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PDF LTC3565 Data sheet ( Hoja de datos )
| Número de pieza | LTC3565 | |
| Descripción | Synchronous Step-Down DC/DC Converter | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LTC3565www.DataSheet4U.com
1.25A, 4MHz, Synchronous
Step-Down DC/DC Converter
Features
n High Efficiency: Up to 95%
n VIN Range: 2.5V to 5.5V
n High Frequency Operation: Up to 4MHz
n Selectable Low Ripple (Typical 25mVp-p)
Burst Mode® Operation: IQ = 40µA
n Stable with Ceramic Capacitors
n Uses Tiny Capacitors and Inductor
n Low RDS(ON) Internal Switches: 0.15Ω
n Current Mode Operation for Excellent Line
and Load Transient Response
n Short-Circuit Protected
n Low Dropout Operation: 100% Duty Cycle
n Low Shutdown Current: IQ ≤ 1µA
n Output Voltages from 0.6V to 5V
n Synchronizable to External Clock
n Supports Pre-Biased Outputs
n Small 10-Lead (3mm × 3mm) DFN or MSOP Package
Applications
n Notebook Computers
n Digital Cameras
n Cellular Phones
n Handheld Instruments
n Board Mounted Power Supplies
Description
The LTC®3565 is a constant frequency, synchronous
step-down DC/DC converter. Intended for medium power
applications, it operates from a 2.5V to 5.5V input voltage
range and has a user-configurable operating frequency up
to 4MHz, allowing the use of tiny, low cost capacitors and
inductors 1mm or less in height. The output voltage is
adjustable from 0.6V to 5.5V. Internal synchronous power
switches provide high efficiency. The LTC3565’s current
mode architecture and external compensation allow the
transient response to be optimized over a wide range of
loads and output capacitors.
The LTC3565 can be configured for automatic power
saving Burst Mode operation (IQ = 40µA) to reduce gate
charge losses when the load current drops below the level
required for continuous operation. For reduced noise and
RF interference, the SYNC/MODE pin can be configured to
skip pulses or provide forced continuous operation.
To further maximize battery life, the P-channel MOSFET
is turned on continuously in dropout (100% duty cycle).
In shutdown, the device draws <1µA.
L, LT, LTC, LTM, Linear Technology the Linear logo, Burst Mode and OPTI-LOOP are registered
trademarks of Linear Technology Corporation. Hot Swap and ThinSOT are trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
Protected by U.S. Patents including 5481178, 6580258, 6498466, 6611131.
Typical Application
12.1k
680pF
Step-Down 2.5V/1.25A Regulator
VIN
2.5V TO 5.5V
SYNC/MODE SVIN PVIN
RUN
PGOOD LTC3565
SW
ITH
RT
191k
VFB
GND
22µF
2.2µH
22pF
931k
294k
VOUT
2.5V
1.25A
22µF
3565 TA01a
Efficiency and Power Loss vs Output Current
100 1
90
80 0.1
70
60
50 0.01
40
30
20
10
0
0.1
VIN = 2.7V
VIN = 3.6V
VIN = 4.2V
0.001
0.0001
1 10 100 1000 10000
OUTPUT CURRENT (mA)
3565 TA01b
3565fa
1 page  
LTC3565www.DataSheet4U.com
T ypical Performance Characteristics
otherwise noted.
