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PDF LT8616 Data sheet ( Hoja de datos )
| Número de pieza | LT8616 | |
| Descripción | Dual 42V Synchronous Monolithic Step-Down Regulator | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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Features
LT8616
Dual 42V Synchronous
Monolithic Step-Down Regulator
with 6.5µA Quiescent Current
Description
n Wide Input Voltage Range: 3.4V to 42V
n 2.5A and 1.5A Buck Regulators with Separate Inputs
n Fast Minimum Switch On-Time: 35ns
n Ultralow Quiescent Current Burst Mode® Operation:
n 6.5µA IQ Regulating 12VIN to 5VOUT and 3.3VOUT
n Output Ripple < 15mV
n 180° Out of Phase Switching
n Adjustable and Synchronizable: 200kHz to 3MHz
n Accurate 1V Enable Pin Thresholds
n Internal Compensation
n Output Soft-Start and Tracking
n TSSOP Package: Output Stays at or Below Regulation
Voltage During Adjacent Pin Short or When a Pin Is
Left Floating
n Thermally Enhanced 28-Lead TSSOP Package
Applications
n Automotive and Industrial Supplies
n General Purpose Step-Down
The LT®8616 is a high efficiency, high speed, dual synchro-
nous monolithic step-down switching regulator that con-
sumes only 6.5µA of quiescent current with both channels
enabled. Both channels contain all switches and necessary
circuitry to minimize the need for external components.
Low ripple Burst Mode operation enables high efficiency
down to very low output currents while minimizing output
ripple. A SYNC pin allows synchronization to an external
clock. Internal compensation with peak current mode
topology allows the use of small inductors and results in
fast transient response and good loop stability. The en-
able pins have accurate 1V thresholds and can be used to
program undervoltage lockout. Capacitors on the TR/SS
pins programs the output voltage ramp rate during start-
up while the PG pins signal when each output is within
10% of the programmed output voltage. The LT8616 is
available in a TSSOP package for high reliability.
L, LT, LTC, LTM, Burst Mode, Linear Technology and the Linear logo are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their respective
owners.
Typical Application
5V, 3.3V, 700kHz Step-Down Converter
VIN
12V
VIN1 BOOST1
4.7µF
EN/UV1
4.7µF
1M
10nF
1µF
56.2k
VIN2
EN/UV2
SW1
FB1
LT8616
PG1
PG2
SYNC/MODE
BIAS
BOOST2
TR/SS1
TR/SS2
INTVCC
SW2
RT GND FB2
0.1µF
10µH
1M
187k
0.1µF
4.7µH
1M
316k
5.6pF
VOUT1
5V, 1.5A
47µF
10pF
VOUT2
3.3V, 2.5A
2 x 47µF
8616 TA01a
100
90
80
70
60
50
40
30
0.01
0.1
Efficiency
VIN1 = VIN2 = 12V
fSW = 700kHz
1 10
LOAD (mA)
CH1, 5VOUT
CH2, 3.3VOUT
100 1000
8616 TA01b
For more information www.linear.com/LT8616
8616f
1
1 page  
Typical Performance Characteristics
LT8616
Efficiency at 5VOUT
100
98
fSW = 700kHz
96
94
92
90
88
86
84
CH1, 12VIN
CH1, 24VIN
82
CH2, 12VIN
CH2, 24VIN
80
0 0.25 0.5 0.75 1.0 1.25 1.5 1.75 2.0 2.25 2.5
LOAD (A)
8616 G01
Efficiency at 3.3VOUT
100
98 fSW = 700kHz
96
94
92
90
88
86
84
CH1, 12VIN
CH1, 24VIN
82
CH2, 12VIN
CH2, 24VIN
80
0 0.25 0.5 0.75 1.0 1.25 1.5 1.75 2.0 2.25 2.5
LOAD (A)
8616 G04
No Load Supply Current
30
VIN1 = VIN2 = 12V
VOUT1 = 5V
25 VOUT2 = 3.3V
IN REGULATION
20
15
10
5
0
–50 –25
0 25 50 75 100 125 150
TEMPERATURE (°C)
8616 G07
Efficiency at 5VOUT
100
95
fSW = 700kHz
90
85
80
75
70
65
60
55
50
45
40
35
30
0.01 0.1 1 10
LOAD (mA)
CH1, 12VIN
CH1, 24VIN
CH2, 12VIN
CH2, 24VIN
100 1000
8616 G02
Efficiency at 3.3VOUT
100
95 fSW = 700kHz
90
85
80
75
70
65
60
55
50
45
40
35
30
0.01 0.1 1 10
LOAD (mA)
CH1, 12VIN
CH1, 24VIN
CH2, 12VIN
CH2, 24VIN
100 1000
8616 G05
BIAS Current
vs Switching Frequency
18
16
14
12
10
8
6
VIN1 = VIN2 = 12V
4 VOUT1 = 5V
LOAD1 = 1A
2 VOUT2 = 3.3V
0 LOAD2 = 1A
0 0.5 1.0 1.5 2.0 2.5 3.0
FREQUENCY (MHz)
8616 G08
For more information www.linear.com/LT8616
Efficiency vs Frequency
95
94 VIN1 = VIN2 = 12V
93
92
91
90
89
88
87
86
CH1, 5V, 1A
CH2, 3.3V, 1.5A
85
0.2 0.6 1.0 1.4 1.8 2.2 2.6 3.0
FREQUENCY (MHz)
8616 G03
No Load Supply Current
10
9
8
7
6
5
4
3
2
1
VOUT1 = 3.3V
VOUT2 = 5V
0
0 5 10 15 20 25 30 35 40
VIN (V)
8616 G06
EN/UV Threshold
1.1
1.08
1.06
1.04
1.02
1.0
0.98
0.96
0.94
0.92
–50 –25
EN RISING
EN FALLING
0 25 50 75 100 125 150
TEMPERATURE (°C)
8616 G09
8616f
5
5 Page 
LT8616
Operation
Foreword
The LT8616 is a dual monolithic step down regulator. The
two channels differ in maximum current and input range.
