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PDF LTC3828 Data sheet ( Hoja de datos )
| Número de pieza | LTC3828 | |
| Descripción | Dual 2-Phase Step-Down Controller | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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FEATURES
www■.daDtasuhaele,t41u8.c0o°mPhased Controllers Reduce Required
Input Capacitance and Power Supply Induced Noise
■ Tracking for Both Outputs
■ Constant Frequency Current Mode Control
■ Wide VIN Range: 4.5V to 28V Operation
■ Power Good Output Voltage Indicator
■ Adjustable Soft-Start Current Ramping
■ Foldback Output Current Limiting–
Disabled at Start-Up
■ No Reverse Current During Soft-Start Interval
■ Clock Output for 3-, 4-, 6-Phase Operation
■ Dual N-Channel MOSFET Synchronous Drive
■ ±1% Output Voltage Accuracy
■ Phase-Lockable Fixed Frequency 260kHz to 550kHz
■ OPTI-LOOP® Compensation Minimizes COUT
■ Very Low Dropout Operation: 99% Duty Cycle
■ Output Overvoltage Protection
■ Small 28-Lead SSOP and 5mm × 5mm QFN
Packages
U
APPLICATIO S
■ Telecom Infrastructure
■ ASIC Power Supply
■ Industry Equipment
LTC3828
Dual, 2-Phase Step-Down
Controller with Tracking
DESCRIPTIO
The LTC®3828 is a dual high performance step-down
switching regulator controller that drives all N-channel
synchronous power MOSFET stages. A constant fre-
quency current mode architecture allows for a phase-
lockable frequency of up to 550kHz. The TRCKSS pin
provides both soft-start and tracking functions. Multiple
LTC3828s can be daisy-chained in applications requiring
more than two voltages to be tracked.
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 a wide 4.5V to 28V
(30V maximum) input supply range, encompassing all bat-
tery chemistries.
The RUN pins control their respective channels indepen-
dently. The FCB/PLLIN pin selects among Burst Mode®
operation, skip-cycle mode and continuous current mode.
Current foldback limits MOSFET dissipation during short-
circuit conditions. Reverse current and current foldback
functions are disabled during soft-start.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode and OPTI-LOOP are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
Protected by U.S. Patents including 5481178, 5705919, 5929620, 6144194, 6177787,
6304066, 6580258
TYPICAL APPLICATIO
High Efficiency Dual 2.5V/3.3V Step-Down Converter with Tracking
+
4.7µF
VIN PGOOD INTVCC
TG1 TG2
1µF
CERAMIC
4.5V TO 28V
22µF
50V
CERAMIC
3.2µH
0.1µF
BOOST1
BOOST2
SW1
LTC3828
BG1
SW2
BG2
0.1µF
3.2µH
500kHz FCB/PLLIN
PGND
SENSE1+
SENSE2+
0.01Ω
1000pF
1000pF
SENSE1–
SENSE2–
3.3V
5A
+
63.4k 1%
47µF
4V
SP
63.4k 1%
20k
1% 20k
1%
0.1µF
220pF
VOSENSE1
TRCKSS2
ITH1
VOSENSE2
TRCKSS1
ITH2
RUN1 SGND RUN2
220pF
15k 15k
0.01Ω
TRCKSS1
20k
1%
0.1µF
42.5k
1%
56µF
4V
SP
2.5V
5A
+
3828 TA01
3828f
1
1 page  
LTC3828
TYPICAL PERFOR A CE CHARACTERISTICS TA = 25°C unless otherwise noted.
