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PDF LTC7812 Data sheet ( Hoja de datos )
| Número de pieza | LTC7812 | |
| Descripción | 38V Synchronous Boost+Buck Controller | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LTC7812
Low IQ, 38V Synchronous
Boost+Buck Controller
Features
n Synchronous Boost and Buck Controllers
n When Cascaded, Allows VIN Above, Below or Equal
to Regulated VOUT
n Output Remains in Regulation Through Input Dips
(e.g., Cold Crank) Down to 2.5V
n Wide Bias Input Voltage Range: 4.5V to 38V
n Low Input and Output Ripple
n Low EMI
n Fast Output Transient Response
n High Light Load Efficiency
n Low Operating IQ: 33µA (Both Channels On)
n Low Operating IQ: 28µA (Buck Channel On)
n RSENSE or Lossless DCR Current Sensing
n Buck Output Voltage Range: 0.8V ≤ VOUT ≤ 24V
n Boost Output Voltage Up to 60V
n Phase-Lockable Frequency (75kHz to 850kHz)
n Small 32-Pin 5mm × 5mm QFN Package
Applications
n Automotive and Industrial Power Systems
n High Power Battery Operated Systems
Description
The LTC®7812 is a high performance synchronous
Boost+Buck DC/DC switching regulator controller that
drives all N-channel power MOSFET stages. It contains
independent step-up (boost) and step-down (buck) control-
lers that can regulate two separate outputs or be cascaded
to regulate an output voltage from an input voltage that
can be above, below or equal to the output voltage. The
LTC7812 operates from a wide 4.5V to 38V input supply
range. When biased from the output of the boost regulator,
the LTC7812 can operate from an input supply as low as
2.5V after start-up. The 33μA no-load quiescent current
extends operating run time in battery-powered systems.
Unlike conventional buck-boost regulators, the LTC7812’s
cascaded Boost+Buck solution has continuous, non-
pulsating, input and output currents, substantially reducing
voltage ripple and EMI. The LTC7812 has independent
feedback and compensation points for the boost and buck
regulation loops, enabling a fast output transient response
that can be easily optimized externally.
L, LT, LTC, LTM, Burst Mode, OPTI-LOOP and µModule are registered trademarks and
No RSENSE is a trademark of Linear Technology Corporation. All other trademarks are the
property of their respective owners.
Typical Application
VIN
5V TO 38V
DOWN TO
2.5V AFTER
START-UP
+ 33µF
6.8µF
2mΩ
Wide Input Range to 12V/8A Low IQ, Cascaded Boost+Buck Regulator
1µH
VMID, 14V**
4.7µH
3mΩ
6.8µF + 33µF 499k
499k
22µF + 47µF
VOUT
12V
8A*
46.4k
35.7k
0.1µF
4.7µF
0.1µF
SENSE2+ SENSE2– BG2 SW2 BOOST2 TG2
INTVCC
PGND VFB2 VBIAS TG1 BOOST1 SW1 BG1 SENSE1+ SENSE1– VFB1
LTC7812
EXTVCC
RUN1 RUN2 ITH1
ITH2 TRACK/SS1 SS2 FREQ PLLIN/MODE SGND
15k
100pF
4.7nF
1.86k
820pF
6.8nF
0.1µF
0.01µF
* WHEN VIN < 8V, MAXIMUM LOAD CURRENT AVAILABLE IS REDUCED
** VMID = 14V WHEN VIN < 14V
VMID FOLLOWS VIN WHEN VIN > 14V
7812 TA01a
For more information www.linear.com/LTC7812
7812fa
1
1 page  
LTC7812
E lectrical Characteristics The l denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at TA = 25°C. VBIAS = 12V, VRUN1,2 = 5V, EXTVCC = 0V unless otherwise
noted. (Note 2)
SYMBOL
PARAMETER
High Fixed Frequency
Synchronizable Frequency
PGOOD1 Output
PGOOD1 Voltage Low
PGOOD1 Leakage Current
PGOOD1 Trip Level
Delay For Reporting a Fault
OV2 Boost Overvoltage Indicator Output
OV2 Voltage Low
OV2 Leakage Current
OV2 Trip Level
BOOST2 Charge Pump
BOOST2 Charge Pump Available Output
Current
CONDITIONS
VFREQ = INTVCC; PLLIN/MODE = DC Voltage
PLLIN/MODE = External Clock
IPGOOD1 = 2mA
VPGOOD1 = 5V
VFB1 with Respect to Set Regulated Voltage
VFB1 Ramping Negative
Hysteresis
VFB1 Ramping Positive
Hysteresis
IOV2 = 2mA
VOV2 = 5V
VRFeBg2uRlaatemdpVinogltaPgoesitive with Respect to Set
Hysteresis
VBOOST2 = 16V; VSW2 = 12V;
Forced Continuous Mode
MIN
485
l 75
TYP MAX UNITS
535 585
kHz
850 kHz
0.2 0.4
±1
–13 –10 –7
2.5
7 10 13
2.5
40
V
µA
%
%
%
%
µs
0.2 0.4
±1
6 10 13
1.5
V
µA
%
%
65 µA
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: The LTC7812 is tested under pulsed load conditions such that
TJ ≈ TA. The LTC7812E is guaranteed to meet performance specifications
from 0°C to 85°C. Specifications over the –40°C to 125°C operating
junction temperature range are assured by design, characterization and
correlation with statistical process controls. The LTC7812I is guaranteed
over the –40°C to 125°C operating junction temperature range and the
LTC7812H is guaranteed over the –40°C to 150°C operating junction
temperature range. High junction temperatures degrade operating
lifetimes; operating lifetime is derated for junction temperatures greater
than 125°C. Note that the maximum ambient temperature consistent with
these specifications is determined by specific operating conditions in
conjunction with board layout, the rated package thermal impedance and
other environmental factors. TJ is calculated from the ambient temperature
TA and power dissipation PD according to the following formula: TJ = TA +
(PD • θJA), where θJA = 44°C/W.
