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PDF LTC3619 Data sheet ( Hoja de datos )
| Número de pieza | LTC3619 | |
| Descripción | 400mA/800mA Synchronous Step-Down DC/DC | |
| Fabricantes | Linear | |
| Logotipo |  |
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LTC3619
Features
400mA/800mA Synchronous
Step-Down DC/DC with
Average Input Current Limit
Description
n Programmable Average Input Current Limit:
±5% Accuracy
n Dual Step-Down Outputs: Up to 96% Efficiency
n Low Ripple (<25mVP-P) Burst Mode® Operation:
IQ = 50µA
n Input Voltage Range: 2.5V to 5.5V
n Output Voltage Range: 0.6V to 5V
n 2.25MHz Constant-Frequency Operation
n Power Good Output Voltage Monitor for Each Channel
n Low Dropout Operation: 100% Duty Cycle
n Independent Internal Soft-Start for Each Channel
n Current Mode Operation for Excellent Line and Load
Transient Response
n ±2% Output Voltage Accuracy
n Short-Circuit Protected
n Shutdown Current ≤ 1μA
n Available in Small Thermally Enhanced 10-Lead MSE
and 3mm × 3mm DFN Packages
Applications
n High Peak Load Current Applications
n USB Powered Devices
n Supercapacitor Charging
n Radio Transmitters and Other Handheld Devices
The LTC®3619 is a dual monolithic synchronous buck
regulator using a constant frequency, current mode
architecture.
The input supply voltage range is 2.5V to 5.5V, making it
ideal for Li-Ion and USB powered applications. 100% duty
cycle capability provides low dropout operation, extend-
ing the run time in battery-operated systems. Low output
voltages are supported with the 0.6V feedback reference
voltage. Channel 1 and channel 2 can supply 400mA and
800mA output current, respectively.
The LTC3619’s programmable average input current limit
is ideal for USB applications and for point-of-load power
supplies because the LTC3619’s limited input current will
still allow its output to deliver high peak load currents
without collapsing the input supply. When the sum of both
channels’ currents exceeds theinput current limit, channel2
is current limited while channel 1 remains regulated. The
operating frequency is internally set at 2.25MHz allowing
the use of small surface mount inductors. Internal soft-start
reduces in-rush current during start-up. The LTC3619 is
available in small MSOP and 3mm × 3mm DFN packages
and is also available in a low noise, high efficiency pulse-
skipping version, LTC3619B.
L, LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode 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, 6127815,
6304066, 6498466, 6580258, 6611131.
Typical Application
Dual Monolithic Buck Regulator in 10-Lead 3mm × 3mm DFN
VIN
3.4V TO 5.5V
10µF
RUN2 VIN RUN1
PGOOD2 PGOOD1
VOUT2
3.4V AT
800mA
1.5µH
LTC3619
SW2 SW1
3.3µH
22pF
1190k
+
VFB2
VFB1
2.2mF
×2
255k
RLIM GND
SuperCap
1000pF 116k
255k 511k
ILIM = 475mA
VOUT1
1.8V AT
400mA
10µF
3619 TA01a
VOUT2
200mV/DIV
VIN
1V/DIV
AC-COUPLED
GSM Pulse Load
IOUT
500mA/DIV
IIN
500mA/DIV
1ms/DIV
3619 TA01b
VIN = 5V, 500mA COMPLIANT,
ILOAD = 0A TO 2.2A, CHANNEL 1 UNLOADED
3619fa
1
1 page  
LTC3619
Typical Performance Characteristics TA = 25°C, VIN = 5V, unless otherwise noted.
