LTC3787MPGN 查看數據表（PDF） - Linear Technology
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LTC3787MPGN Datasheet PDF : 36 Pages
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LTC3787
BLOCK DIAGRAM
PHASMD
CLKOUT
FREQ
20μA
CLK2
VCO CLK1
PFD
PLLIN/
MODE
100k
ILIM
VBIAS
EXTVCC
5.4V
LDO
EN
+
4.8V –
SYNC
DET
CURRENT
LIMIT
5.4V
LDO
EN
INTVCC
SHDN
–+
3.8V
SGND
DUPLICATE FOR SECOND CONTROLLER CHANNEL
S
Q
R
SHDN
SWITCHING
LOGIC
AND
CHARGE
PUMP
BOOST
TG
SW
INTVCC
BG
INTVCC
DB
CB
0.425V +
–
SLEEP
PGND
ICMP
–+
2.8V
0.7V
SLOPE COMP
+
IREV
+– –
2mV
SENSE –
SENSE+
L
RSENSE
SENS LO
2.5V
VFB
EA
1.2V
SS
VOUT
COUT
VIN
CIN
0.5μA/
4.5μA
11V
SHDN
RUN
SENS
LO
OV
1.32V
ITH
10μA 1.32V +
–
VFB
SS
+
1.08V –
CSS
PGOOD
CC
CC2
RC
3787 BD
OPERATION
Main Control Loop
The LTC3787 uses a constant-frequency, current mode
step-up architecture with the two controller channels
operating out of phase. During normal operation, each
external bottom MOSFET is turned on when the clock for
that channel sets the RS latch, and is turned off when the
main current comparator, ICMP, resets the RS latch. The
peak inductor current at which ICMP trips and resets the
latch is controlled by the voltage on the ITH pin, which is
the output of the error amplifier EA. The error amplifier
compares the output voltage feedback signal at the VFB
pin (which is generated with an external resistor divider
connected across the output voltage, VOUT, to ground), to
the internal 1.200V reference voltage. In a boost converter,
the required inductor current is determined by the load
current, VIN and VOUT. When the load current increases,
it causes a slight decrease in VFB relative to the reference,
which causes the EA to increase the ITH voltage until the
average inductor current in each channel matches the new
requirement based on the new load current.
After the bottom MOSFET is turned off each cycle, the
top MOSFET is turned on until either the inductor current
starts to reverse, as indicated by the current comparator,
IR, or the beginning of the next clock cycle.
3787fc
11
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