of each switching regulator. After the controller
has been started and been given adequate time to charge
up the output capacitors and provide full load current, the
RUN/SS capacitor is used in a short-circuit time-out
circuit. If the output voltage falls to less than 70% of its
nominal output voltage, the RUN/SS capacitor begins
discharging on the assumption that the output is in an
overcurrent and/or short-circuit condition. If the condition
lasts for a long enough period as determined by the size of
the RUN/SS capacitor, the controller (or both controllers
as determined by the FLTCPL pin, LTC1628 only) will be
shut down until the RUN/SS pin(s) voltage(s) are recycled.
This built-in latchoff can be overridden by providing a
>5µA pull-up at a compliance of 5V to the RUN/SS pin(s).
This current shortens the soft start period but also pre-
vents net discharge of the RUN/SS capacitor(s) during an
11
11 Page | ||
| Páginas | Total 32 Páginas | |
| PDF Descargar | [ Datasheet LTC1628I.PDF ] | |
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