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PDF LTC3600 Data sheet ( Hoja de datos )
| Número de pieza | LTC3600 | |
| Descripción | 1.5A Synchronous Rail-to-Rail Single Resistor Step-Down Regulator | |
| Fabricantes | Linear | |
| Logotipo |  |
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LTC3600
15V, 1.5A Synchronous
Rail-to-Rail Single Resistor
Step-Down Regulator
Features
n Single Resistor Programmable VOUT
n ±1% ISET Accuracy
n Tight VOUT Regulation Independent of VOUT Voltage
n Easy to Parallel for Higher Current and Heat Spreading
n Wide VOUT Range 0V to VIN – 0.5V
n High Efficiency: Up to 96%
n 1.5A Output Current
n Adjustable Frequency: 200kHz to 4MHz
n 4V to 15V VIN Range
n Current Mode Operation for Excellent Line and Load
Transient Response
n Zero Supply Current in Shutdown
n Available in Thermally Enhanced 12-Pin
(3mm × 3mm) DFN and MSOP Packages
Applications
n Voltage Tracking Supplies
n Point-of-Load Power Supplies
n Portable Instruments
n Distributed Power Systems
Description
The LTC3600 is a high efficiency, monolithic synchronous
buck regulator whose output is programmed with just one
external resistor. The accurate internally generated 50µA
current source on the ISET pin allows the use of a single
external resistor to program an output voltage that ranges
from 0V to 0.5V below VIN. The VOUT voltage feeds directly
back to the error amplifier in unity gain fashion and equals
the ISET voltage. The operating supply voltage range is 4V
to 15V, making it suitable for dual lithium-ion battery and
5V or 12V input point-of-load power supply applications.
The operating frequency is synchronizable to an external
clock or programmable from 200kHz to 4MHz with an
external resistor. High switching frequency allows the use
of small surface mount inductors. The unique constant
on-time architecture is ideal for operating at high frequency
in high step-down ratio applications that also demand fast
load transient response.
L, LT, LTC, LTM, Linear Technology, the Linear logo and OPTI-LOOP are registered trademarks
and Hot Swap is a trademark of Linear Technology Corporation. All other trademarks are the
property of their respective owners. Protected by U.S. Patents, including 5481178, 5705919,
5847554, 6580258.
Typical Application
High Efficiency, 1MHz, 1.5A Step-Down Converter
VIN
12V
VIN
8
LTC3600
9
BOOST
RUN 50µA
5
10µF
+
ERROR
AMP
–
PWM CONTROL
AND SWITCH
DRIVER
SW
7
0.1µF
2.2µH
ISET
1
MODE/
SYNC INTVCC RT
6 10 3
VOUT
11
GND PGFB
13 4
ITH PGOOD
2 12
3600 TA01a
0.1µF 49.9k
1µF
VOUT
2.5V
22µF
Efficiency and Power Loss vs
Output Current
100
90
VIN = 12V
VOUT = 2.5V
80 DCM
70
POWER
LOSS
1.0
0.9
0.8
0.7
60
50 CCM
40
0.6
0.5
0.4
30 0.3
20
10
0
0.001
CCM
DCM
0.01 0.1
1
LOAD CURRENT (A)
0.2
0.1
0
10
3600 TA01b
3600fc
1
1 page  
Typical Performance Characteristics
LTC3600
Load Regulation
100
99 VOUT
98
VISET
97
96
VIN = 12V
95 VOUT = 3.3V
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8
IOUT (A)
3600 G01
ISET Current Line Regulation
50.4
50.2
50.0
49.8
49.6
49.4
ISET (VISET = 0V)
49.2 ISET (VISET = 2.5V)
0 2 4 6 8 10 12 14 16 18
VIN
3600 G04
ISET Current vs Temperature
50.5
50.3
50.1
49.9
49.7
49.5
–50 –25
0 25 50 75 100 125 150
TEMPERATURE (°C)
3600 G02
Quiescent Current vs
Temperature
4.0
3.5 CCM
3.0
2.5
2.0
1.5
1.0 DCM
0.5
0
–100 –50
0
50 100 150 200
TEMPERATURE (°C)
3600 G05
ISET Current vs VISET
51
50
VIN =15V
49
48
47
46
45
44
0 2 4 6 8 10 12 14 16
VISET
3600 G03
Shutdown IQ vs VIN
1.0
0.9
VRUN = 0
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0 2 4 6 8 10 12 14 16
VIN
3600 G06
RDS(ON) vs Temperature
260
240
220 MTOP
200
180
160
140 MBOT
120
100
80
60
40
20
0
–50 0
50 100
TEMPERATURE (°C)
Transient Response CCM
Operation, External Compensation
Transient Response CCM
Operation, Internal Compensation
VOUT
100mV/DIV
AC-
COUPLED
VOUT
100mV/DIV
AC-
COUPLED
IL
1A/DIV
IL
1A/DIV
150
3600 G07
VIN = 12V
VOUT = 3.3V
IOUT = 0A TO 1A
L = 4.7µH
20µs/DIV
3600 G08
fSW = 1MHz
RITH = 27.5kΩ, CITH = 250pF
MODE = INTVCC
COUT = 47µF
VIN = 12V
VOUT = 3.3V
IOUT = 0A TO 1A
L = 4.7µH
20µs/DIV
fSW = 1MHz
ITH = INTVCC
MODE = INTVCC
COUT = 47µF
3600 G09
3600fc
5
5 Page 
LTC3600
Operation
RT value should be selected such that the external clock
frequency is within this 30% range of the RT programmed
frequency.
