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PDF LT8610AC-1 Data sheet ( Hoja de datos )
| Número de pieza | LT8610AC-1 | |
| Descripción | 3.5A Synchronous Step-Down Regulator | |
| Fabricantes | Linear | |
| Logotipo |  |
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Features
n LT8610 Feature Set, Plus:
3V Minimum Input Voltage
800mV Feedback Voltage
3.5A Maximum Output Current
Fast 30ns Minimum Switch-On Time
Improved Burst Mode Efficiency
Improved EMI
n Wide Input Voltage Range: 3V to 42V
n Ultralow Quiescent Current Burst Mode® Operation:
2.5μA IQ Regulating 12VIN to 3.3VOUT
n High Efficiency Synchronous Operation:
95% Efficiency at 1A, 5VOUT from 12VIN
93% Efficiency at 1A, 3.3VOUT from 12VIN
n Low Dropout Under All Conditions: 200mV at 1A
n Safely Tolerates Inductor Saturation in Overload
n Adjustable and Synchronizable Frequency:
LT8610AC: 200kHz to 2.2MHz
LT8610AC-1: 1.5MHz to 2.2MHz
n Accurate 1.015V Enable Pin Threshold
n Output Soft-Start and Tracking
n Small Thermally Enhanced 16-Lead MSOP Package
Applications
n Automotive and Industrial Supplies
n GSM Power Supplies
LT8610AC/LT8610AC-1
42V, 3.5A Synchronous
Step-Down Regulator with
2.5µA Quiescent Current
Description
The LT®8610AC/LT8610AC-1 is a compact, high efficiency,
high speed synchronous monolithic step-down switching
regulator that consumes only 2.5µA of quiescent current.
Compared to the LT8610AB, the LT8610AC/LT8610AC-1
has a lower feedback voltage of 800mV and a lower mini-
mum VIN of 3V. The LT8610AC/LT8610AC-1 has the same
additional features of the LT8610AB as compared to the
LT8610: higher maximum output current of 3.5A, faster
minimum on time of 30ns, and higher light load efficiency.
The LT8610AC/LT8610AC-1 has a SYNC pin for syn-
chronization to an external clock. A capacitor on the TR/
SS pin programs the output voltage ramp rate during
startup. The PG flag signals when VOUT is within ±8% of
the programmed output voltage as well as fault conditions.
The LT8610AC-1 has internal compensation optimized for
high switching frequencies resulting in improved transient
response compared to the LT8610AC. The LT8610AC-1
also has a feature which will soft-start the part when
exiting dropout or brownout conditions reducing output
voltage overshoot.
LT8610AC
FEEDBACK
OUTPUT MIN ON IMPROVED
VOLTAGE MIN VIN CURRENT TIME
EMI
0.80V 3.0V 3.5A 30ns
Yes
LT8610AB* 0.97V 3.4V 3.5A 30ns
Yes
LT8610A*
0.97V
3.4V
3.5A 30ns
Yes
LT8610*
0.97V 3.4V 2.5A 50ns
–
*See LT8610A/LT8610AB or LT8610 data sheet.
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 3.5A Step-Down Converter
VIN
5.5V TO 42V
4.7µF
10nF
1µF
VIN BST
EN/UV
PG LT8610AC SW
SYNC
BIAS
TR/SS
FB
INTVCC
RT
GND
60.4k
0.1µF
4.7µH
1M
10pF
191k
fSW = 700kHz
8610ac1 TA01a
VOUT
5V
47µF 3.5A
×2
100
90
80
70
60
50
40
30
0.1
Efficiency at 5VOUT
VIN = 12V
VIN = 24V
VIN = 36V
1 10 100
LOAD CURRENT (mA)
1000
8610ac1 TA01b
For more information www.linear.com/LT8610AC
8610acfa
1
1 page  
LT8610AC/LT8610AC-1
Typical Performance Characteristics TA = 25°C, unless otherwise noted.
