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PDF LTC3809 Data sheet ( Hoja de datos )
| Número de pieza | LTC3809 | |
| Descripción | Synchronous DC/DC Controller | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LTC3809
No RSENSE™, Low EMI,
Synchronous DC/DC Controller
FEATURES
www.datasheet4u.com
n No Current Sense Resistor Required
n Selectable Spread Spectrum Frequency Modulation
for Low Noise Operation
n Constant Frequency Current Mode Operation for
Excellent Line and Load Transient Response
n True PLL for Frequency Locking or Adjustment
(Frequency Range: 250kHz to 750kHz)
n Wide VIN Range: 2.75V to 9.8V
n Wide VOUT Range: 0.6V to VIN
n 0.6V ±1.5% Reference
n Low Dropout Operation: 100% Duty Cycle
n Selectable Burst Mode®/Pulse-Skipping/Forced
Continuous Operation
n Auxiliary Winding Regulation
n Internal Soft-Start Circuitry
n Output Overvoltage Protection
n Micropower Shutdown: IQ = 9μA
n Tiny Thermally Enhanced Leadless (3mm × 3mm)
DFN and 10-lead MSOP Packages
APPLICATIONS
n 1- or 2-Cell Lithium-Ion Powered Devices
n Portable Instruments
n Distributed DC Power Systems
DESCRIPTION
The LTC®3809 isasynchronousstep-downswitchingregu-
lator controller that drives external complementary power
MOSFETs using few external components. The constant
frequency current mode architecture with MOSFET VDS
sensing eliminates the need for a current sense resistor
and improves efficiency.
For noise sensitive applications, the LTC3809 can be exter-
nally synchronized from 250kHz to 750kHz. Burst Mode is
inhibited during synchronization or when the SYNC/MODE
pin is pulled low to reduce noise and RF interference. To
further reduce EMI, the LTC3809 incorporates a novel
spread spectrum frequency modulation technique.
Burst Mode operation provides high efficiency operation
at light loads. 100% duty cycle provides low dropout
operation, extending operating time in battery-powered
systems.
The switching frequency can be programmed up to 750kHz,
allowing the use of small surface mount inductors and
capacitors.
The LTC3809 is available in tiny footprint thermally
enhanced DFN and 10-lead MSOP packages.
L, LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology Corporation.
No RSENSE is a trademark of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
Protected by U.S. Patents including 5481178, 5929620, 6580258, 6304066, 5847554,
6611131, 6498466. Other Patents pending.
TYPICAL APPLICATION
High Efficiency, 550kHz Step-Down Converter
LTC3809
PLLLPF
VIN
VIN
2.75V TO 9.8V
10μF
187k
59k
15k
470pF
SYNC/MODE TG
VFB SW
ITH BG
RUN IPRG
GND
2.2μH
47μF
VOUT
2.5V
2A
3809 TA01
Efficiency and Power Loss vs Load Current
100
EFFICIENCY
VIN = 3.3V
90
VIN = 5V
VIN = 4.2V
80
10k
1k
100
POWER LOSS
70
VIN = 4.2V
10
60
50
1
1
FIGURE 10 CIRCUIT
VOUT = 2.5V
0.1
10 100 1000 10000
LOAD CURRENT (mA)
3809 TA01b
3809fc
1
1 page  
LTC3809
TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C unless otherwise noted.
Regulated Feedback Voltage
vs Temperature
www.da0t.a60s6heet4u.com
0.604
0.602
0.600
0.598
0.596
0.594
–60 –40 –20 0 20 40 60
TEMPERATURE (°C)
80 100
3809 G08
Maximum Current Sense
Threshold vs Temperature
135 IPRG = FLOAT
130
125
120
115
–60 –40 –20 0 20 40 60
TEMPERATURE (°C)
80 100
3809 G11
Oscillator Frequency
vs Input Voltage
5
4
3
2
1
0
–1
–2
–3
–4
–5
2 3456 78
INPUT VOLTAGE (V)
9 10
3809 G14
Undervoltage Lockout Threshold
vs Temperature
2.55
2.50
VIN RISING
2.45
2.40
2.35
2.30
VIN FALLING
2.25
2.20
2.15
–60 –40 –20 0 20 40 60
TEMPERATURE (°C)
80 100
3809 G09
SYNC/MODE Pull-Down Current
vs Temperature
2.80
2.75
2.70
2.65
2.60
2.55
2.50
2.45
2.40
–60 –40 –20 0 20 40 60
TEMPERATURE (°C)
80 100
3809 G12
Shutdown Quiescent Current
vs Input Voltage
18
16
14
12
10
8
6
4
2
0
2 3 4 5 6 7 8 9 10
INPUT VOLTAGE (V)
3809 G15
Shutdown (RUN) Threshold
vs Temperature
1.20
1.15
1.10
1.05
1.00
–60 –40 –20 0 20 40 60
TEMPERATURE (°C)
80 100
3809 G10
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
3809 G13
Sleep Current vs Input Voltage
130
120
110
100
90
80
70
2 3 4 5 6 7 8 9 10
INPUT VOLTAGE (V)
3809 G16
3809fc
5
5 Page 
LTC3809
OPERATION (Refer to Functional Diagram)
Peak Current Sense Voltage Selection and Slope
Compensation (IPRG Pin)
wwwW.dahtaesnheteht4eu.LcTomC3809 controller is operating below 20%
duty cycle, the peak current sense voltage (between the
VIN and SW pins) allowed across the external P-channel
MOSFET is determined by:
ΔVSENSE(MAX)
=
A
•
VITH – 0.7V
10
where A is a constant determined by the state of the IPRG
pin. Floating the IPRG pin selects A = 1; tying IPRG to VIN
selects A = 5/3; tying IPRG to GND selects A = 2/3. The
maximum value of VITH is typically about 1.98V, so the
maximum sense voltage allowed across the external P-
channel MOSFET is 125mV, 85mV or 204mV for the three
respective states of the IPRG pin.
However, once the controller’s duty cycle exceeds 20%,
slope compensation begins and effectively reduces the
peak sense voltage by a scale factor (SF) given by the
curve in Figure 1.
The peak inductor current is determined by the peak sense
voltage and the on-resistance of the external P-channel
MOSFET:
IPK
=
ΔVSENSE(MAX)
RDS(ON)
110
100
90
80
70
60
50
40
30
20
10
0
0 10 20 30 40 50 60 70 80 90 100
DUTY CYCLE (%)
3809 F01
Figure 1. Maximum Peak Current vs Duty Cycle
3809fc
11
11 Page | ||
| Páginas | Total 24 Páginas | |
| PDF Descargar | [ Datasheet LTC3809.PDF ] | |
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