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PDF LTC3417A-2 Data sheet ( Hoja de datos )
| Número de pieza | LTC3417A-2 | |
| Descripción | Dual Synchronous 1.5A/1A 4MHz Step-Down DC/DC Regulator | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LTC3417A-2www.DataSheet4U.com
Dual Synchronous
1.5A/1A 4MHz
Step-Down DC/DC Regulator
FEATURES
n High Efficiency: Up to 95%
n 1.5A/1A Guaranteed Minimum Output Current
n Synchronizable to External Clock
n No Schottky Diodes Required
n Programmable Frequency Operation: 1.5MHz or
Adjustable From 0.6MHz to 4MHz
n Low Ripple (<35mVP-P) BurstMode® Operation
IQ: 125μA in Sleep
n Low RDS(ON) Internal Switches
n Short-Circuit Protected
n VIN: 2.25V to 5.5V
n Current Mode Operation for Excellent Line and Load
Transient Response
n Ultralow Shutdown Current: IQ < 1μA
n Low Dropout Operation: 100% Duty Cycle
n Power Good Ouput
n Phase Pin Selects 2nd Channel Phase Relationship
with Respect to 1st Channel
n Internal Soft-Start with Individual Run Pin Control
n Available in Small Thermally Enhanced
(5mm × 3mm) DFN and 20-Lead TSSOP Packages
APPLICATIONS
n GPS/Navigation Systems
n Automotive Instrumentation
n PC Cards
n Industrial Power Supplies
n General Purpose Point of Load DC/DC
DESCRIPTION
The LTC®3417A-2 is a dual constant frequency, synchro-
nous step-down DC/DC converter. Intended for medium
power applications, it operates from a 2.25V to 5.5V input
voltage range and has a constant programmable switching
frequency, allowing the use of tiny, low cost capacitors
and inductors 2mm or less in height. Each output voltage
is adjustable from 0.8V to 5V. Internal synchronous, low
RDS(ON) power switches provide high efficiency without
the need for external Schottky diodes.
A user selectable mode input allows the user to trade
off ripple voltage for light load efficiency. Burst Mode
operation provides high efficiency at light loads, while
Pulse Skip mode provides low ripple noise at light loads.
A phase mode pin allows the second channel to operate
in-phase or 180° out-of-phase with respect to channel 1.
Out-of-phase operation produces lower RMS current on
VIN and thus lower stress on the input capacitor.
To further maximize battery life, the P-channel MOSFETs
are turned on continuously in dropout (100% duty cycle)
and both channels draw a total quiescent current of only
100μA. In shutdown, the device draws <1μA.
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, 6580258, 6304066, 6127815, 6498466, 6611131, 6144194.
TYPICAL APPLICATION
VIN
2.5V TO 5.5V
VOUT1
1.8V
1.5A
47μF
10μF
1.5μH
22pF
VIN
511k
412k
5.9k
2200pF
VIN
FREQ
SW1 SW2
RUN1
RUN2
LTC3417A-2
VFB1
VFB2
ITH1 ITH2
GND
2.2μH
22pF
VIN
866k
412k
2.87k
6800pF
3417A-2 TA01
VOUT2
2.5V
1A
22μF
VOUT2 Efficiency
(Burst Mode Operation)
100 REFER TO FIGURE 4
10
95 EFFICIENCY
1
90
0.1
85
0.01
80 POWER LOSS
75
70
0.001
0.001
VIN = 3.6V
VOUT = 2.5V
FREQ = 1MHz 0.0001
0.01 0.1
1
LOAD CURRENT (A)
3417A-2 TA01a
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TYPICAL PERFORMANCE CHARACTERISTICS
LTC3417A-2www.DataSheet4U.com
OUT1 Efficiency vs Load Current
100 VIN = 2.5V
95 VOUT = 1.8V
90
85
80
75
70
65
60
0.001
Burst Mode
OPERATION
PULSE SKIP
FORCED
CONTINUOUS
REFER TO FIGURE 4
0.01 0.1 1 10
LOAD CURRENT (A)
3417A-2 G07
OUT2 Efficiency vs Load Current
100
VIN = 3.6V
95 VOUT = 2.5V
90
85
80
75
70
65
60
0.001
Burst Mode
OPERATION
PULSE SKIP
FORCED
CONTINUOUS
REFER TO FIGURE 4
0.01 0.1
1
LOAD CURRENT (A)
3417A-2 G08
OUT1 Efficiency vs VIN
(Burst Mode Operation)
100 VOUT = 1.8V
95
ILOAD = 460mA
90
ILOAD = 1.4A
85
80
75
REFER TO FIGURE 4
70
2 2.5 3 3.5 4 4.5 5 5.5
VIN (V)
3417A-2 G09
OUT2 Efficiency vs VIN
(Pulse Skipping Mode)
100
ILOAD = 250mA
95
90 ILOAD = 800mA
Load Step OUT1
VOUT1
100mV/DIV
Load Step OUT2
VOUT2
100mV/DIV
85
IOUT1
IOUT2
500mA/DIV
500mA/DIV
80
75
VOUT = 2.5V
REFER TO FIGURE 4
70
2 2.5 3 3.5 4 4.5 5 5.5
VIN (V)
3417A-2 G10
VIN = 3.6V
100μs/DIV
VOUT = 1.8V
ILOAD = 0.25A to 1.4A
REFER TO FIGURE 4
