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PDF LTC3736-1 Data sheet ( Hoja de datos )
| Número de pieza | LTC3736-1 | |
| Descripción | Synchronous Controller | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LTC3736-1www.DataSheet4U.com
Dual 2-Phase, No RSENSETM,
Synchronous Controller with
Spread Spectrum
FEATURES
■ Spread Spectrum Operation
■ Tracking Function
■ No Current Sense Resistors Required
■ Out-of-Phase Controllers Reduce Required
Input Capacitance
■ Wide VIN Range: 2.75V to 9.8V
■ Current Mode Operation
■ 0.6V ±1.5% Voltage Reference
■ Low Dropout Operation: 100% Duty Cycle
■ Pulse Skipping Operation at Light Loads
■ Internal Soft-Start Circuitry
■ Power Good Output Voltage Monitor
■ Output Overvoltage Protection
■ Micropower Shutdown: IQ = 9µA
■ Tiny Low Profile (4mm × 4mm) QFN and Narrow
SSOP Packages
U
APPLICATIO S
■ One or Two Lithium-Ion Powered Devices
■ Notebook and Palmtop Computers, PDAs
■ Portable Instruments
■ Distributed DC Power Systems
, LTC and LT are registered trademarks of Linear Technology Corporation.
No RSENSE is a trademark of Linear Technology Corporation.
Protected by U.S. Patents including 5481178, 5929620, 6144194, 6580258, 6304066,
6611131, 6498466.
DESCRIPTIO
The LTC®3736-1 is a 2-phase dual synchronous step-
down switching regulator controller with tracking that
drives external complementary power MOSFETs using
few external components. The constant frequency current
mode architecture with MOSFET VDS sensing eliminates
the need for sense resistors and improves efficiency.
Power loss and noise due to the ESR of the input capaci-
tance are minimized by operating the two controllers out
of phase.
A unique spread spectrum architecture randomly varies
the LTC3736-1’s switching frequency from 450kHz to
580kHz, significantly reducing the peak radiated and con-
ducted noise on both the input and output supplies,
making it easier to comply with electromagnetic interfer-
ence (EMI) standards.
Pulse skipping operation provides high efficiency at light
loads. 100% duty cycle capability provides low dropout op-
eration, extending operating time in battery-powered sys-
tems. The high switching frequencies allow for the use of
small surface mount inductors and capacitors.
The LTC3736-1 is available in the low profile (0.75mm)
24-pin thermally enhanced (4mm × 4mm) QFN package
and 24-lead narrow SSOP packages.
TYPICAL APPLICATIO
Low Noise, 2-Phase, Dual Synchronous DC/DC Step-Down Converter
VIN
SENSE1+ SENSE2+
10µF
×2
VIN
2.75V TO 9.8V
2.2µH
TG1 TG2
SW1 SW2
LTC3736-1
BG1 BG2
2.2µH
VOUT1
2.5V
+
187k
47µF
220pF
59k
PGND
PGND
VFB1
VFB2
ITH1 ITH2
SGND
15k
220pF
15k
118k
+
59k
VOUT2
1.8V
47µF
37361 TA01a
Output Voltage Frequency
Spectrum
–10
FIGURE 13 CIRCUIT SPREAD SPECTRUM
–20 VOUT = 2.5V
DISABLED
–30 RBW = 30Hz
SPREAD SPECTRUM
–40 ENABLED
–50
–60
–70
–80
–90
–100
–110
410k
450k 490k 530k 570k
FREQUENCY (Hz)
610k
37361 TA01b
37361f
1
1 page  
LTC3736-1www.DataSheet4U.com
TYPICAL PERFOR A CE CHARACTERISTICS TA = 25°C unless otherwise noted.
