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PDF LTC3355 Data sheet ( Hoja de datos )
| Número de pieza | LTC3355 | |
| Descripción | 20V 1A Buck DC/DC | |
| Fabricantes | Linear | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de LTC3355 (archivo pdf) en la parte inferior de esta página. Total 20 Páginas | ||
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FEATURES
nn VIN Voltage Range: 3V to 20V
nn VOUT Voltage Range: 2.7V to 5V
nn 1A Current Mode Buck Main Regulator
nn 5A Boost Backup Regulator Powered from Single
Supercapacitor
nn Boost Regulator Operates Down to 0.5V for
Maximum Utilization of Supercapacitor Energy
nn Programmable Supercapacitor Charge Current to
1A with Overvoltage Protection
nn Charger Supports Single Cell CC/CV Battery Charging
nn Programmable VIN Current Limit
nn Programmable Boost Current Limit
nn VIN Power Fail Indicator
nn VCAP Power Good Indicator
nn VOUT Power On Reset Output
nn Compact 20-Lead 4mm × 4mm QFN Package
APPLICATIONS
nn Ride-Through “Dying Gasp” Supplies
nn Power Meters/Industrial Alarms/Solid State Drives
LTC3355
20V 1A Buck DC/DC with
Integrated SCAP Charger
and Backup Regulator
DESCRIPTION
The LTC®3355 is a complete input power interrupt ride-
through DC/DC system. The part charges a supercapacitor
while delivering load current to VOUT, and uses energy from
the supercapacitor to provide continuous VOUT backup
power when VIN power is lost. The LTC3355 contains a
nonsynchronous constant frequency current mode mono-
lithic 1A buck switching regulator to provide a 2.7V to 5V
regulated output voltage from an input supply of up to 20V.
A 1A programmable CC/CV linear charger charges the
supercapacitor from VOUT. When the VIN supply drops
below the PFI threshold, the devices’s constant frequency
nonsynchronous current mode 5A boost switching
regulator delivers power from the supercapacitor to VOUT.
A thermal regulation loop maximizes charge current while
limiting the die temperature to 110°C. The IC has boost,
charger and VIN programmablecurrent limits. The LTC3355
is available in a 20-lead 4mm × 4mm QFN surface mount
package.
L, LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their respective
owners.
TYPICAL APPLICATION
Supercapacitor Charger and Ride-Through Power Supply
VIN
12V 10µF
0.091Ω
10µF
2.49M
200k
5 VIN
1µF
6 VINM5
4 VINS
1 PFI
SW1 7
PFO BUCK VOUT 15
1A
FB 2
10 PFOB
13 RSTB
9 CPGOOD
8 EN_CHG
3 MODE
INTVCC
18
LTC3355
BOOST
ICHG
12
VCAP 14
SW2
16
17
CFB 11
IBSTPKVCBST 19
20
1µF 60.4k 200k
6.8µH
4.7pF 402k
100k
3.3µH
665k
154k
220pF
3355 TA01a
332k
VOUT
4V
47µF 1A (MAX)
2.4V
SCAP
1F TO 50F
Backup Operation
14
CAPACITOR = 3F
12 IVOUT = 0.125A
10
VIN
8
6
4 VOUT
2 VCAP
0
0 5 10 15 20
TIME (SECONDS)
3355 TA01b
For more information www.linear.com/LTC3355
3355fb
1
1 page  
LTC3355
TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C unless otherwise noted
Buck Efficiency
100
90
80
70
60
50
40
30 VOUT = 4V
20
MODE = HIGH
VIN = 18V
10
VIN = 12V
VIN = 6V
0
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
LOAD CURRENT (A)
3355 G01
Maximum Boost Load Current
1.2 VOUT = 4V
1.0
0.8
0.6
0.4
0.2
0
0.75 1.25 1.75 2.25 2.75 3.25 3.75
VCAP (V)
3355 G04
Buck Frequency
vs Feedback Voltage
1000
900
800
700
600
500
400
300
200
100
0
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5
FB (V)
3355 G07
Boost Efficiency
100
90
80
70
60
50
40
30 VCAP = 2.4V
20
MODE = HIGH
VOUT = 3.3V
10
VOUT = 4V
VOUT = 5V
0
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
LOAD CURRENT (A)
3355 G02
Buck Switch Voltage Drop
700
600
500
400
300
200
100
0
0 100 200 300 400 500 600 700 800 900 1000
SWITCH CURRENT (mA)
3355 G05
Typical Minimum Buck Input
Voltage (VOUT = 3.3V)
4.6 VOUT = 3.3V
4.4
L = 6.8µH
INPUT CURRENT SET RESISTOR = 0.05Ω
4.2
4.0
3.8
3.6
3.4
3.2
3.0
1
10 100
VOUT LOAD CURRENT (mA)
1000
3355 G08
For more information www.linear.com/LTC3355
Maximum Buck Load Current
1.20
1.00
0.80
0.60
0.40
0.20 VOUT = 4V
L = 6.8µH
INPUT CURRENT SET RESISTOR = 0Ω
0
4 6 8 10 12 14 16 18
VIN (V)
20
3355 G03
Oscillator Frequency
vs Temperature
1200
1150
1100
1050
1000
950
900
850
800
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
3355 G06
