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PDF LTC3419 Data sheet ( Hoja de datos )
| Número de pieza | LTC3419 | |
| Descripción | Dual Monolithic 600mA Synchronous Step-Down Regulator | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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FEATURES
■ High Efficiency Dual Step-Down Outputs: Up to 96%
■ 600mA Current per Channel at VIN = 3V
■ Only 35μA Quiescent Current During Operation
(Both Channels)
■ 2.25MHz Constant-Frequency Operation
■ 2.5V to 5.5V Input Voltage Range
■ Low Dropout Operation: 100% Duty Cycle
■ No Schottky Diodes Required
■ Internally Compensated for All Ceramic Capacitors
■ Independent Internal Soft-Start for Each Channel
■ Available in Fixed Output Versions
■ Current Mode Operation for Excellent Line and Load
Transient Response
■ 0.6V Reference Allows Low Output Voltages
■ User-Selectable Burst Mode® Operation
■ Short-Circuit Protected
■ Ultralow Shutdown Current: IQ < 1μA
■ Available in Small MSOP or 3mm × 3mm
DFN-8 Packages
APPLICATIONS
■ Cellular Telephones
■ Digital Still Cameras
■ Wireless and DSL Modems
■ Portable Media Players
■ PDAs/Palmtop PCs
LTC3419www.DataSheet4U.com
Dual Monolithic 600mA
Synchronous Step-Down
Regulator
DESCRIPTION
The LTC®3419 is a dual, 2.25MHz, constant-frequency,
synchronous step-down DC/DC converter in a tiny
3mm × 3mm DFN package. 100% duty cycle provides
low dropout operation, extending battery life in portable
systems. Low output voltages are supported with the 0.6V
feedback reference voltage. Each regulator can supply
600mA output current.
The input voltage range is 2.5V to 5.5V, making it ideal
for Li-Ion and USB powered applications. Supply cur-
rent during operation is only 35μA and drops to <1μA in
shutdown. A user-selectable mode input allows the user
to trade off between high efficiency Burst Mode operation
and pulse-skipping mode.
An internally set 2.25MHz switching frequency allows the
use of tiny surface mount inductors and capacitors. Inter-
nal soft-start reduces inrush current during start-up. Both
outputs are internally compensated to work with ceramic
output capacitors. The LTC3419 is available in a low profile
(0.75mm) 3mm × 3mm DFN package. The LTC3419 is also
available in a fixed output voltage configuration selected
via internal resistor dividers (see Table 2).
, LT, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
Burst Mode is a registered trademark 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.
TYPICAL APPLICATION
Dual Monolithic Buck Regulator in 8-Lead 3 × 3 DFN
VIN
2.5V TO 5.5V
10μF
VOUT2
1.8V AT
600mA
3.3μH
22pF
RUN2 VIN RUN1
MODE
LTC3419
SW2 SW1
3.3μH
22pF
VOUT1
2.5V AT
600mA
10μF 118k
VFB2
VFB1
GND
59k
59k 187k
10μF
3419 TA01
Efficiency and Power Loss vs
Output Current
100 VIN = 3.6V
90
10
80 1
70
60 0.1
50
40 0.01
30
20
10
0
0.1
VOUT = 1.2V
VOUT = 1.8V
VOUT = 2.5V
0.001
0.0001
1 10 100 1000
OUTPUT CURRENT (mA)
3419 TA01b
3419f
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LTC3419www.DataSheet4U.com
TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, VIN = 3.6V, unless otherwise noted.