Output Voltage Tracking and Soft Start
The LTC3600 allows the user to program its output voltage
ramp rate by means of the ISET pin. Since VOUT servos its
voltage to that of the ISET pin, placing an external capaci-
tor CSET on the ISET pin will program the ramp-up rate of
the ISET pin and thus the VOUT voltage.
VOUT(t) = IISET • RSET
1−
e
−
RSET
t
•
C SET
fro m 0 to 9 0 % VOUT
t SS ≅ − RSET • CSET • n(1− 0 .9)
t SS 2 .3RSET • CSET
The soft-start time tSS (from 0% to 90% VOUT) is 2.3
times of time constant (RSET • CSET). The ISET pin can
also be driven by an external voltage supply capable of
sinking 50µA.
When starting up into a pre-biased VOUT, the LTC3600 will
stay in discontinuous mode and keep the power switches
off until the voltage on ISET has ramped up to be equal
to VOUT, at which point the switcher will begin switching
and VOUT will ramp up with ISET.
Output Power Good
When the LTC3600’s output voltage is within the 7.5%
window of the regulation point, which is reflected back
as a VPGFB voltage in the range of 0.555V to 0.645V, the
output voltage is in regulation and the PGOOD pin is
pulled high with an external resistor connected to INTVCC
or another voltage rail. Otherwise, an internal open-drain
pull-down device (200Ω) will pull the PGOOD pin low.
To prevent unwanted PGOOD glitches during transients
or dynamic VOUT changes, the LTC3600’s PGOOD falling
edge includes a blanking delay of approximately 20µs.
Internal/External ITH Compensation
For ease of use, the user can simplify the loop compen-
sation by tying the ITH pin to INTVCC to enable internal
compensation. This connects an internal 100k resistor
in series with a 50pF capacitor to the output of the error
amplifier (internal ITH compensation point). This is a
trade-off for simplicity instead of OPTI-LOOP® optimiza-
tion, where ITH components are external and are selected
to optimize the loop transient response with minimum
output capacitance.
Minimum Off-Time Considerations
The minimum off-time, tOFF(MIN), is the smallest amount
of time that the LTC3600 is capable of turning on the bot-
tom power MOSFET, tripping the current comparator and
turning the power MOSFET back off. This time is generally
about 50ns. The minimum off-time limit imposes a maxi-
mum duty cycle of tON/(tON + tOFF(MIN)). If the maximum
duty cycle is reached, due to a dropping input voltage
for example, then the output will drop out of regulation.
The minimum input voltage to avoid dropout is:
VI N(M I N)
=
VO U T
•
tON
+ tOFF(MIN)
tON
Conversely, the minimum on-time is the smallest dura-
tion of time in which the top power MOSFET can be in
its “on” state. This time is typically 20ns. In continuous
mode operation, the minimum on-time limit imposes a
minimum duty cycle of:
DMIN = fSW • tON(MIN)
Where tON(MIN) is the minimum on-time. As the equation
shows, reducing the operating frequency will alleviate the
minimum duty cycle constraint.
In the rare cases where the minimum duty cycle is sur-
passed, the output voltage will still remain in regulation, but
the switching frequency will decrease from its programmed
value. This is an acceptable result in many applications, so
this constraint may not be of critical importance in most
cases. High switching frequencies may be used in the
design without any fear of severe consequences. As the
sections on inductor and capacitor selection show, high
switching frequencies allow the use of smaller board com-
ponents, thus reducing the size of the application circuit.
3600fc
11
11 Page | ||
| Páginas | Total 28 Páginas | |
| PDF Descargar | [ Datasheet LTC3600.PDF ] | |
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