Typical Minimum Buck Input
Voltage (VOUT = 5V)
6.3 VOUT = 5V
6.1 L = 6.8µH
INPUT CURRENT SET RESISTOR = 0.05Ω
5.9
5.7
5.5
5.3
5.1
4.9
4.7
4.5
1
10 100
VOUT LOAD CURRENT (mA)
1000
3355 G09
3355fb
5
5 Page 
LTC3355
OPERATION
0.8V reference voltage and turns the charger off when
these voltages are the same. The VCAP voltage represents
the fully charged supercapacitor voltage available to sup-
ply the boost regulator when VIN has dropped out. When
CFB decays to 30mV below the CFB reference voltage the
charger will be turned on. The LTC3355 includes a soft-
start circuit to minimize the inrush current at the start of
charge. When the charger is enabled, the charge current
ramps from zero to full-scale over a period of approximately
1ms. This has the effect of minimizing the transient load
current on VOUT.
The VCAP output also has an overvoltage protection cir-
cuit which monitors the CFB voltage. If the CFB voltage
increases above the CFB reference voltage by 35mV a
hysteretic comparator switches in an 8k resistor from
VCAP to ground. This will bleed any excess charge from
the supercapacitor. When the CFB voltage decays to the
CFB reference voltage the comparator will remove the
8k bleed resistor. Excess charge can come from leakage
currents associated with the boost rectifier diode.
VIN Status Monitor
The PFI input always monitors the VIN voltage and de-
termines when VIN is in dropout. VIN is divided down
by an external resistor divider and this voltage is then
compared to a reference voltage of 0.8V. If the PFI volt-
age is below the reference voltage the buck regulator and
the charger will be disabled and the boost regulator will
be enabled. The PFOB pin is a 5V open-drain output. This
pin is driven internally by the PFI comparator. When the
PFI comparator determines that VIN has dropped out the
PFOB output switches low. PFOB is normally connected
to a low voltage supply, via an external pull-up resistor.
The pull-up resistor for this output can be connected to
VOUT if another supply is not available.
VOUT Status Monitor
The RSTB pin is a 5V open-drain output. An internal
comparator determines when VOUT has reached 92.5% of
the programmed regulation voltage which then switches
the RSTB pin high. RSTB is normally connected to a low
voltage supply (VOUT) via an external pull-up resistor.
VCAP Status Monitor
The CPGOOD pin is a 5V open-drain output. An internal
comparator determines when VCAP has reached 92.5% of
the programmed regulation voltage which then switches
the CPGOOD pin high. CPGOOD is normally connected to a
low voltage supply (VOUT) via an external pull-up resistor.
Thermal Regulation
As the die temperature increases due to internal power
dissipation, a thermal regulator will limit the die tem-
perature to 110°C by reducing the charger current. The
thermal regulation protects the LTC3355 from excessive
temperature and allows the user to push the limits of the
power handling capability of a given circuit board without
the risk of damaging the LTC3355. Another feature is that
the charge current can be set according to typical, rather
than worst-case ambient temperatures for a given applica-
tion with the assurance that the charger will automatically
reduce the charge current in worst-case conditions.
Thermal Shutdown
The LTC3355 includes a thermal shutdown circuit in ad-
dition to the thermal regulator. If for any reason, the die
temperature exceeds 155°C, the entire part shuts down.
The part will resume normal operation once the temperature
drops about 15°C, to approximately 140°C.
VOUT Overvoltage, Undervoltage Lockout
The LTC3355 includes an overvoltage protection circuit
to ensure that VOUT does not exceed 5.65V (nominal).
An internal resistor divider from VOUT is connected to an
amplifier that will regulate VOUT as the overvoltage limit
is reached. The LTC3355 includes undervoltage lockout
which disables the boost when VOUT is < 2V typical.
For more information www.linear.com/LTC3355
3355fb
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11 Page | ||
| Páginas | Total 20 Páginas | |
| PDF Descargar | [ Datasheet LTC3355.PDF ] | |
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