Note 3: This IC includes overtemperature protection that is intended to
protect the device during momentary overload conditions. The maximum
rated junction temperature will be exceeded when this protection is active.
Continuous operation above the specified absolute maximum operating
junction temperature may impair device reliability or permanently damage
the device.
Note 4: The LTC7812 is tested in a feedback loop that servos VITH1,2 to
a specified voltage and measures the resultant VFB. The specification at
85°C is not tested in production and is assured by design, characterization
and correlation to production testing at other temperatures (125°C for
the LTC7812E/LTC7812I, 150°C for the LTC7812H). For the LTC7812I
and LTC7812H, the specification at 0°C is not tested in production and is
assured by design, characterization and correlation to production testing
at –40°C.
Note 5: Dynamic supply current is higher due to the gate charge being
delivered at the switching frequency. See the Applications Information
section.
Note 6: Rise and fall times are measured using 10% and 90% levels. Delay
times are measured using 50% levels.
Note 7: The minimum on-time condition is specified for an inductor
peak-to-peak ripple current ≥ 40% of IMAX (See the Minimum On-Time
Considerations in the Applications Information section).
Note 8: Do not apply a voltage or current source to these pins. They must
be connected to capacitive loads only, otherwise permanent damage may
occur.
For more information www.linear.com/LTC7812
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5 Page 
LTC7812
Pin Functions
SW1, SW2 (Pins 1, 30): Switch Node Connections to
Inductors.
TG1, TG2, (Pins 2, 29): High Current Gate Drives for Top
N-Channel MOSFETs. These are the outputs of floating
drivers with a voltage swing equal to INTVCC superimposed
on the switch node voltage SW.
PGOOD1 (Pin 3): Open-Drain Logic Output. PGOOD1 is
pulled to ground when the voltage on the VFB1 pin is not
within ±10% of its set point.
TRACK/SS1, SS2 (Pins 4,11): External Tracking and Soft-
Start Input. For the buck channel, the LTC7812 regulates
the VFB1 voltage to the smaller of 0.8V or the voltage on
the TRACK/SS1 pin. For the boost channel, the LTC7812
regulates the VFB2 voltage to the smaller of 1.2V or the
voltage on the SS2 pin. An internal 5µA pull-up current
source is connected to this pin. A capacitor to ground at
this pin sets the ramp time to final regulated output voltage.
Alternatively, a resistor divider on another voltage supply
connected to the TRACK/SS1 pin allow the LTC7812 buck
output to track another supply during start-up.
ITH1, ITH2 (Pins 5, 15): Error Amplifier Outputs and Switch-
ing Regulator Compensation Points. Each associated
channel’s current comparator trip point increases with
this control voltage.
VFB1, VFB2 (Pins 6, 14): Receives the remotely sensed
feedback voltage for each controller from an external
resistive divider across the output.
SENSE1+, SENSE2+ (Pins 7, 12): The (+) Input to the
cDoifnfetrroelnletidaloCffusrertesnbt eCtowmeepnartahteorSsE. NThSeE–ITaHnpdinSvEoNlStaEg+epainnds
FinorcothnejubnocotisotncwhaitnhnRelS,EtNhSeESsEeNt tShEe2c+uprrinenstutpripplitehsrecsuhrroelndt.
to the current comparator.
SENSE1–, SENSE2– (Pins 8, 13): The (–) Input to the Dif-
ferential Current Comparators. When SENSE1– is greater
than INTVCC, then SENSE1– pin supplies current to the
current comparator for the buck channel.
FREQ (Pin 9): The Frequency Control Pin for the Internal
VCO. Connecting the pin to GND forces the VCO to a fixed
low frequency of 350kHz. Connecting the pin to INTVCC
forces the VCO to a fixed high frequency of 535kHz.
Other frequencies between 50kHz and 900kHz can be
programmed using a resistor between FREQ and GND.
The resistor and an internal 20µA source current create a
voltage used by the internal oscillator to set the frequency.
PLLIN/MODE (Pin 10): External Synchronization Input to
Phase Detector and Forced Continuous Mode Input. When
an external clock is applied to this pin, the phase-locked
loop will force the rising TG1 and BG2 signals to be syn-
chronized with the rising edge of the external clock, and
the regulators operate in forced continuous mode. When
not synchronizing to an external clock, this input, which
acts on both controllers, determines how the LTC7812
operates at light loads. Pulling this pin to ground selects
Burst Mode operation. An internal 100k resistor to ground
also invokes Burst Mode operation when the pin is floated.
Tying this pin to INTVCC forces continuous inductor current
operation. Tying this pin to a voltage greater than 1.2V and
less than INTVCC – 1.3V selects pulse-skipping operation.
This can be done by connecting a 100k resistor from this
pin to INTVCC.
SGND (Pins 16, 18, 20, 21): Small Signal Ground com-
mon to both controllers. All four pins must be tied together
near the LTC7812 and must be routed separately from
high current grounds to the common (–) terminals of the
CIN capacitors.
RUN1, RUN2 (Pins 17, 19): Run Control Inputs for Each
Controller. Forcing RUN1 below 1.17V and RUN2 below
1.20V shuts down that controller. Forcing both of these
pins below 0.7V shuts down the entire LTC7812, reducing
quiescent current to approximately 10µA.
For more information www.linear.com/LTC7812
7812fa
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11 Page | ||
| Páginas | Total 30 Páginas | |
| PDF Descargar | [ Datasheet LTC7812.PDF ] | |
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