Efficiency vs Load Current
100
90
80
70
60
50
40
30
20
10 VOUT = 3.3V
CHANNEL 1
0
0.0001 0.001
0.01
VIN = 3.6V
VIN = 4.2V
VIN = 5V
0.1 1
OUTPUT CURRENT (A)
3619 G10
Efficiency vs Load Current
100
90
80
70
60
50
40
30
20
10 VOUT = 3.3V
0 CHANNEL 2
0.0001 0.001
0.01
VIN = 3.6V
VIN = 4.2V
VIN = 5V
0.1 1
OUTPUT CURRENT (A)
3619 G11
Efficiency vs Load Current
100
90
80
70
60
50
40
30
20
10 VOUT = 1.2V
0 CHANNEL 1
0.0001 0.001
0.01
VIN = 2.7V
VIN = 3.6V
VIN = 4.2V
VIN = 5V
0.1 1
OUTPUT CURRENT (A)
3619 G12
Efficiency vs Load Current
100
90
80
70
60
50
40
30
20
10 VOUT = 1.2V
0 CHANNEL 2
0.0001 0.001
0.01
VIN = 2.7V
VIN = 3.6V
VIN = 4.2V
VIN = 5V
0.1 1
OUTPUT CURRENT (A)
3619 G13
Load Regulation (Channel 1)
2.0
VOUT = 1.8V
1.5
VOUT = 2.5V
VOUT = 3.3V
1.0
0.5
0
–0.5
–1.0
–1.5
–2.0
0
100 200 300
LOAD CURRENT (mA)
400
3619 G14
Load Regulation (Channel 2)
2.0
VOUT = 1.8V
1.5
VOUT = 2.5V
VOUT = 3.3V
1.0
0.5
0
–0.5
–1.0
–1.5
–2.0
0
200 400 600
LOAD CURRENT (mA)
800
3619 G15
Line Regulation
0.6 VOUT = 1.8V
ILOAD = 100mA
0.4
0.2
0
–0.2
–0.4
–0.6
2.5 3.0 3.5 4.0 4.5 5.0 5.5
VIN (V)
3619 G16
3619fa
5
5 Page 
LTC3619
Operation
cycle. When an instantaneous 1A output pulse is applied,
the current out of the RLIM pin becomes 1A/55k = 18.2µA
during the 50% on-time or 9.1µA full duty cycle. With a
CLIM capacitor of 1µF, RLIM of 116k, and using I = CdV/dt,
it will take 110ms for CLIM to charge from 0V to 1V. This
is the time after which the LTC3619 will start input current
limiting. Any current within this time must be considered
in each application to determine if it is tolerable.
Figure 1a shows VIN (IIN) current below input current limit
with a CLIM capacitor of 0.1µF. Channel 1 is unloaded to
simplify calculations. When the load pulse is applied, under
the specified condition, ILIM current is 1.1A/55k•0.66 =
13.2µA, where 0.66 is the duty cycle. It will take a little
more than 7.5ms to charge the CLIM capacitor from 0V to
1V, after which the LTC3619 begins to limit input current.
The IIN current is not limited during this 7.5ms time and is
more than 725mA. This current transient may cause the
input supply to temporarily droop if the supply current
compliance is exceeded, but recovers after the input cur-
rent limit engages. The output will continue to deliver the
required current load while the output voltage droops to
allow the input voltage to remain regulated during input
current limit.
For applications with short load pulse duration, a smaller
CLIM capacitor may be the better choice as in the example
shown in Figure 1b. Channel 1 is unloaded for simplifi-
cation. In this example, a 577µs, 0A to 2A output pulse
is applied once every 4.7ms. A CLIM capacitor of 2.2nF
requires 92µs for VRLIM to charge from 0 to 1V. During
this 92µs, the input current limit is not yet engaged and
the output must deliver the required current load. This
may cause the input voltage to droop if the current com-
pliance is exceeded. Depending on how long this time is,
the VIN supply decoupling capacitor can provide some of
this current before VIN droops too much. In applications
with a bigger VIN supply decoupling capacitor and where
VIN supply is allowed to droop closer to dropout, the CLIM
capacitor can be increased slightly. This will delay the start
of input current limit and artificially regulated VOUT before
input current limit is engaged. In this case, within the 577µs
load pulse, VOUT voltage will stay artificially regulated for
92µs out of the total 577µs before the input current limit
activates. This approach may be used if a faster recovery
on the output is desired.
Selecting a very small CLIM will speed up response time
but it can put the device within threshold of interfering
with normal operation and input current limit in every
few switching cycles. This may be undesirable in terms
of noise. Use 2πRC >> 100/clock frequency (2.25MHz) as
a starting point, R being RLIM, C being CLIM.
VOUT
2V/DIV
IVIN
500mA/DIV
VRLIM
1V/DIV
IL
1A/DIV
50ms/DIV
3619 F01a
VIN = 5V, 500mA COMPLIANT,
RLIM = 116k, CLIM = 0.1µF
ILOAD = 0A TO 1.1A, COUT = 2.2mF, VOUT = 3.3V
ILIM = 475mA, CHANNEL 1 UNLOADED
Figure 1a. Input Current Limit Within 100ms Load Pulses
VOUT
200mV/DIV
VIN
1V/DIV
AC-COUPLED
IOUT
500mA/DIV
IIN
500mA/DIV
1ms/DIV
3619 F01b
VIN = 5V, 500mA COMPLIANT,
RLIM = 116k, CLIM = 2200pF
ILOAD = 0A TO 2A, COUT = 2.2mF, VOUT = 3.3V
ILIM = 475mA, CHANNEL 1 NOT LOADED
Figure 1b. Input Current Limit Within 577µs,
2A Repeating Load Pulses
3619fa
11
11 Page | ||
| Páginas | Total 22 Páginas | |
| PDF Descargar | [ Datasheet LTC3619.PDF ] | |
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