No Load Supply Current
5.0
4.5
VOUT = 3.3V
IN REGULATION
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
0 5 10 15 20 25 30 35 40 45
INPUT VOLTAGE (V)
8610ac1 G10
No Load Supply Current
25
VOUT = 3.3V
VIN = 12V
20 IN REGULATION
15
10
5
0
–55 –25
5 35 65 95
TEMPERATURE (°C)
125 155
8610ac1 G11
Top FET Current Limit vs Duty Cycle
8.0
7.5
7.0
6.5
6.0
5.5
5.0
4.5
4.0
3.5
3.0
0
0.2 0.4 0.6 0.8 1.0
DUTY CYCLE
8610ac1 G12
Top FET Current Limit
7.00
6.75
6.50
6.25 30% DC
6.00
5.75
5.50
5.25
5.00
4.75
4.50
–55 –25
5
35 65
TEMPERATURE (°C)
95 125
8610ac1 G13
Bottom FET Current Limit
5.50
5.25
5.00
4.75
4.50
4.25
4.00
3.75
3.50
3.25
3.00
–55 –25
5 35 65 95
TEMPERATURE (°C)
125 155
8610ac1 G14
Switch Drop
250
SWITCH CURRENT = 1A
200
150
TOP SW
100
BOT SW
50
0
–55 –25
5 35 65 95
TEMPERATURE (°C)
125 155
8610ac1 G15
Switch Drop
450
400
350
300
250
TOP SW
200
BOT SW
150
100
50
0
0 0.5 1 1.5 2 2.5 3
SWITCH CURRENT (A)
8610ac1 G16
Minimum On-Time
45 ILOAD = 1.5A
43 VSYNC = 5V
41
39
37
35
33
31
29
27
25
–55 –25
VOUT = 3.3V
VOUT = 0.8V
5 35 65 95
TEMPERATURE (°C)
125 155
8610ac1 G17
Minimum Off-Time
125
120
VOUT = 3.3V
ILOAD = 0.5A
115
110
105
100
95
90
85
80
75
–50 –25
5 35 65 95
TEMPERATURE (°C)
125 155
8610ac1 G18
For more information www.linear.com/LT8610AC
8610acfa
5
5 Page 
LT8610AC/LT8610AC-1
Operation
The LT8610AC/LT8610AC-1 is a monolithic, constant
frequency, 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 VFB pin with an internal
0.8V reference. When the load current increases it causes
a reduction in the feedback voltage relative to the reference
leading 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 4.3A flowing through the bottom switch, the
next clock cycle will be delayed until switch current returns
to a safe level.
If the EN/UV pin is low, the LT8610AC/LT8610AC-1 is shut
down and draws 1µA from the input. When the EN/UV pin
is above 1.015V, the switching regulator will become active.
To optimize efficiency at light loads, the LT8610AC/
LT8610AC-1 operates in Burst Mode operation in light
load situations. Between bursts, all circuitry associated
with controlling the output switch is shut down, reducing
the input supply current to 1.7μA. In a typical application,
2.5μA will be consumed from the input supply when
regulating with no load. The SYNC pin is tied low to use
Burst Mode operation and can be tied to a logic high to use
pulse-skipping mode. If a clock is applied to the SYNC pin
the part will synchronize to an external clock frequency and
operate in pulse-skipping mode. While in pulse-skipping
mode the oscillator operates continuously and positive
SW transitions are aligned to the clock. During light loads,
switch pulses are skipped to regulate the output and the
quiescent current 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 3.3V or above. Else, theinternal circuitry will draw
current from VIN. The BIAS pin should be connected to
VOUT if the LT8610AC/LT8610AC-1 output is programmed
at 3.3V or above.
Comparators monitoring the FB pin voltage will pull the
PG pin low if the output voltage varies more than ±8%
(typical) from the set point, or if a fault condition is present.
The oscillator reduces the LT8610AC/LT8610AC-1’s oper-
ating frequency when the voltage at the FB pin is low. This
frequency foldback helps to control the inductor current
when the output voltage is lower than the programmed
value which occurs during start-up or overcurrent condi-
tions. When a clock is applied to the SYNC pin or the SYNC
pin is held DC high, the frequency foldback is disabled
and the switching frequency will slow down only during
overcurrent conditions.
The LT8610AC-1 differs from the LT8610AC in that the
internal compensation is optimized for higher switching
frequency operation and a TR/SS pin discharge circuit is
added to reduce output voltage overshoot when exiting
dropout or brownout conditions. The internal compensa-
tion change increases the bandwidth of the control loop,
which improves transient response. As a consequence
the minimum programmable switching frequency of the
LT8610AC-1 is increased to 1.5MHz. The SS discharge
circuit regulates the TR/SS pin to the same voltage as the
FB pin during dropout or brownout. This feature provides
some soft-starting when the part exits dropout or brownout
which reduces output voltage overshoot. Both of these
changes are intended to reduce output voltage overshoot
in 2MHz switching frequency applications.
For more information www.linear.com/LT8610AC
8610acfa
11
11 Page | ||
| Páginas | Total 26 Páginas | |
| PDF Descargar | [ Datasheet LT8610AC-1.PDF ] | |
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