LT1310 LINER [Linear Technology], LT1310 Datasheet - Page 6

• Manufacturer Part Number: LT1310
• Description: 1.5A Boost DC/DC Converter with Phase-Locked Loop
• Manufacturer: LINER [Linear Technology]

BLOCK DIAGRA
OPERATIO
LT1310
To understand operation, refer to the Block Diagram. The
LT1310 contains a boost switching regulator that can be
phase locked to an external synchronizing signal. The
boost regulator uses current mode control and contains a
1.5A NPN power transistor. This type of control uses two
feedback loops. The main control loop sets output voltage
and operates as follows: a load step causes V
FB voltage to be slightly perturbed. The error amplifier A1
responds to this change in FB by driving the V
higher or lower. Because switch current is proportional to
the V
to be adjusted until V
compensation is taken care of by an RC network from the
V
current limit on a cycle-by-cycle basis. This loop utilizes
current comparator A2 to control peak current. The oscil-
lator issues a set pulse to the flip-flop at the beginning of
each cycle, turning the switch on. With the switch now in
the ON state, the SW pin is effectively connected to
ground. Current ramps up in the inductor linearly at a rate
of V
6
C
pin to ground. Inside this main loop is another that sets
IN
C
/L. Switch current is set by the V
pin voltage, this change causes the switch current
U
1.255V
SHDN
GND
REF
FB
1
2
5
OUT
W
–
+
is once again satisfied. Loop
SHUTDOWN
A1
EXPOSED
PAD
C
pin voltage and
V
10
+
C
OUT
C
A2
pin either
and the
–
RAMP
GEN.
+
+
when the voltage across R
parator, a reset pulse will be generated and the switch will
be turned off. Since the inductor is now loaded up with
current, the SW pin will fly high until it is clamped by the
catch diode, D1. Current will flow through the diode
decreasing at a rate of (V
issues a new set pulse, causing the cycle to repeat.
The LT1310 is phase lockable up to 4.5MHz, giving the
user precise control over switching frequency. The phase
detector compares the incoming sync signal to the internal
oscillator signal. If the switching frequency is lower than
the sync signal, or if the phase lags the sync signal, then
the phase detector output will source current into the
PLL-LPF pin, driving it higher. The PLL-LPF pin is also the
input to the voltage controlled oscillator. If the sync signal
is slower than the switching frequency, the PLL-LPF pin
will sink current until the PLL-LPF pin voltage drops. When
locked, the PLL-LPF pin rests at a voltage between 0V and
1.5V. The PLL-LPF pin is capable of sinking or sourcing
approximately 140 A.
VCO
C
9
T
S
R
5
PLL-LPF
Q
Q
3
DETECTOR
PHASE
OUT
SENSE
0.024
1310 BD
– V
IN
SYNC
trips the current com-
6, 7
SW
)/L until the oscillator
4
1310f