LTC3459 LINER [Linear Technology], LTC3459 Datasheet - Page 7

• Manufacturer Part Number: LTC3459
• Description: 10V Micropower Synchronous Boost Converter in ThinSOT
• Manufacturer: LINER [Linear Technology]

OPERATIO
Operation
The LTC3459 synchronous boost converter utilizes a Burst
Mode control technique to achieve high efficiency over a
wide dynamic range. A 2.5% accurate comparator is used
to monitor the output voltage (V
comparator threshold no switching occurs and only qui-
escent current (10 A) is drawn from the power source.
When V
ing commences and the output capacitor is charged. Dur-
ing the on time of the switching period, inductor current is
ramped through an internal N-channel MOSFET to GND
until a peak current (75mA) is detected. A P-channel
MOSFET connects the inductor to V
delivering energy to the load. The off time is controlled by
an internal timer which is proportional to 1/(V
Anticross conduction circuitry ensures the N- and
P-channel switches are never on simultaneously.
Only three power components and two feedback resistors
are required to complete the design of the boost converter,
an external Schottky diode is not required. The high
operating frequency allows the use of low value, low
profile inductors and tiny external ceramic capacitors. The
OUT
110
100
90
70
60
50
80
drops below the comparator threshold, switch-
1.5
Figure 2. Typical I
2
U
2.5
RIPPLE
I
3
V
PEAK
OUT
AC
V
IN
3.5
(V)
15 H
22 H
33 H
PEAK
4
OUT
N
OUT
4.5
Figure 1. Inductor Current and V
), if V
Values
t
OFF
P
BURST ON
during the off time
5
N
3459 F02
OUT
t
OFF
P
5.5
is above the
N
OUT
t
OFF
P
– V
N
IN
).
I
ZERO
P
WAIT
boost converter disconnects V
down to avoid loading the input power source.
Peak Current Overshoot
The LTC3459’s peak current comparator has a delay of
approximately 100ns from the time inductor current
reaches current limit until the internal N-channel MOSFET
turns off. This delay causes the peak current to overshoot
based on the inductor value and V
based on a 65mA initial I
t
The LTC3459’s t
current continuous during a Burst Mode switching packet,
thereby increasing current capability at the output. A
larger inductor value will have lower peak to peak current
ripple, increasing the available current to the load. This
improvement is offset somewhat by the reduced I
OFF
OUT
I
PEAK
Timer
Ripple Waveforms
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
I
~50mV
LIMIT
SLEEP
0
0.5
P-P
OFF
1.5
Figure 3. t
timer is designed to keep the inductor
100
2.5
~100mA
V
3.5
ns
OUT
LIMIT
N
BURST ON
4.5
– V
V
OFF
L
t
IN
OFF
IN
P
).
OUT
3459 F01
(V)
5.5
Times
N
IN
6.5
from V
as follows (Figure 2 is
7.5
LTC3459
3459 F03
IN
8.5
during shut-
PEAK
7
3459f