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PDF LTC3822 Data sheet ( Hoja de datos )
| Número de pieza | LTC3822 | |
| Descripción | Synchronous Step-Down DC/DC Controller | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de LTC3822 (archivo pdf) en la parte inferior de esta página. Total 20 Páginas | ||
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LTC3822
No RSENSETM, Low Input
Voltage, Synchronous Step-Down
DC/DC Controller
www.datasheet4u.com
FEATURES
DESCRIPTIO
■ No Current Sense Resistor Required
■ All N-Channel MOSFET Synchronous Drive
■ High Current Outputs Possible
■ Constant Frequency Current Mode Operation for
Excellent Line and Load Transient Response
■ VIN: 2.75V to 4.5V
■ ±1% 0.6V Reference
■ Low Dropout Operation: 99% Duty Cycle
■ Selectable Frequency (300kHz/550kHz/750kHz)
■ Internal Soft-Start Circuitry
■ Selectable Maximum Peak Current Sense Threshold
■ Digital RUN Control Pin
■ Output Overvoltage Protection
■ Micropower Shutdown: IQ = 7.5µA
■ Tiny Thermally Enhanced Leadless (3mm x 3mm)
DFN or 10-Lead MSOP Package
The LTC3822 is a synchronous step-down switching
regulator controller that drives external N-channel power
MOSFETs using few external components. The constant
frequency current mode architecture with MOSFET VDS
sensing eliminates the need for sense resistors and im-
proves efficiency.
A maximum duty cycle of 99% provides low dropout
operation. The switching frequency can be programmed
up to 750kHz, allowing the use of small surface mount
inductors and capacitors.
The LTC3822 is available in thermally enhanced DFN and
10-lead MSOP packages.
, LT, LTC and LTM 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.
U
APPLICATIO S
■ 3.3VIN Systems
■ Li-Ion Battery Systems
TYPICAL APPLICATIO
1.8V/8A High Efficiency, 550kHz Step-Down Converter
IPRG
VIN
RUN
TG
FREQ
LTC3822 SW
ITH
5.1k BOOST
680pF
GND
BG
VFB
59k 118k
0.22µF
FDS6898A
0.47µH
47µF
VIN
2.75V TO 4.5V
VOUT
1.8V
100µF 8A
3822 TA01
Efficiency and Power Loss vs
Load Current
100 VIN = 3.3V
90
80
EFFICIENCY
10
70 1
60
50
40
30
POWER LOSS
0.1
20
10
0
100
1000
LOAD CURRENT (mA)
0.01
10000
3822 TA01b
3822f
1
1 page  
LTC3822
TYPICAL PERFOR A CE CHARACTERISTICS TA = 25°C unless otherwise noted.
Regulated Feedback Voltage
vs Temperature
www.da0t.a6s0h4 eet4u.com
0.603
0.602
0.601
0.600
0.599
0.598
0.597
0.596
–50
0 50
TEMPERATURE (°C)
100
3822 G06
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
3822 G07
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
3822 G08
Maximum Current Sense
Threshold vs Temperature
130 IPRG = FLOAT
125
120
115
110
–60 –40 –20 0 20 40 60
TEMPERATURE (°C)
80 100
3822 G09
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
3822 G10
Oscillator Frequency
vs Input Voltage
5
4
3
2
1
0
–1
–2
–3
–4
–5
2.5
3.0 3.5 4.0
INPUT VOLTAGE (V)
4.5
3822 G11
Shutdown Quiescent Current
vs Input Voltage
18
16
14
12
10
8
6
4
2
0
2.5 3.0 3.5 4.0 4.5
INPUT VOLTAGE (V)
3822 G12
Quiescent Current in Normal
Operation vs Input Voltage
370
360
350
340
330
320
310
2.6
3.6
INPUT VOLTAGE (V)
4.6
3822 G13
3822f
5
5 Page 
LTC3822
APPLICATIO S I FOR ATIO
2.0
w w w . d a t1.a5 s h e e t 4 u . c o m
1.0
0.5
0
– 50
0 50 100
JUNCTION TEMPERATURE (°C)
150
3822 F02
Figure 2. RDS(ON) vs Temperature
The power dissipated in the MOSFETs strongly depends
on their respective duty cycles and load current. When the
LTC3822 is operating in continuous mode, the duty cycles
for the MOSFETs are:
Top MOSFET Duty Cycle = VOUT
VIN
Bottom MOSFET Duty Cycle =
VIN – VOUT
VIN
The MOSFET power dissipations at maximum output
current are:
PTOP
=
VOUT
VIN
• IOUT(MAX)2
• ρT
• RDS(ON)
+ 2 • VIN2
• IOUT(MAX) • CRSS • f
PBOT
=
VIN
– VOUT
VIN
• IOUT(MAX)2
• ρT
• RDS(ON)
Both MOSFETs have I2R losses and the PTOP equation
includes an additional term for transition losses, which are
largest at high input voltages. The bottom MOSFET losses
are greatest at high input voltage or during a short-circuit
when the bottom duty cycle is 100%.
The LTC3822 utilizes a non-overlapping, anti-shoot-
through gate drive control scheme to ensure that the
MOSFETs are not turned on at the same time. To function
properly, the control scheme requires that the MOSFETs
used are intended for DC/DC switching applications. Many
power MOSFETs are intended to be used as static switches
and therefore are slow to turn on or off.
Reasonable starting criteria for selecting the MOSFETs are
that they must typically have a gate charge (QG) less than
30nC (at 2.5VGS) and a turn-off delay (tD(OFF)) of less than
approximately 140ns. However, due to differences in test
and specification methods of various MOSFET manufac-
turers, and in the variations in QG and tD(OFF) with gate
drive (VIN) voltage, the MOSFETs ultimately should be
evaluated in the actual LTC3822 application circuit to
ensure proper operation.
Shoot-through between the MOSFETs can most easily be
spotted by monitoring the input supply current. As the
input supply voltage increases, if the input supply current
increases dramatically, then the likely cause is shoot-
through.
Operating Frequency
The choice of operating frequency, fOSC, is a trade-off
between efficiency and component size. Low frequency
operation improves efficiency by reducing MOSFET switch-
ing losses, both gate charge loss and transition loss.
However, lower frequency operation requires more induc-
tance for a given amount of ripple current.
3822f
11
11 Page | ||
| Páginas | Total 20 Páginas | |
| PDF Descargar | [ Datasheet LTC3822.PDF ] | |
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