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LTC3829IUHF#TRPBF

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P24P25-P27P28-P30P31-P33P34-P36P37-P39P40-P40
LTC3829
10
3829fc
For more information www.linear.com/LTC3829
FUNCTIONAL DIAGRAM
–
+
–
++
SLEEP
ISET
INTV
CC
0.55V
–
+
–
+
0.5V
SS
–
+
1.22V
RUN
ISET
1.25µA
V
IN
EA
I
TH
R
C
C
C1
C
SS
ISET
ISET
RUN TK/SS
0.6V
REF
S
R
Q
SHED
COMP
5V
REG
IFAST
SLOPE RECOVERY
ACTIVE CLAMP
OSC
MODE/SYNC
DETECT
SLOPE
COMPENSATION
UVLO
1
51k
I
THB
1.0µA
IFAST
CLKOUT
FREQ
MODE PLLIN
ITEMP
0.6V
BURSTEN
EXTV
CC
I
LIM
–
+
–
+
I
COMP
I
REV
F
–
+
4.7V
F
3k
–
+
–
+
OV
UV
–
+
–
–
+
+
–
+
DIFFAMP
0.54V
V
FB
PGOOD
PGND
C
VCC
C
B
M1
M2
V
OUT
L1
INTV
CC
V
IN
C
OUT
D
B
BG
SENSE
–
SENSE
+
SW
TG
BOOST
INTV
CC
DIFFOUT
DIFFN
3829 BD
SENSE1
+
SENSE1
–
SENSE2
+
SENSE2
–
SENSE3
+
SENSE3
–
DIFFP
SGND
AVP
0.66V
R1
R
PRE-AVP
40k 40k
40k
R
AVP
40k
R2
SWITCH
LOGIC
AND
ANTISHOOT-
THROUGH
OV
RUN
ON
FCNT
PLL-SYNC
TEMPSNS
+
C
IN
+
V
IN
LTC3829
11
3829fc
For more information www.linear.com/LTC3829
OPERATION
Main Control Loop
The LTC3829 uses a constant frequency, current mode
step-down architecture. During normal operation, each
top MOSFET is turned on each cycle when the oscillator
sets the RS latch, and turned off when the main current
comparator, I
CMP
, resets each RS latch. The peak inductor
current at which I
CMP
resets the RS latch is controlled by
the voltage on the I
TH
pin, which is the output of the er-
ror amplifier, EA. The remote sense amplifier (DIFFAMP)
produces
a signal equal to the differential voltage sensed
across the output capacitor and re-references it to the lo
-
cal IC ground reference. The V
FB
pin receives a portion of
this feedback signal and compares it to the internal 0.6V
reference. When the load current increases, it causes a
slight decrease in the V
FB
pin voltage relative to the 0.6V
reference, which in turn causes the I
TH
voltage to increase
until each inductor’s average current equals one-third of
the new load current (assuming all three current sensing
resistors are equal). After each top MOSFET has turned off,
the bottom MOSFET is turned on until either the inductor
current starts to reverse, as
indicated by the reverse cur-
rent
comparator,
I
REV
, or the beginning of the next cycle.
The main control loop is shut down by pulling the RUN
pin low. Releasing RUN allows an internal 1.0µA current
source to pull up the RUN pin. When the RUN pin reaches
1.22V, the main control loop is enabled and the IC is
powered up. When the RUN pin is low, all functions are
kept in a controlled state.
INTV
CC
/EXTV
CC
Power
Power for the top and bottom MOSFET drivers and most
other internal circuitry is derived from the INTV
CC
pin.
When the EXTV
CC
pin is left open or tied to a voltage less
than 4.7V, an internal 5V linear regulator supplies INTV
CC
power from V
IN
. If EXTV
CC
is taken above 4.7V, the 5V
regulator is turned off and an internal switch is turned on
connecting EXTV
CC
. Using the EXTV
CC
pin allows the INTV
CC
power to be derived from a high efficiency external source
such as a switching regulator output. Each top MOSFET
driver is biased from the floating bootstrap capacitor, C
B
,
which normally recharges during each off cycle through
an external diode when the top MOSFET turns off
. If the
input
voltage, V
IN
, decreases to a voltage close to V
OUT
,
the loop may enter dropout and attempt to turn on the
top MOSFET continuously. The dropout detector detects
this and forces the top MOSFET off for about one-twelfth
of the clock period plus 100ns every third cycle to allow
C
B
to recharge. However, it is recommended that a load
be present or the IC operates at low frequency during the
dropout transition to ensure C
B
is recharged.