3417A-2 G11
VIN = 3.6V
100μs/DIV
VOUT = 2.5V
ILOAD = 0.25A to 0.8A
REFER TO FIGURE 4
3417A-2 G12
Efficiency vs Frequency OUT1
94
TA = 27°C
VIN = 3.6V
92 VOUT = 1.8V
IOUT = 300mA
90
88
86
84
82
0
1234
FREQUENCY (MHz)
5
3417A-2 G13
Efficiency vs Frequency OUT2
90
85
80
75
70
65
60
0
TA = 27°C
VIN = 3.6V
VOUT = 2.5V
IOUT = 100mA
1 2 34
FREQUENCY (MHz)
3417A-2 G14
RDS(ON) vs VIN OUT1
0.105
0.100
0.095
P-CHANNEL SWITCH
TA = 27°C
0.090
0.085
N-CHANNEL SWITCH
0.080
2 2.5 3 3.5 4
VIN (V)
4.5 5 5.5
3417A-2 G15
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LTC3417A-2www.DataSheet4U.com
APPLICATIONS INFORMATION
When D1 = D2 then the equation simplifies to:
( )IRMS = I1 +I2 D(1– D)
or
( ) ( )IRMS = I1 +I2
VOUT VIN – VOUT
VIN
where the maximum average output currents I1 and I2
equal the respective peak currents minus half the peak-
to-peak ripple currents:
I1
= ILIM1
–
ΔIL1
2
I2
=
ILIM2
–
ΔIL2
2
These formula have a maximum at VIN = 2VOUT, where
IRMS = (I1 + I2)/2. This simple worst case is commonly
used to determine the highest IRMS.
For “out of phase” operation, the ripple current can be
lower than the “in phase” current.
In the “out of phase” case, the maximum IRMS does not
occur when VOUT1 = VOUT2. The maximum typically oc-
curs when VOUT1 – VIN/2 = VOUT2 or when VOUT2 – VIN/2
= VOUT1. As a good rule of thumb, the amount of worst
case ripple is about 75% of the worst case ripple in the
“in phase” mode. Also note that when VOUT1 = VOUT2 =
VIN/2 and I1 = I2, the ripple is zero.
Note that capacitor manufacturer’s ripple current ratings
are often based on only 2000 hours lifetime. This makes
it advisable to further derate the capacitor, or choose a
capacitor rated at a higher temperature than required.
Several capacitors may also be paralleled to meet the
size or height requirements of the design. An additional
0.1μF to 1μF ceramic capacitor is also recommended on
VIN for high frequency decoupling, when not using an all
ceramic capacitor solution.
Output Capacitor (COUT1 and COUT2) Selection
The selection of COUT1 and COUT2 is driven by the required
ESR to minimize voltage ripple and load step transients.
Typically, once the ESR requirement is satisfied, the
capacitance is adequate for filtering. The output ripple
(ΔVOUT) is determined by:
VOUT
IL
ESRCOUT
+
8
•
fO
1
• COUT
where fO = operating frequency, COUT = output capacitance
and ΔIL = ripple current in the inductor. The output ripple
is highest at maximum input voltage, since ΔIL increases
with input voltage. With ΔIL = 0.35ILOAD(MAX), the output
ripple will be less than 100mV at maximum VIN and fO =
1MHz with:
ESRCOUT < 150mΩ
Once the ESR requirements for COUT have been met, the
RMS current rating generally far exceeds the IRIPPLE(P-P)
requirement, except for an all ceramic solution.
In surface mount applications, multiple capacitors may
have to be paralleled to meet the capacitance, ESR or RMS
current handling requirement of the application. Aluminum
electrolytic, special polymer, ceramic and dry tantalum
capacitors are all available in surface mount packages.
The OS-CON semiconductor dielectric capacitor avail-
able from Sanyo has the lowest ESR(size) product of any
aluminum electrolytic at a somewhat higher price. Special
polymer capacitors, such as Sanyo POSCAP, offer very
low ESR, but have a lower capacitance density than other
types. Tantalum capacitors have the highest capacitance
density, but it has a larger ESR and it is critical that the
capacitors are surge tested for use in switching power
supplies. An excellent choice is the AVX TPS series of
surface tantalums, available in case heights ranging from
2mm to 4mm. Aluminum electrolytic capacitors have a
significantly larger ESR, and are often used in extremely
cost-sensitive applications provided that consideration
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| PDF Descargar | [ Datasheet LTC3417A-2.PDF ] | |
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