Maximum Current Sense Voltage
vs ITH Pin Voltage
100
80
60
40
20
0
–20
0.5
1 1.5
ITH VOLTAGE (V)
2
37361 G09
Efficiency and Power Lost vs
Load Current
10
FIGURE 13 CIRCUIT
VOUT = 2.5V
1
100
95
90
85
80
0.1 75
70
0.01
0.001
1
65
VIN = 5V
VIN = 3.3V
60
VIN = 4.2V 55
VIN = 7.2V 50
10 100 1000 10000
LOAD CURRENT (mA)
37361 G10
Regulated Feedback Voltage
vs Temperature
0.609
0.607
0.605
0.603
0.601
0.599
0.597
0.595
0.593
0.591
–60 –40 –20 0 20 40 60
TEMPERATURE (°C)
80 100
37361 G11
Shutdown (RUN) Threshold
vs Temperature
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
–60 –40 –20 0 20 40 60 80 100
TEMPERATURE (°C)
37361 G12
Maximum Current Sense Threshold
vs Temperature
135 IPRG = FLOAT
130
125
120
115
–60 –40 –20 0 20 40 60
TEMPERATURE (°C)
80 100
37361 G14
Oscillator Frequency
vs Temperature
10
SSDIS = VIN
8
6
4
2
0
–2
–4
–6
–8
–10
–60 –40 –20 0 20 40 60 80 100
TEMPERATURE (°C)
37361 G15
Efficiency vs Load Current
100
FIGURE 13 CIRCUIT
95 VOUT = 2.5V
90 VIN = 5V
85
80
75
70
65
60
55 SPREAD SPECTRUM
50 CONSTANT 550kHz
1 10 100 1000 10000
LOAD CURRENT (mA)
37361 G19
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
37361 G13
Undervoltage Lockout Threshold
vs Temperature
2.50
2.45
VIN RISING
2.40
2.35
2.30
VIN FALLING
2.25
2.20
2.15
2.10
–60 –40 –20 0 20 40 60
TEMPERATURE (°C)
80 100
37361 G16
37361f
5
5 Page 
U
OPERATIO (Refer to Functional Diagram)
operation enabled) with VIN = 5V, VOUT = 2.5V and IOUT =
1A. Note the significant reduction in peak output noise
(>20dBm).
Short-Circuit Protection
When an output is shorted to ground (VFB < 0.12V), the
switching frequency of that controller is reduced to 1/5 of
the normal operating frequency. The other controller is
unaffected and maintains normal operation.
The short-circuit threshold on VFB2 is based on the smaller
of 0.12V and a fraction of the voltage on the TRACK pin.
This also allows VOUT2 to start up and track VOUT1 more
easily. Note that if VOUT1 is truly short-circuited
(VOUT1 = VFB1 = 0V), then the LTC3736-1 will try to
regulate VOUT2 to 0V if a resistor divider on VOUT1 is
connected to the TRACK pin.
LTC3736-1www.DataSheet4U.com
Output Overvoltage Protection
As a further protection, the overvoltage comparator (OV)
guards against transient overshoots, as well as other more
serious conditions that may overvoltage the output. When
the feedback voltage on the VFB pin has risen 13.33%
above the reference voltage of 0.6V, the external P-chan-
nel MOSFET is turned off and the N-channel MOSFET is
turned on until the overvoltage is cleared.
Frequency Selection (FREQ Pin)
(Spread Spectrum Operation Disabled)
The switching frequency of the LTC3736-1 can be selected
using the FREQ pin when spread spectrum operation is
disabled (SSDIS = VIN).
–10
RBW = 3kHz
–20
–30
–40
–50
–60
–70
–80
–90
–100
–110
0
6M 12M 18M 24M
FREQUENCY (Hz)
30M
37361 F01a
Figure 1a. Output Noise Spectrum of Conventional Buck
Switching Converter (LTC3736-1 with Spread Spectrum
Disabled) Showing Fundamental and Harmonic Frequencies
–10
RBW = 3kHz
–20
–30
–40
–50
–60
–70
–80
–90
–100
–110
0
6M 12M 18M 24M
FREQUENCY (Hz)
30M
37361 F01c
Figure 1c. Output Noise Spectrum of the LTC3736-1 Spread
Spectrum Buck Switching Converter. Note the Reduction in
Fundamental and Harmonic Peak Spectral Amplitude
Compared to Figure 1a.
–10
RBW = 30Hz
–20
–30
–40
–50
–60
–70
–80
–90
–100
–110
410k
450k 490k 530k 570k
FREQUENCY (Hz)
610k
37361 F01b
Figure 1b. Zoom-In of Fundamental Frequency of Conventional
Buck Switching Converter
–10
RBW = 30Hz
–20
–30
–40
–50
–60
–70
–80
–90
–100
–110
410k
450k 490k 530k 570k
FREQUENCY (Hz)
610k
37361 F01d
Figure 1d. Zoom-In of Fundamental Frequency of the
LTC3736-1 Spread Spectrum Switching Converter. Note the
>20dB Reduction in Peak Amplitude and Spreading of the
Frequency Spectrum (Between Approximately 450kHz and
580kHz) Compared to Figure 1b.
37361f
11
11 Page | ||
| Páginas | Total 28 Páginas | |
| PDF Descargar | [ Datasheet LTC3736-1.PDF ] | |
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