ltc3787gn Linear Technology Corporation, ltc3787gn Datasheet - Page 11

• Manufacturer Part Number: ltc3787gn
• Description: Ltc3787 - Polyphase Synchronous Boost Controller
• Manufacturer: Linear Technology Corporation

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
block DiagraM
PHASMD
4.8V
EXTV
PLLIN/
VBIAS
MODE
FREQ
ILIM
CC
+
–
100k
EN
5.4V
LDO
20µA
CURRENT
LIMIT
EN
5.4V
LDO
SYNC
DET
INTV
CC
VCO
PFD
CLKOUT
CLK2
CLK1
SHDN
–
SGND
3.8V
+
RUN
SHDN
0.5µA/
4.5µA
SLOPE COMP
2.8V
0.7V
11V
SENS LO
DUPLICATE FOR SECOND CONTROLLER CHANNEL
SENS
LO
I
CMP
0.425V
–
+
–
connected across the output voltage, V
the internal 1.200V reference voltage. In a boost converter,
the required inductor current is determined by the load
current, V
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.
+
S
R
+
–
+
–
10µA
SS
Q
2.5V
2mV
SHDN
+ –
SLEEP
1.32V
1.08V
VFB
C
SS
IN
+
–
I
REV
and V
+
+
–
–
SWITCHING
OV
CHARGE
LOGIC
EA
PUMP
AND
–
–
+
+
–
OUT
1.2V
SS
1.32V
. When the load current increases,
INTV
CC
SENSE
SENSE
BOOST
PGOOD
SW
VFB
ITH
TG
BG
–
+
INTV
PGND
L
R
CC
OUT
D
SENSE
C
C
LTC3787
B
C2
B
C
C
, to ground), to
3787 BD
R
V
C
C
IN
IN
11
V
OUT
C
3787fa
OUT