Efficiency vs Load Current
100
90
80
70
60
50
40
30
20
10
0 VOUT = 1.2V
0.1 1
VIN = 2.7V
VIN = 3.6V
VIN = 4.2V
10 100 1000
OUTPUT CURRENT (mA)
3419 G10
Efficiency vs Load Current
100
90
80
70
60
50
40
30
20
10
0 VOUT = 1.8V
0.1 1
VIN = 2.7V
VIN = 3.6V
VIN = 4.2V
10 100 1000
OUTPUT CURRENT (mA)
3419 G11
Efficiency vs Load Current
100
90
80
70
60
50
40
30
20
10
0 VOUT = 2.5V
0.1 1
VIN = 2.7V
VIN = 3.6V
VIN = 4.2V
10 100 1000
OUTPUT CURRENT (mA)
3419 G12
Efficiency vs Load Current
100
Burst Mode OPERATION
90
80
70
PULSE SKIP MODE
60
50
40
30
20
10
0 VOUT = 1.8V
0.1 1
10 100
OUTPUT CURRENT (mA)
1000
3419 G13
Load Regulation
3.0
2.5
2.0
VOUT = 1.2V
VOUT = 1.8V
VOUT = 2.5V
1.5
Burst Mode OPERATION
1.0
0.5
0
–0.5
–1.0
0
100 200 300 400 500 600
LOAD CURRENT (mA)
3419 G14
Load Regulation
2.0
VOUT = 1.8V
1.5
1.0
0.5
0
–0.5
–1.0
0
Burst Mode OPERATION
PULSE SKIP MODE
100 200 300 400 500 600
LOAD CURRENT (mA)
3419 G15
Line Regulation
0.6
VOUT = 1.8V
ILOAD = 100mA
0.4
Start-Up from Shutdown
RUN
2V/DIV
0.2
VOUT
1V/DIV
0
–0.2
IL
500mA/DIV
–0.4
–0.6
2.5 3.0 3.5 4.0 4.5 5.0 5.5
VIN (V)
3419 G16
VIN = 3.6V
VOUT = 1.8V
ILOAD = 0A
250μs/DIV
Start-Up from Shutdown
RUN
2V/DIV
VOUT
1V/DIV
ILOAD
500mA/DIV
3419 G17
VIN = 3.6V
VOUT = 1.8V
RLOAD = 3Ω
250μs/DIV
3419 G18
3419f
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LTC3419www.DataSheet4U.com
APPLICATIONS INFORMATION
Checking Transient Response
The regulator loop response can be checked by looking
at the load transient response. Switching regulators take
several cycles to respond to a step in load current. When
a load step occurs, VOUT immediately shifts by an amount
equal to ΔILOAD • ESR, where ESR is the effective series
resistance of COUT. ΔILOAD also begins to charge or dis-
charge COUT generating a feedback error signal used by the
regulator to return VOUT to its steady-state value. During
this recovery time, VOUT can be monitored for overshoot
or ringing that would indicate a stability problem.
The initial output voltage step may not be within the
bandwidth of the feedback loop, so the standard second
order overshoot/DC ratio cannot be used to determine the
phase margin. In addition, feedback capacitors (CF1 and
CF2) can be added to improve the high frequency response,
as shown in Figure 1. Capacitor CF provides phase lead by
creating a high frequency zero with R2 which improves
the phase margin.
The output voltage settling behavior is related to the stability
of the closed-loop system and will demonstrate the actual
overall supply performance. For a detailed explanation of
optimizing the compensation components, including a re-
view of control loop theory, refer to Application Note 76.
In some applications, a more severe transient can be caused
by switching in loads with large (>1μF) input capacitors.
The discharged input capacitors are effectively put in paral-
lel with COUT, causing a rapid drop in VOUT. No regulator
can deliver enough current to prevent this problem if the
switch connecting the load has low resistance and is driven
quickly. The solution is to limit the turn-on speed of the
load switch driver. A Hot Swap™ controller is designed
specifically for this purpose and usually incorporates cur-
rent limiting, short-circuit protection, and soft-starting.
Efficiency Considerations
The percent efficiency of a switching regulator is equal to
the output power divided by the input power times 100%.
It is often useful to analyze individual losses to determine
what is limiting the efficiency and which change would
produce the most improvement. Percent efficiency can
be expressed as:
% Efficiency = 100% – (L1 + L2 + L3 + ...)
where L1, L2, etc., are the individual losses as a percent-
age of input power.
Although all dissipative elements in the circuit produce
losses, four sources usually account for the losses in
LTC3419 circuits: 1) VIN quiescent current, 2) switching
losses, 3) I2R losses, 4) other system losses.
1. The VIN current is the DC supply current given in the
Electrical Characteristics which excludes MOSFET
driver and control currents. VIN current results in a
small (<0.1%) loss that increases with VIN, even at
no load.
2. The switching current is the sum of the MOSFET driver
and control currents. The MOSFET driver current re-
sults from switching the gate capacitance of the power
MOSFETs. Each time a MOSFET gate is switched from
low to high to low again, a packet of charge dQ moves
from VIN to ground. The resulting dQ/dt is a current out
of VIN that is typically much larger than the DC bias cur-
rent. In continuous mode, IGATECHG = fO(QT + QB), where
QT and QB are the gate charges of the internal top and
bottom MOSFET switches. The gate charge losses are
proportional to VIN and thus their effects will be more
pronounced at higher supply voltages.
3. I2R losses are calculated from the DC resistances
of the internal switches, RSW, and external inductor,
RL. In continuous mode, the average output current
flows through inductor L, but is “chopped” between
the internal top and bottom switches. Thus, the series
resistance looking into the SW pin is a function of both
top and bottom MOSFET RDS(ON) and the duty cycle
(DC) as follows:
RSW = (RDS(ON)TOP) • (DC) + (RDS(ON)BOT) • (1– DC)
Hot Swap is a trademark of Linear Technology Corporation.
3419f
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11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LTC3419.PDF ] | |
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