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PDF LTC3569 Data sheet ( Hoja de datos )
| Número de pieza | LTC3569 | |
| Descripción | Triple Buck Regulator | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LTC3569www.DataSheet4U.com
FEATURES
Triple Buck Regulator With
1.2A and Two 600mA Outputs and
Individual Programmable References
DESCRIPTION
n Three Independent Current Mode Buck DC/DC
Regulators (1.2A and 2x 600mA)
n Single Pin Programmable VFB Servo Voltages from
800mV Down to 425mV (in 25mV Steps)
n Pull VFB High to Make Each 600mA Buck a Slave for
Higher Current Operation
n Pulse Skip or Burst Mode® Operation
n Programmable Switching Frequency
(1MHz to 3MHz) or Fixed 2.25MHz
n Synchronizable (1.2MHz to 3MHz)
n VIN Range 2.5V to 5.5V
n All Regulators Internally Compensated
n PGOOD Output Flag
n Quiescent Current <100μA (All Regulators in Burst
Mode Operation)
n Zero Shutdown Current
n Overtemperature and Short-Circuit Protection
n Tiny 3mm × 3mm 20-Lead QFN and Thermally
Enhanced TSSOP FE-16 Packages
The LTC®3569 contains three monolithic, synchronous
step-down DC/DC converters. Intended for medium power
applications, it operates over a 2.5V to 5.5V input voltage
range. The operating frequency is adjustable from 1MHz
to 3MHz, allowing the use of tiny, low cost capacitors and
inductors. The three output voltages are independently
programmable by toggling the EN pins up to 15 times,
lowering the 800mV FB references by 25mV per cycle. The
first buck regulator sources load currents up to 1200mA.
The other two buck regulators each provide 600mA.
The two 600mA buck regulators can also be configured
to operate as slave power stages, running in parallel with
another internal buck regulator to supply higher load
currents. When operating as parallel, slave output stages,
discrete external components are shared and available
output currents sum together.
L, LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners. Protected by U.S. Patents
including 5481178, 6127815, 6304066, 6498466, 6580258, 6611131, 7170195.
APPLICATIONS
n Portable Applications with Multiple Supply Rails
n General Purpose Step-Down DC/DC
n Dynamic Voltage Scaling Applications
TYPICAL APPLICATION
VIN 2.2μH
22μF SVIN PVIN SW1
OUT1 = 2.5V
1200mA
20pF 510k
10μF
EN1 FB1
EN2
LTC3569
EN3
MODE
SW2
RT
FB2
2.5μH
240k
20pF 300k
OUT2 = 1.8V
600mA
4.7μF
PGOOD
240k
2.5μH
SW3
FB3
SGND PGND
20pF 150k
300k
OUT3 = 1.2V
600mA
4.7μF
3569 TA01a
Efficiency vs Load Current
100
VIN = 3V
90
80
70 VIN = 5V
60
50
40
30
20
10
0
0.01
0.1
BURST
PULSE SKIP
OUT1 = 2.5V
1 10 100
ILOAD (mA)
1000 10000
3569 TA01b
3569f
1
1 page  
LTC3569www.DataSheet4U.com
TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, unless otherwise noted.
Efficiency vs VSUPPLY
OUT1 = 1.8V
95
90
BUCK1 ONLY
85
80
75
70
65
2
ILOAD = 270mA
ILOAD = 220mA
ILOAD = 170mA
ILOAD = 120mA
34
VSUPPLY (V)
5
6
3569 G04
Efficiency vs VSUPPLY
OUT2 = 1.2V
95
90
BUCK2 ONLY
85
80
75
70
65
2
ILOAD = 210mA
ILOAD = 170mA
ILOAD = 110mA
ILOAD = 70mA
34
VSUPPLY (V)
5
6
3569 G05
Efficiency vs VSUPPLY
OUT3 = 1.5V
95
90
BUCK3 ONLY
85
80
75
70
65
2
ILOAD = 210mA
ILOAD = 170mA
ILOAD = 110mA
ILOAD = 70mA
34
VSUPPLY (V)
5
6
3569 G06
Oscillator Frequency
vs Temperature
2.40
VIN = 5.5V
2.30 VIN = 3.5V
2.20 VIN = 2.5V
2.10
VRT = SVIN
2.00
–50 0
50 100
TEMPERATURE (°C)
150
3569 G07
RDS(ON) SW1
vs VSUPPLY and Temperature
0.35
NSW1
100°C
PSW1
0.30
25°C
0.25
0.20
0.15 –50°C
0.10
2
345
VSUPPLY (V)
6
3569 G08
VFB vs Temperature
0.3
VREF SET TO MAX
0.2
0.1
0.0
–0.1
–0.2
–0.3
–50
0 50 100
TEMPERATURE (°C)
VFB1
VFB2
VFB3
150
3569 G10
ISVIN vs VSUPPLY Pulse Skip
700
600 ALL 3
500
2 BUCKS ENABLED
400
300 1 BUCK ENABLED
200
100
0
2
NO LOAD
345
VSUPPLY (V)
6
3569 G11
RDS(ON) SW2 and SW3
vs VSUPPLY and Temperature
0.50
100°C
0.45
NSW2 & 3
PSW3 & 3
0.40 25°C
0.35
0.30
0.25
–50°C
0.20
0.15
0.10
2
345
VSUPPLY (V)
6
3569 G09
ISVIN
vs VSUPPLY Burst Mode Operation
120
100 ALL 3
80 2 BUCKS ENABLED
60
1 BUCK ENABLED
40
20
0
2
NO LOAD
345
VSUPPLY (V)
6
3569 G12
3569f
5
5 Page 
LTC3569www.DataSheet4U.com
OPERATION
tor (NCOMP) signals to turn-off the N-channel switch, so
that is does not discharge the output capacitor. When a
rising clock edge occurs, the P-channel switch turns on
repeating the cycle.