Shutdown and Start-Up (RUN and TK/SS Pins)
The LTC3829 can be shut down using the RUN pin. Pulling
the RUN pin below 1.22V shuts down the main control loop
for the controller and most internal circuits, including the
INTV
CC
regulator. Releasing the RUN pin allows an internal
1.0µA current to pull up the pin and enable the controller.
Alternatively, the RUN pin may be externally pulled up or
driven directly by logic. Be careful not to exceed the ab
-
solute maximum
rating of 6V on this pin. The start-up of
the controller’s output voltage, V
OUT
, is controlled by the
voltage on the TK/SS pin. When the voltage on the TK/SS
pin
is less than the 0.6V internal reference, the LTC3829
regulates the V
FB
voltage to the TK/SS pin voltage instead
of the 0.6V reference. This allows the TK/SS pin to be used
to program a soft-start by connecting an external capacitor
from the TK/SS pin to SGND. An internal 1.25µA pull-up
current charges this capacitor, creating a voltage ramp on
the TK/SS pin. As the TK/SS voltage rises linearly from
0V to 0.6V (and beyond), the output voltage, V
OUT
, rises
smoothly from zero to its final value. Alternatively, the TK/
SS pin can be used to cause the start-up of V
OUT
to track
that of another supply. Typically, this requires connect-
ing 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 INTV
CC
drops below its undervoltage
lockout threshold of 3.3V, the TK/SS pin is pulled low
by an internal MOSFET. When in undervoltage lockout,
all phases of the controller are disabled and the external
MOSFETs are held off.
(Refer to Functional Diagram)
LTC3829
12
3829fc
For more information www.linear.com/LTC3829
Light Load Current Operation (Burst Mode Operation,
Stage Shedding or Continuous Conduction)
The LTC3829 can be enabled to enter high efficiency
Burst Mode operation, Stage Shedding mode or forced
continuous conduction mode. To select forced continuous
operation, tie the MODE pin to a DC voltage below 0.6V
(e.g., SGND). To select Stage Shedding mode of opera-
tion, tie the MODE pin to INTV
CC
. To select Burst Mode
operation, float the MODE pin.
When the controller is enabled for Burst Mode operation,
the peak current in the inductor is set to approximately
one-sixth of the maximum sense voltage even though the
voltage on the I
TH
pin indicates a lower value. The peak
current can be programmed through the ISET pin. If the
average inductor current is higher than the load current,
the error amplifier, EA, will decrease the voltage on the
I
TH
pin. When the I
TH
voltage drops below 0.5V (can
also be programmed by the ISET pin), the internal sleep
signal goes high (enabling sleep mode) and the 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 a controller is enabled for Burst Mode operation,
the inductor current is not allowed to reverse. The reverse
current comparator, I
REV
, turns off the bottom external
MOSFET just before the inductor current reaches zero,
preventing it from reversing 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 I
TH
pin. 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 pin is connected to INTV
CC
, the LTC3829
operates in Stage Shedding mode at light loads. The
controller will turn off channels 2 and 3 and increase
the current gain of the first channel to ensure smooth
transition. The threshold where the controller goes into
Stage Shedding mode is when the
I
TH
voltage drops
below 0.5V, but it can be programmed by ISET pin. The
inductor current is not allowed to reverse in this mode
(discontinuous operation). At very light loads, the cur
-
rent comparator
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). This mode
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.
2-Chip Operations (CLKOUT Pin)
The LTC3829’s three channels are 120° out of phase
providing multiphase operation. This configuration can
provide enough power for most high current applications.
However, for even higher power applications, the LTC3829
can be configured for PolyPhase
®
and 2-chip operation.
The LTC3829 features a CLKOUT pin which enables two
LTC3829s to operate out of phase. The CLKOUT signal is
60° out of phase with respect to phase 1 of the controller.
In Stage Shedding mode, however, the CLKOUT signal is
180° out of phase with respect to phase 1 of the controller.
Frequency Selection and
Phase-Locked Loop
(FREQ and 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 PLLIN pin is not being driven by an external clock
source, the FREQ pin can be used to program the control
-
ler’s operating
frequency from 250kHz to 770kHz. There
is a precision 10µA current flowing out of the FREQ pin
so that the user can program the controller’s switching
frequency with a single resistor to SGND. A curve is pro
-
vided later in
the Applications Information section showing
the relationship between the voltage on the FREQ pin and
switching frequency.
OPERATION
(Refer to Functional Diagram)
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LTC3829IUHF#TRPBF

Mfr. #:
Buy LTC3829IUHF#TRPBF
Manufacturer:
Analog Devices / Linear Technology
Description:
Switching Voltage Regulators 3-Phase, Synchronous Regulators with Diffamp
Lifecycle:
New from this manufacturer.
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