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PDF LTC3774 Data sheet ( Hoja de datos )
| Número de pieza | LTC3774 | |
| Descripción | Multiphase Current Mode Synchronous Controller | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LTC3774
Dual, Multiphase Current
Mode Synchronous Controller
for Sub-Milliohm DCR Sensing
FEATURES
DESCRIPTION
n Sub-Milliohm DCR Current Sensing
n Operates with Power Blocks, DRMOS or External
Gate Drivers and MOSFETs
n Supports Phase Shedding and N+1 Phase
Redundancy
n Programmable DCR Temperature Compensation
n ±0.75% Maximum Total DC Output Error Over
Temperature
n Dual Differential Remote Output Voltage Sense
Amplifiers
n Phase-Lockable Fixed Frequency Range: 200kHz to
1.2MHz
n VIN Range: 4.5V to 38V
n VOUT Range: 0.6V to 3.5V
n Supports Smooth Start-Up into Pre-Biased Outputs
n Programmable Soft-Start or VOUT Tracking
n Hiccup Mode/Soft Recovery from Output Overcurrent
n 36-Lead (5mm × 6mm) QFN Package
APPLICATIONS
n Computer Systems
n Telecom and Datacom Systems
n Industrial Equipment
n DC Power Distribution Systems
The LTC®3774 is a dual PolyPhase® current mode syn-
chronous step-down switching regulator controller that
drives power blocks, DRMOS or external gate drivers and
power MOSFETs. It offers an LTC-proprietary technique
that enhances the signal-to-noise ratio of the current
sense signal, allowing the use of inductors with very low
DC winding resistances as the current sense element for
maximum efficiency and reduced jitter.
The maximum current sense voltage is programmable
from 10mV to 30mV. High speed, low offset remote sense
differential amplifiers and a precise 0.6V reference provide
accurate output voltages between 0.6V and 3.5V from a wide
4.5V to 38V input supply range. Soft recovery from output
shorts or overcurrent minimizes output overshoot. Burst
Mode® operation, continuous and pulse-skipping modes
are supported. The constant operating frequency can be
synchronized to an external clock or linearly programmed
from 200kHz to 1.2MHz. Up to six LTC3774 controllers can
be paralleled for 1-, 2-, 3-, 4-, 6-, 8- or 12-phase operation.
The LTC3774 is available in a 36-lead (5mm × 6mm) QFN
package.
L, LT, LTC, LTM, Linear Technology, the Linear logo, PolyPhase and Burst Mode are registered
trademarks and No RSENSE and Hot Swap are trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners. Protected by U.S. Patents,
including 5481178, 5705919, 5929620, 6177787, 6580258, 6498466, 6611131, patent pending.
TYPICAL APPLICATION
High Efficiency Dual Phase 1.5V/60A Step-Down Converter
0.33µH
(0.32mΩ DCR)
1/4 INTVCC
DRMOS
300µF +
4V
15k
10k 2200pF
15k
RUN1, 2
ILIM1, 2
HIZB1
HIZB2
PWM1
PWMEN1
VOSNS1–
SNSA1+
SNS1–
SNSD1+
VOSNS1+
ITH1
TK/SS1
VIN
LTC3774
TK/SS2
PHSMD
CLKOUT
PGOOD1,2
MODE/PLLIN
PWM2
PWMEN2
GND
VOSNS2–
SNSA2+
SNS2–
SNSD2+
FREQ
VOSNS2+
ITH2
INTVCC
0.1µF
4.7µF
fIN
500kHz
37.5k
DRMOS
22µF
50V
VIN
4.5V TO 20V
0.33µH
(0.32mΩ DCR)
330µF +
4V
VOUT
1.5V
60A
3774 TA01a
For more information www.linear.com/LTC3774
3774f
1
1 page  
LTC3774
TYPICAL PERFORMANCE CHARACTERISTICS
Maximum Current Sense Threshold
vs Common Mode Voltage
35
30
25
20
15
10
5
INTVCC
3/4 INTVCC
1/4 INTVCC
0
1/2 INTVCC
0
0 0.5 1 1.5 2 2.5 3 3.5
COMMON MODE VOLTAGE (V)
3774 G01
Maximum Current Sense
Threshold vs Feedback Voltage
(Current Foldback)
35
30 ILIM = INTVCC
ILIM = 3/4 INTVCC
25
ILIM = 1/2 INTVCC
20
15 ILIM = 1/4 INTVCC
10 ILIM = 0
5
0
0 0.1 0.2 0.3 0.4 0.5 0.6
FEEDBACK VOLTAGE (V)
3774 G02
Input Quiescent Current
vs Input Voltage
12
Shutdown Current
vs Input Voltage
60
Current Sense Threshold
vs ITH Voltage
35
30
25
IIIIILLLLLIIIIIMMMMM
=
=
=
=
=
0
113IN///424TVIIINNNCTTTCVVVCCCCCC
20
15
10
5
0
–5
–10
0
0.25 0.5 0.75 1 1.25 1.5 1.75 2
V(ITH) (V)
3774 G03
INTVCC Line Regulation
6
10 50
5
8 40
4
6 30
3
4 20
2
2 10
1
0
0 5 10 15 20 25 30 35 40
INPUT VOLTAGE (V)
3774 G04
Oscillator Frequency
vs Input Voltage
1200
1000
75kΩ
800
600 47.5kΩ
400
200 23.2kΩ
0
0 5 10 15 20 25 30 35 40
INPUT VOLTAGE (V)
3774 G05
0
0 5 10 15 20 25 30 35 40
INPUT VOLTAGE (V)
3774 G06
Load Step (Continuous
Conduction Mode)
VIN = 12V
VOUT = 1.5V
50mV/DIV
AC-COUPLED
ILOAD
5A-DIV
15A TO 30A
50µs/DIV
3774 G08
0
0 5 10 15 20 25 30 35 40
INPUT VOLTAGE (V)
3774 G07
For more information www.linear.com/LTC3774
3774f
5
5 Page 
LTC3774
OPERATION
used to cause the start-up of VOUT to track that of another
supply. Typically, this requires connecting to the TK/SS
pin an external resistor divider from the other supply to
ground (see the Applications Information section). When
the RUN pin is pulled low to disable the controller, or when
INTVCC drops below its undervoltage lockout threshold of
3.75V, the TK/SS pin is pulled low by an internal MOSFET.
