LTM4609 LINER [Linear Technology], LTM4609 Datasheet - Page 9

• Manufacturer Part Number: LTM4609
• Description: 36VIN, 34VOUT High Effi ciency Buck-Boost DC/DC ?Module
• Manufacturer: LINER [Linear Technology]

OPERATION
APPLICATIONS INFORMATION
Power Module Description
The LTM4609 is a non-isolated buck-boost DC/DC power
supply. It can deliver a wide range output voltage from
0.8V to 34V over a wide input range from 4.5V to 36V,
by only adding the sensing resistor, inductor and some
external input and output capacitors. It provides precisely
regulated output voltage programmable via one external
resistor. The typical application schematic is shown in
Figure 18.
The LTM4609 has an integrated current mode buck-boost
control, ultralow R
and integrated Schottky diodes. With current mode control
and internal feedback loop compensation, the LTM4609
module has suffi cient stability margins and good transient
performance under a wide range of operating conditions
and with a wide range of output capacitors. The frequency
of LTM4609 can be operated from 200kHz to 400kHz by
setting the voltage on the PLLFLTR pin. Alternatively, its
The typical LTM4609 application circuit is shown in
Figure 18. External component selection is primarily
determined by the maximum load current and output
voltage. Refer to Table 3 for specifi c external capacitor
requirements for a particular application.
Output Voltage Programming
The PWM controller has an internal 0.8V±1% reference
voltage. As shown in the Block Diagram, a 100k 0.5%
internal feedback resistor connects V
together. Adding a resistor R
SGND pin programs the output voltage:
Table 1. R
V
V
R
R
OUT
OUT
FB
FB
V
OUT
8.66k 7.15k 5.62k
Open
0.8V
10V
= 0.8V •
FB
Resistor (0.5%) vs Output Voltage
115k
1.5V
12V
100k + R
DS(ON)
47.5k
2.5V
15V
R
FB
FETs with fast switching speed
32.4k 19.1k
5.23k 4.12k
3.3V
16V
FB
FB
from the V
20V
5V
15.4k
OUT
3.4k
24V
6V
and V
FB
2.74k 2.37k
11k
30V
8V
pin to the
FB
9.76k
34V
pins
9V
frequency can be synchronized by the input clock signal
from the PLLIN pin. The typical switching frequency is
400kHz.
The Burst Mode
be enabled at light loads in the LTM4609 to improve its
effi ciency, while the forced continuous mode and discon-
tinuous mode operations are used for constant frequency
applications. Foldback current limiting is activated in an
overcurrent condition as V
and undervoltage comparators pull the open-drain PGOOD
output low if the output feedback voltage exits the ±7.5%
window around the regulation point. Pulling the RUN pin
below 1.6V forces the controller into its shutdown state.
If an external bias supply is applied on the EXTV
an effi ciency improvement will occur due to the reduced
power loss in the internal linear regulator. This is especially
true at the higher input voltage range.
Burst Mode is a registered trademark of Linear Technology Corporation.
Operation Frequency Selection
The LTM4609 uses current mode control architecture at
constant switching frequency, which is determined by the
internal oscillator’s capacitor. This internal capacitor is
charged by a fi xed current plus an additional current that
is proportional to the voltage applied to the PLLFLTR pin.
The PLLFLTR pin can be grounded to lower the frequency
to 200kHz or tied to 2.4V to yield approximately 400kHz.
When PLLIN is left open, the PLLFLTR pin goes low, forc-
ing the oscillator to its minimum frequency.
A graph for the voltage applied to the PLLFLTR pin vs
frequency is given in Figure 2. As the operating frequency
increases, the gate charge losses will be higher, thus the
effi ciency is low. The maximum switching frequency is
approximately 400kHz.
FREQUENCY SYNCHRONIZATION
The LTM4609 can also be synchronized to an external
source via the PLLIN pin instead of adjusting the voltage on
the PLLFLTR pin directly. The power module has a phase-
®
and skip-cycle mode operations can
FB
drops. Internal overvoltage
LTM4609
CC
pin, then
4609fa
9