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PDF LTC3809-1 Data sheet ( Hoja de datos )
| Número de pieza | LTC3809-1 | |
| Descripción | Synchronous DC/DC Controller | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LTC3809-1
No RSENSETM, Low Input
Voltage, Synchronous DC/DC
Controller with Output Tracking
www.datasheet4u.com
FEATURES
DESCRIPTION
n Programmable Output Voltage Tracking
n No Current Sense Resistor Required
n Constant Frequency Current Mode Operation for
Excellent Line and Load Transient Response
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 Selectable Maximum Peak Current Sense Threshold
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 Notebook and Palmtop Computers, PDAs
n Portable Instruments
n Distributed DC Power Systems
The LTC®3809-1 is a synchronous step-down switching
regulator 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.
Optional Burst Mode operation provides high efficiency
operation at light loads. 100% duty cycle provides low
dropout operation, extending operating time in battery-
powered systems. Burst Mode is inhibited when the MODE
pin is pulled low to reduce noise and RF interference.
The LTC3809-1 allows either coincident or ratiometric
output voltage tracking. Switching frequency is fixed at
550kHz. Fault protection is provided by an overvoltage
comparator and a short-circuit current limit comparator.
The LTC3809-1 is available in tiny footprint thermally
enhanced DFN and 10-lead MSOP packages.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. Burst
is a registered trademark 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
IPRG
VIN
VIN
2.75V TO 9.8V
10μF
MODE
TG
59k LTC3809-1
VFB
15k
SW
187k
470pF
ITH
RUN
BG
GND
2.2μH
47μF
VOUT
2.5V
2A
38091 TA01
Efficiency and Power Loss vs Load Current
100
EFFICIENCY
VIN = 3.3V
90
VIN = 5V
VIN = 4.2V
80
10k
1k
100
TYPICAL POWER
70 LOSS (VIN = 4.2V) 10
60
50
1
1
FIGURE 8 CIRCUIT
VOUT = 2.5V
0.1
10 100 1k 10k
LOAD CURRENT (mA)
38091 TA02
38091fc
1
1 page  
LTC3809-1
TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, unless otherwise noted.
Start-Up with Coincident Tracking
(VOUT = 0V at 0s)
www.datasheet4u.com
Vx
2.5V
VOUT
1.8V
Start-Up with Coincident Tracking
(VOUT = 0.8V at 0s)
Vx
2.5V
VOUT
1.8V
Start-Up with Ratiometric Tracking
(VOUT = 0V at 0s)
Vx
2.5V
VOUT
1.8V
500mV/DIV
500mV/DIV
500mV/DIV
10ms/DIV
VIN = 4.2V
RTA = 590
RTB = 1.18k
FIGURE 8 CIRCUIT
38091 G09
10ms/DIV
VIN = 4.2V
RTA = 590
RTB = 1.18k
FIGURE 8 CIRCUIT
38091 G10
10ms/DIV
VIN = 4.2V
RTA = 590
RTB = 1.69k
FIGURE 8 CIRCUIT
38091 G11
Regulated Feedback Voltage
vs Temperature
0.606
0.604
0.602
0.600
0.598
0.596
0.594
–60 –40 –20 0 20 40 60
TEMPERATURE (°C)
80 100
38091 G012
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
38091 G13
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
38091 G14
Maximum Current Sense
Threshold vs Temperature
135 IPRG = FLOAT
TRACK/SS Start-Up Current
vs Temperature
1.04
TRACK/SS = 0V
1.02
130
1.00
125
0.98
120
0.96
115
–60 –40 –20 0 20 40 60
TEMPERATURE (°C)
80 100
38091 G15
0.94
–60 –40 –20 0 20 40 60
TEMPERATURE (°C)
80 100
38091 G16
38091fc
5
5 Page 
LTC3809-1
OPERATION (Refer to Functional Diagram)
Dropout Operation
When the input supply voltage (VIN) approaches the output
wwwv.doalttaasghee,ett4hue.croamte of change of the inductor current while the
external P-channel MOSFET is on (ON cycle) decreases.
This reduction means that the P-channel MOSFET will
remain on for more than one oscillator cycle if the inductor
current has not ramped up to the threshold set by the
EAMP on the ITH pin. Further reduction in the input supply
voltage will eventually cause the P-channel MOSFET to be
turned on 100%; i.e., DC. The output voltage will then be
determined by the input voltage minus the voltage drop
across the P-channel MOSFET and the inductor.
Undervoltage Lockout
To prevent operation of the P-channel MOSFET below
safe input voltage levels, an undervoltage lockout is
incorporated in the LTC3809-1. When the input supply
voltage (VIN) drops below 2.25V, the external P- and
N-channel MOSFETs and all internal circuits are turned
off except for the undervoltage block, which draws only
a few microamperes.
Peak Current Sense Voltage Selection
and Slope Compensation (IPRG Pin)
When the LTC3809-1 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 (%)
38091 F01
Figure 1. Maximum Peak Current vs Duty Cycle
38091fc
11
11 Page | ||
| Páginas | Total 24 Páginas | |
| PDF Descargar | [ Datasheet LTC3809-1.PDF ] | |
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