When in undervoltage lockout, the controller is disabled
and the external MOSFETs are held off.
Light Load Current Operation (Burst Mode Operation,
Pulse-Skipping or Continuous Conduction)
The LTC3774 can be enabled to enter high efficiency Burst
Mode operation, constant-frequency pulse-skipping mode
or forced continuous conduction mode. To select forced
continuous operation, tie the MODE pin to GND. To select
pulse-skipping mode of operation, tie the MODE/PLLIN
pin to INTVCC. To select Burst Mode operation, float the
MODE/PLLIN pin. When the controller is enabled for Burst
Mode operation, the peak current in the inductor is set to
approximately one-third of the maximum sense voltage
even though the voltage on the ITH pin indicates a lower
value. If the average inductor current is higher than the
load current, the error amplifier, EA, will decrease the
voltage on the ITH pin. When the ITH voltage drops below
0.5V, the internal sleep signal goes high (enabling “sleep”
mode) and both external MOSFETs are turned off.
In sleep mode, the load current is supplied by the output
capacitor. As the output voltage decreases, the EA’s output
begins to rise. When the output voltage drops enough, the
sleep signal goes low, and the controller resumes normal
operation by turning on the top external MOSFET on the
next cycle of the internal oscillator. When the controller
is enabled for Burst Mode operation, the inductor current
is not allowed to reverse. The reverse current comparator
(IREV) turns off the bottom external MOSFET just before
the inductor current reaches zero, preventing it from re-
versing and going negative. Thus, the controller operates
in discontinuous operation.
In forced continuous operation, the inductor current is
allowed to reverse at light loads or under large transient
conditions. The peak inductor current is determined by
the voltage on the ITH pin, just as in normal operation. In
this mode, the efficiency at light loads is lower than in
Burst Mode operation. However, continuous mode has the
advantages of lower output ripple and less interference
with audio circuitry.
When the MODE/PLLIN pin is connected to INTVCC, the
LTC3774 operates in PWM pulse skipping mode at light
loads. At very light loads, the current comparator, ICMP ,
may remain tripped for several cycles and force the external
top MOSFET to stay off for the same number of cycles (i.e.,
skipping pulses). The inductor current is not allowed to
reverse (discontinuous operation). This mode, like forced
continuous operation, exhibits low output ripple as well as
low audio noise and reduced RF interference as compared
to Burst Mode operation. It provides higher low current
efficiency than forced continuous mode, but not nearly as
high as Burst Mode operation.
Frequency Selection and Phase-Locked Loop
(FREQ and MODE/PLLIN Pins)
The selection of switching frequency is a trade-off between
efficiency and component size. Low frequency opera-
tion increases efficiency by reducing MOSFET switching
losses, but requires larger inductance and/or capacitance
to maintain low output ripple voltage.
If the MODE/PLLIN pin is not being driven by an external
clock source, the FREQ pin can be used to program the
controller’s operating frequency from 200kHz to 1.2MHz.
There is a precision 20µA current flowing out of the FREQ
pin so that the user can program the controller’s switching
frequency with a single resistor to GND. A curve is provided
later in the Applications Information section showing the
relationship between the voltage on the FREQ pin and
switching frequency.
A phase-locked loop (PLL) is available on the LTC3774
to synchronize the internal oscillator to an external clock
source that is connected to the MODE/PLLIN pin. The PLL
loop filter network is integrated inside the LTC3774. The
phase‑locked loop is capable of locking any frequency
within the range of 200kHz to 1.2MHz. The frequency setting
resistor should always be present to set the controller’s
initial switching frequency before locking to the external
clock. The controller operates in forced continuous mode
when it is synchronized.
For more information www.linear.com/LTC3774
3774f
11
11 Page | ||
| Páginas | Total 30 Páginas | |
| PDF Descargar | [ Datasheet LTC3774.PDF ] | |
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