TJ = 25°C, VIN = 3.6V, fO = 1MHz, unless
Frequency Variation vs Input
Voltage
6
RDS(ON) vs Input Voltage
0.25
RDS(ON) vs Temperature
0.30
4
2
0
–2
–4
–6
–8
2.5
3.0 3.5 4.0 4.5 5.0
INPUT VOLTAGE (V)
5.5
3565 G10
0.20
0.15
0.10
0.05
MAIN SWITCH
SYNCHRONOUS SWITCH
0.0
2.5 3.0 3.5 4.0 4.5 5.0 5.5
INPUT VOLTAGE (V)
3565 G11
0.25
0.20
0.15
0.10
0.05
0.0
–50 –25
MAIN SWITCH
SYNCHRONOUS SWITCH
0 25 50 75
TEMPERATURE (°C)
100 125
3565 G12
Dynamic Supply Current vs Input
Voltage
100
10 FORCED CONTINUOUS
1
PULSE SKIP
0.1
Burst Mode
OPERATION
0.01
VOUT = 1.8V
ILOAD = 0A
0.001
2.5 3.0 3.5 4.0 4.5 5.0 5.5
INPUT VOLTAGE (V)
3565 G13
Dynamic Supply Current vs
Temperature
100
10 FORCED CONTINUOUS
1
PULSE SKIP
0.1
Burst Mode
OPERATION
0.01
0.001
–50 –25
VOUT = 1.8V
ILOAD = 0A
0 25 50 75 100 125
TEMPERATURE (°C)
3565 G14
Switch Leakage vs Input Voltage
2500
2000
1500
MAIN SWITCH
1000
SYNCHRONOUS SWITCH
500
0
012 345 6
INPUT VOLTAGE (V)
3565 G15
3565fa
5 Page 
Applications Information
A general LTC3565 application circuit is shown in
Figure 4. External component selection is driven by the load
requirement, and begins with the selection of the inductor
L1. Once L1 is chosen, CIN and COUT can be selected.
Operating Frequency
Selection of the operating frequency is a trade-off between
efficiency and component size. High frequency operation
allows the use of smaller inductor and capacitor values.
Operation at lower frequencies improves efficiency by
reducing internal gate charge losses but requires larger
inductance values and/or capacitance to maintain low
output ripple voltage.
The operating frequency, fO, of the LTC3565 is determined
by an external resistor that is connected between the RT
pin and ground. The value of the resistor sets the ramp
current that is used to charge and discharge an internal
timing capacitor within the oscillator and can be calculated
by using the following equation:
RT = 1.21 × 106 (fO)–1.2674 (kΩ)
where RT is in kΩ and fO is in kHz or can be selected
using Figure 1.
The maximum usable operating frequency is limited by
the minimum on-time and the duty cycle. This can be
calculated as:
fO(MAX) ≈ 6.67 •
VOUT
VIN(MAX )
(MHz)
The minimum frequency is limited by leakage and noise
coupling due to the large resistance of RT.
Inductor Selection
The operating frequency, fO, has a direct effect on the
inductor value, which in turn influences the inductor ripple
current, ΔIL:
ΔIL
=
VOUT
fO • L
•
⎛⎝⎜1−
VOUT
V IN
⎞
⎠⎟
The inductor ripple current decreases with larger induc-
tance or frequency, and increases with higher VIN or VOUT.
Accepting larger values of ΔIL allows the use of lower
LTC3565www.DataSheet4U.com
inductances, but results in higher output ripple voltage,
greater core loss and lower output capability.
A reasonable starting point for setting ripple current is
ΔIL = 0.4 • IOUT(MAX), where IOUT(MAX) is 1.25A. The largest
ripple current ΔIL occurs at the maximum input voltage. To
guarantee that the ripple current stays below a specified
maximum, the inductor value should be chosen according
to the following equation:
L
=
VOUT
fO • ΔIL
• ⎛⎝⎜1−
V IVNO(MUTAX)⎞⎠⎟
The inductor value will also have an effect on Burst Mode
operation. The transition from low current operation
begins when the peak inductor current falls below a level
set by the burst clamp. Lower inductor values result in
higher ripple current which causes this to occur at lower
load currents. This causes a dip in efficiency in the upper
range of low current operation. In Burst Mode operation,
lower inductance values will cause the burst frequency
to increase.
5000
4500
TA = 25°C
4000
3500
3000
2500
2000
1500
1000
500
0
0 100 200 300 400 500 600
RT (kΩ)
3565 F01
Figure 1. Frequency vs RT
Inductor Core Selection
Different core materials and shapes will change the
size/current and price/current relationship of an induc-
tor. Toroid or shielded pot cores in ferrite or permalloy
materials are small and don’t radiate much energy, but
generally cost more than powdered iron core inductors
with similar electrical characteristics. The choice of which
style inductor to use often depends more on the price vs
size requirements and any radiated field/EMI requirements
than on what the LTC3565 requires to operate. Table 1
3565fa
11
11 Page | ||
| Páginas | Total 22 Páginas | |
| PDF Descargar | [ Datasheet LTC3565.PDF ] | |
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