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PDF LTC3417A Data sheet ( Hoja de datos )
| Número de pieza | LTC3417A | |
| Descripción | Dual Synchronous 1.5A/1A 4MHz Step-Down DC/DC Regulator | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LTC3417Awww.DataSheet4U.com
Dual Synchronous
1.5A/1A 4MHz
Step-Down DC/DC Regulator
FEATURES
■ High Efficiency: Up to 95%
■ 1.5A/1A Guaranteed Minimum Output Current
■ Synchronizable to External Clock
■ No Schottky Diodes Required
■ Programmable Frequency Operation: 1.5MHz or
Adjustable From 0.6MHz to 4MHz
■ Low RDS(ON) Internal Switches
■ Short-Circuit Protected
■ VIN: 2.25V to 5.5V
■ Current Mode Operation for Excellent Line and Load
Transient Response
■ 125µA Quiescent Current in Sleep Mode
■ Ultralow Shutdown Current: IQ < 1µA
■ Low Dropout Operation: 100% Duty Cycle
■ Power Good Output
■ Phase Pin Selects 2nd Channel Phase Relationship
with Respect to 1st Channel
■ Internal Soft-Start with Individual Run Pin Control
■ Available in Small Thermally Enhanced
(5mm × 3mm) DFN and 20-Lead TSSOP Packages
U
APPLICATIO S
■ GPS/Navigation
■ Digital Cameras
■ PC Cards
■ Wireless and DSL Modems
■ General Purpose Point of Load DC/DC
DESCRIPTIO
The LTC®3417A 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 switch-
ing 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® opera-
tion 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 a lower RMS derating 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.
, 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, 6580258, 6304066, 6127815, 6498466,
6611131, 6144194
TYPICAL APPLICATIO
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
VFB1
VFB2
ITH1 ITH2
GND
2.2µH
VIN
22pF
866k
412k
2.87k
6800pF
3417 TA01
VOUT2
2.5V
1A
22µF
OUT2 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)
3417 TA01a
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LTC3417Awww.DataSheet4U.com
TYPICAL PERFOR
OUT2 Efficiency vs VIN
(Pulse Skipping Mode)
100
ILOAD = 250mA
95
90 ILOAD = 800mA
A CE CHARACTERISTICS
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)
3417 G10
VIN = 3.6V
100µs/DIV
VOUT = 1.8V
ILOAD = 0.25A to 1.4A
REFER TO FIGURE 4
3417 G11
VIN = 3.6V
100µs/DIV
VOUT = 2.5V
ILOAD = 0.25A to 0.8A
REFER TO FIGURE 4
3417 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
3417 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)
3417 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
3417 G15
RDS(ON) vs VIN OUT2
0.20
0.19
P-CHANNEL SWITCH
0.18
TA = 27°C
0.17
0.16
0.15
N-CHANNEL SWITCH
0.14
2 2.5 3 3.5 4 4.5 5 5.5
VIN (V)
3417 G16
Frequency vs VIN
6
4
2 FREQ = 143k TO GROUND
0
–2
–4
FREQ = VIN
–6
–8
–10
2 2.5 3 3.5 4 4.5 5 5.5
VIN (V)
3417 G17
Frequency vs Temperature
15
10 FREQ = VIN
5
0
FREQ = 143k TO GROUND
–5
–10
–15
–50 –25
0 25 50 75
TEMPERATURE (˚C)
100 125
3417 G18
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LTC3417Awww.DataSheet4U.com
APPLICATIO S I FOR ATIO
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
–
∆IL1
2
I2
=
ILIM2
–
∆IL2
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 occurs
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
(∆VOUT) is determined by:
∆VOUT
≈
∆IL⎛⎝⎜ESRCOUT
+
8
•
fO
1
• COUT
⎞
⎠⎟
where fO= operating frequency, COUT = output capacitance
and ∆IL = ripple current in the inductor. The output ripple
is highest at maximum input voltage, since ∆IL increases
with input voltage. With ∆IL = 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. Alumi-
num electrolytic, special polymer, ceramic and dry tanta-
lum capacitors are all available in surface mount pack-
ages. The OS-CON semiconductor dielectric capacitor
available 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 capaci-
tance 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 is
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| Páginas | Total 20 Páginas | |
| PDF Descargar | [ Datasheet LTC3417A.PDF ] | |
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