Oscillator Frequency vs
Temperature
www.da7t0a0sheet4u.com
600 VPLLFLTR = 2.4V
500
VPLLFLTR = 1.2V
400
300 VPLLFLTR = 0V
200
100
0
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
3828 G07
Maximum Current Sense
Threshold vs Temperature
80
VOUT = 5V
78
76
74
72
TRCKSS Current vs Temperature
1.5
1.3
1.1
0.9
0.7
0.5
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
3828 G08
INTVCC Voltage vs Temperature
5.1
5.0
Current Sense Pin Input Current vs
Temperature
37
35
33
31
29
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
3828 G09
Load Regulation
0
– 0.1
FCB = 0V
VIN = 15V
FIGURE 14
4.9 – 0.2
4.8 – 0.3
70
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
3828 G10
Maximum Current Sense
Threshold vs Duty Factor
75
50
25
0
0
20 40
60
80 100
DUTY FACTOR (%)
3828 G13
4.7
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
3828 G11
Maximum Current Sense
Threshold vs Percent of Nominal
Output Voltage (Foldback)
80
70
60
50
40
30
20
10
0
0 0.25 0.5 0.75 1.0
PERCENT ON NOMINAL OUTPUT VOLTAGE (%)
3828 G14
– 0.4
0
1 2 34
LOAD CURRENT (A)
5
3828 G12
Maximum Current Sense
Threshold vs Sense Common
Mode Voltage
80
75
70
65
60
01 2 345
COMM0N MODE VOLTAGE (V)
3828 G15
3828f
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5 Page 
U
OPERATIO (Refer to Functional Diagram)
Frequency Synchronization
The phase-locked loop allows the internal oscillator to be
wwws.dyantacshhreoent4iuz.ecdomto an external source via the FCB/PLLIN pin.
The output of the phase detector at the PLLFLTR pin is also
the DC frequency control input of the oscillator that
operates over a 260kHz to 550kHz range corresponding to
a DC voltage input from 0V to 2.4V. When locked, the PLL
aligns the turn on of the top MOSFET to the rising edge of
the synchronizing signal.
The internal master oscillator runs at a frequency twelve
times that of each controller’s frequency. The PHSMD pin
(UH package only) determines the relative phases be-
tween the internal controllers as well as the CLKOUT signal
as shown in Table 2. The phases tabulated are relative to
zero phase being defined as the rising edge of the top gate
(TG1) driver output of controller 1.
Table 2.
VPHSMD
Controller 1
Controller 2
CLKOUT
GND
0°
180°
60°
OPEN
0°
180°
90°
INTVCC
0°
240°
120°
The CLKOUT signal can be used to synchronize additional
power stages in a multiphase power supply solution
feeding a single, high current output or separate outputs.
Input capacitance ESR requirements and efficiency losses
are substantially reduced because the peak current drawn
from the input capacitor is effectively divided by the
number of phases used and power loss is proportional to
the RMS current squared. A two stage, single output
voltage implementation can reduce input path power loss
by 75% and radically reduce the required RMS current
rating of the input capacitor(s).
In the G28 package, CLKOUT is 90° out of phase with
channel 1 and channel 2.
Constant Frequency Operation
When the FCB/PLLIN pin is tied to INTVCC, Burst Mode
operation is disabled and the forced minimum output
current requirement is removed. This provides constant
frequency, discontinuous current (preventing reverse
LTC3828
inductor current) operation over the widest possible out-
put current range. This constant frequency operation is
not as efficient as Burst Mode operation, but does provide
a lower noise, constant frequency operating mode down
to approximately 1% of the designed maximum output
current.
Continuous Current (PWM) Operation
Tying the FCB/PLLIN pin to ground will force continuous
current operation. This is the least efficient operating
mode, but may be desirable in certain applications. The
output can source or sink current in this mode. When
sinking current while in forced continuous operation,
current will be forced back into the main power supply
potentially boosting the input supply to dangerous voltage
levels—BEWARE!
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.
Power Good (PGOOD) Pin
The PGOOD pin is connected to an open drain of an internal
MOSFET. The MOSFET turns on and pulls the pin low when
either output is not within ±7.5% of the nominal output
level as determined by the resistive feedback divider.
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
5.5V.
Foldback Current
Foldback current limiting is activated when the output
voltage falls below 70% of its nominal level. If a short is
present, a safe, low output current is provided due to
internal current foldback and actual power wasted is low
due to the efficient nature of the current mode switching
regulator. This function is disabled at start-up.
3828f
11
11 Page | ||
| Páginas | Total 30 Páginas | |
| PDF Descargar | [ Datasheet LTC3828.PDF ] | |
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