The peak inductor current is controlled by the error amplifier
(EA) and is influenced by the slope compensation. The error
amplifier compares the FB pin voltage to the programmed
internal reference (REF). When the load current increases,
the FB voltage decreases. When the FB voltage falls below
the reference voltage, the error amplifier output rises
to increase the peak inductor current until the average
inductor current matches the new load current. With the
inductor current equal to the load current, the duty cycle
will stabilize to a value equal to VOUT/VIN.
Low Current Operation
At light loads, the FB voltage may rise above the refer-
ence voltage. If this occurs the error amplifier signals
the control loop to go to sleep, and the P-channel turns
off immediately. The inductor current then discharges
through the N-channel switch until the inductor current
approaches zero; whereupon the SW goes Hi-Z, and the
output capacitor supplies power to the load. When the
load discharges the output capacitor the feedback voltage
falls and the error amp wakes up the buck, restarting the
main control loop as if a clock cycle has just begun. This
sleep cycle helps minimize the switching losses which are
dominated by the gate charge losses of the power devices.
Two operating modes are available to control the operation
of the LTC3569 at low currents, Burst Mode operation and
pulse skip mode.
Select Burst Mode operation to optimize efficiency at low
output currents. In Burst Mode operation the inductor cur-
rent reaches a fixed current before the P-channel switch
compares inductor current against the value determined
by ITH. This burst clamp causes the output voltage to rise
above the regulation voltage and forces a longer sleep cycle.
This greatly reduces switching losses and average quiescent
current at light loads, at the cost of higher ripple voltage.
Pulse skip mode is intended for lower output voltage ripple
at light load currents. Here, the peak P-channel current is
compared with the value determined by the error amplifier
output. Then, the P-channel is turned off and the N-channel
switch is turned on until either the next cycle begins or the
N-channel comparator (NCOMP) turns off the N-channel
switch. If the NCOMP trips, the SW node goes Hi-Z and
the buck operates discontinuously. In pulse skip mode
the LTC3569 continues to switch at a constant frequency
down to very low currents; where it eventually begins
skipping pulses. Because the LTC3569 remains active at
lighter load currents in pulse skip mode, the efficiency
performance is traded off against output voltage ripple
and electromagnetic interference (EMI).
Dropout Operation
When the input supply voltage decreases towards the out-
put voltage the duty cycle automatically increases to 100%;
which is the dropout condition. In dropout, the P-channel
switch is turned on continuously with the output voltage
being equal to the input voltage minus the voltage drop
across the internal P-channel switch and the inductor.
Low Supply Operation
The LTC3569 incorporates an undervoltage lockout circuit
which shuts down the part when the input voltage drops
below 2.5V to prevent unstable operation. The UVLO
function does not reset the reference voltage DAC. (See
Programming the Reference.)
Slave Power Stage
When the FB pin of one of the two 600mA regulators is tied
to SVIN that regulator’s control circuits are disabled and
the regulator’s switch pin is configured to follow a master
regulator; either the first 600mA regulator (regulator 2) or
the 1.2A regulator (regulator 1). In this way, two regulator
power stages are ganged together (e.g. switch pins shorted
together to a single inductor) to support higher current
levels. This permits three permutations of power levels:
three independent regulators at 1.2A, 600mA and 600mA;
3569f
11
11 Page | ||
| Páginas | Total 24 Páginas | |
| PDF Descargar | [ Datasheet LTC3569.PDF ] | |
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