The following sections describe the operation of channel
1 and common circuits. They will highlight channel 2 dif-
ferences and interactions only when relevant. To simplify
the application, both VIN1 and VIN2 are assumed to be con-
nected to the same input supply. However, note that VIN1
must be greater than 3.4V for either channel to operate.
Operation
The LT8616 is a dual monolithic, constant frequency, peak
current mode step-down DC/DC converter.
An oscillator, with frequency set using a resistor on the RT
pin, turns on the internal top power switch at the beginning
of each clock cycle. Current in the inductor then increases
until the top switch current comparator trips and turns off
the top power switch. The peak inductor current at which
the top switch turns off is controlled by the voltage on the
internal VC node. The error amplifier servos the VC node
by comparing the voltage on the FB pin with an internal
0.790V reference.When the load current increases it causes
a reduction in the feedback voltage relative to the reference,
causing the error amplifier to raise the VC voltage until the
average inductor current matches the new load current.
When the top power switch turns off, the synchronous
power switch turns on until the next clock cycle begins or
inductor current falls to zero. If overload conditions result
in more than the valley current limit flowing through the
bottom switch, the next clock cycle will be delayed until
current returns to a safe level.
If either EN/UV pin is low, the corresponding channel is
shut down. If both EN/UV pins are low, the LT8616 is
fully shut down and draws 1.7µA from the input supply.
When the EN/UV pins are above 1.03V, the corresponding
switching regulators will become active. 1.3μA is supplied
by VIN1 to common bias circuits for both channels.
Each channel can independently enter Burst Mode opera-
tion to optimize efficiency at light load. Between bursts,
all circuitry associated with controlling the output switch
is shut down, reducing the channel's contribution to in-
put supply current. In a typical application, 6.5μA will be
consumed from the input supply when regulating both
channels with no load. Ground the SYNC/MODE pin for
Burst Mode operation or apply a DC voltage above 2.4V
to use pulse-skipping mode. If a clock is applied to the
SYNC/MODE pin, both channels will synchronize to the
external clock frequency and operate in pulse-skipping
mode. While in pulse-skipping mode the oscillator operates
continuously and SW transitions are aligned to the clock.
During light loads, switch pulses are skipped to regulate
the output and the quiescent current per channel will be
several hundred µA.
To improve efficiency across all loads, supply current to
internal circuitry can be sourced from the BIAS pin when
biased at 3.1V or above. Otherwise, the internal circuitry
will draw current exclusively from VIN1. The BIAS pin
should be connected to the lowest VOUT programmed at
3.3V or above.
Comparators monitoring the FB pin voltage will pull the
corresponding PG pin low if the output voltage varies
more than ±10% (typical) from the regulation voltage or
if a fault condition is present.
Tracking soft-start is implemented by providing constant
current via the TR/SS pin to an external soft-start capaci-
tor to generate a voltage ramp. FB voltage is regulated to
the voltage at the TR/SS pin until it exceeds 0.790V; FB
is then regulated to the 0.790V reference. Soft-start also
reduces the valley current limit to avoid inrush current
during start-up. The SS capacitor is reset during shutdown,
VIN1 undervoltage, or thermal shutdown.
Channel 1 is designed for 1.5A load, whereas channel 2
is designed for 2.5A load. Channel 1 has a minimum VIN1
requirement of 3.4V, but channel 2 can operate with no
minimum VIN2 provided that the minimum VIN1 has been
satisfied.
For more information www.linear.com/LT8616
8616f
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11 Page | ||
| Páginas | Total 24 Páginas | |
| PDF Descargar | [ Datasheet LT8616.PDF ] | |
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