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PDF LTC3737 Data sheet ( Hoja de datos )
| Número de pieza | LTC3737 | |
| Descripción | No RSENSE DC/DC Controller | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de LTC3737 (archivo pdf) en la parte inferior de esta página. Total 24 Páginas | ||
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LTC3737
Dual 2-Phase, No RSENSETM,
DC/DC Controller with
Output Tracking
FEATURES
s Sense Resistor Optional
s Out-of-Phase Controllers Reduce Required
Input Capacitance
s Programmable Output Voltage Tracking
www.DataShseetC4Uo.ncosmtant Frequency Current Mode Architecture
s Wide VIN Range: 2.75V to 9.8V
s Wide VOUT Range: 0.6V to VIN
s 0.6V ±1.5% Reference
s Low Dropout Operation: 100% Duty Cycle
s True PLL for Frequency Locking or Adjustment
(Frequency Range 250kHz to 850kHz)
s Selectable Burst Mode® or Pulse Skipping Operation
at Light Loads
s Internal Soft-Start Circuitry
s Selectable Maximum Peak Current Sense Threshold
s Power Good Output Voltage Monitor
s Output Overvoltage Protection
s Micropower Shutdown: IQ = 9µA
s Tiny 4mm × 4mm QFN and 24-Lead SSOP Packages
U
APPLICATIO S
s One or Two Lithium-Ion Powered Devices
s Notebook and Palmtop Computers, PDAs
s Portable Instruments
s Distributed DC Power Systems
DESCRIPTIO
The LTC®3737 is a 2-phase dual step-down switching
regulator controller that requires few external compo-
nents. The constant frequency current mode architecture
provides excellent AC and DC load and line regulation.
MOSFET VDS sensing eliminates the need for current
sense resistors and improves efficiency. Power loss and
noise due to the ESR of the input capacitance are mini-
mized by operating the two controllers out of phase.
Burst Mode operation provides high efficiency operation
at light loads. 100% duty cycle provides low dropout
operation and extends battery operating time.
Switching frequency can be programmed up to 750kHz,
allowing the use of small surface mount inductors and
capacitors. For noise sensitive applications, the LTC3737
can be externally synchronized from 250kHz to 850kHz.
Other features include a power good output voltage moni-
tor, a tracking input and internal soft-start.
The LTC3737 is available in the low profile thermally
enhanced (4mm × 4mm) QFN package or a 24-lead SSOP
narrow package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a registered trademark of Linear Technology Corporation.
No RSENSE is a trademark of Linear Technology Corporation.
U.S. patent numbers 5481178, 5731694, 5929620, 6144194,6580258, 5994885
TYPICAL APPLICATIO
187k
59k
15k
220pF
220pF
15k
59k
118k
SW1 SENSE1+
VFB1
PVIN1
ITH1 PGATE1
PGOOD
VIN
LTC3737
SGND
PGND
TRACK
RUN/SS
ITH2
VFB2
SW2
PGATE2
PVIN2
SENSE2+
VIN
2.75V TO
M1 2.2µH
+
9.8V
VOUT1
2.5V
D1 47µF
10µF
×2
D2 47µF
2.2µH
M2
3737 F01
VOUT2
1.8V
Figure 1. High Efficiency, 2-Phase, 550kHz Dual Step-Down Converter
Efficiency vs Load Current
100
VIN = 3.3V
95
90
VOUT = 2.5V
85
VOUT = 1.8V
80
75
70
65
60
55
50
1
10 100 1000
LOAD CURRENT (mA)
10000
3737 F01b
3737f
1
1 page  
TYPICAL PERFOR A CE CHARACTERISTICS
LTC3737
Undervoltage Lockout Threshold
vs Temperature
2.50
2.45
VIN RISING
2.40
2.35
2.30
www.DataShee2t.42U5 .com
VIN FALLING
2.20
2.15
2.10
–60 –40 –20 0 20 40 60
TEMPERATURE (°C)
80 100
3737 G10
Oscillator Frequency
vs Input Voltage
5
TA = 25°C
4
3
2
1
0
–1
–2
–3
–4
–5
23 4 56 78
INPUT VOLTAGE (V)
9 10
3737 G13
RUN/SS Pull-Up Current
vs Temperature
1.0
0.9
0.8
0.7
0.6
0.5
0.4
–60 –40 –20 0 20 40 60
TEMPERATURE (°C)
80 100
3737 G11
Shutdown Quiescent Current
vs Input Voltage
20
18
TA = 25°C
RUN/SS = 0V
16
14
12
10
8
6
4
2
0
2 3 4 5 6 7 8 9 10
INPUT VOLTAGE (V)
3737 G14
Oscillator Frequency
vs Temperature
10
8
6
4
2
0
–2
–4
–6
–8
–10
–60 –40 –20 0 20 40 60
TEMPERATURE (°C)
80 100
3737 G12
RUN/SS Start-Up Current
vs Input Voltage
0.9
TA = 25°C
0.8 RUN/SS = 0V
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
2345678
INPUT VOLTAGE (V)
9 10
3737 G15
3737f
5
5 Page 
U
OPERATIO (Refer to Functional Diagram)
Single Phase
Dual Controller
2-Phase
Dual Controller
SW1 (V)
SW2 (V)
www.DataSheet4IUL1.com
LTC3737
RMS input current and voltage. Significant cost and board
footprint savings are also realized by being able to use
smaller, less expensive, lower RMS current-rated, input
capacitors.
Of course the improvement afforded by 2-phase operation
is a function of the relative duty cycles of the two control-
lers, which in turn are dependent upon the input supply
voltage. Figure 4 depicts how the RMS input current varies
for single phase and 2-phase dual controllers with 2.5V
and 1.8V outputs over a wide input voltage range.
IL2
IIN
Figure 3. Example Waveforms for a Single Phase
Dual Controller vs the 2-Phase LTC3737
3737 F03
a load current of 2A, are derived from a 7V (e.g., a 2-cell
Li-Ion battery) input supply. In this example, 2-phase
operation would reduce the RMS input capacitor current
from 1.79ARMS to 0.91ARMS. While this is an impressive
reduction by itself, remember that power losses are pro-
portional to IRMS2, meaning that actual power wasted is
reduced by a factor of 3.86.
The reduced input ripple current also means that less
power is lost in the input power path, which could include
batteries, switches, trace/connector resistances, and pro-
tection circuitry. Improvements in both conducted and
radiated EMI also directly accrue as a result of the reduced
2.0
1.8
1.6 SINGLE PHASE
DUAL CONTROLER
1.4
1.2 2-PHASE
DUAL CONTROLER
1.0
0.8
0.6
0.4
0.2 VOUT1 = 2.5V/2A
VOUT2 = 1.8V/2A
0
23 4 5
6
78
9 10
INPUT VOLTAGE (V)
3737 F04
Figure 4. RMS Input Current Comparison
It can be readily seen that the advantages of 2-phase
operation are not limited to a narrow operating range, but
in fact extend over a wide region. A good rule of thumb for
most applications is that 2-phase operation will reduce the
input capacitor requirement to that for just one channel
operating at maximum current and 50% duty cycle.
3737f
11
11 Page | ||
| Páginas | Total 24 Páginas | |
| PDF Descargar | [ Datasheet LTC3737.PDF ] | |
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