LTC3703IG-5#PBF Linear Technology, LTC3703IG-5#PBF Datasheet - Page 12

• Manufacturer Part Number: LTC3703IG-5#PBF
• Description: IC BUCK/BOOST SYNC ADJ 5A 28SSOP
• Manufacturer: Linear Technology
• Type: Step-Down (Buck), Step-Up (Boost)r

Specifications of LTC3703IG-5#PBF

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 0.8 ~ 55.8 V
• Current - Output: 5A
• Frequency - Switching: 100kHz ~ 600kHz
• Voltage - Input: 9.3 ~ 60 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 28-SSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -

OPERATIO
LTC3703-5
Buck or Boost Mode Operation
The LTC3703-5 has the capability of operating both as a
step-down (buck) and step-up (boost) controller. In boost
mode, output voltages as high as 60V can be tightly
regulated. With the INV pin grounded, the LTC3703-5
operates in buck mode with TG driving the main (top side)
switch and BG driving the synchronous (bottom side)
switch. If the INV pin is pulled above 2V, the LTC3703-5
operates in boost mode with BG driving the main (bottom
side) switch and TG driving the synchronous (top side)
switch. Internal circuit operation is very similar regardless
APPLICATIO S I FOR ATIO
The basic LTC3703-5 application circuit is shown on the first
page of this data sheet. External component selection is de-
termined by the input voltage and load requirements as
explained in the following sections. After the operating
frequency is selected, R
operating frequency and the inductor are chosen for a
desired amount of ripple current and also to optimize ef-
ficiency and component size. Next, the power MOSFETs and
D1 are selected based on voltage, load and efficiency re-
quirements. C
RMS currents in the converter and C
enough ESR to meet the output voltage ripple and transient
specifications. Finally, the loop compensation components
are chosen to meet the desired transient specifications.
Operating Frequency
The choice of operating frequency and inductor value is a
trade off between efficiency and component size. Low
frequency operation improves efficiency by reducing
MOSFET switching losses and gate charge losses. How-
ever, lower frequency operation requires more induc-
tance for a given amount of ripple current, resulting in a
larger inductor size and higher cost. If the ripple current
is allowed to increase, larger output capacitors may be
required to maintain the same output ripple. For convert-
ers with high step-down V
consideration is the minimum on-time of the LTC3703-5
(see the Minimum On-time Considerations section). A
final consideration for operating frequency is that in
12
IN
is selected for its ability to handle the large
U
U
(Refer to Functional Diagram)
SET
U
IN
and L can be chosen. The
to V
W
OUT
OUT
is chosen with low
ratios, another
U
of the operating mode with the following exceptions: In
boost mode, Pulse Skip Mode operation is always dis-
abled regardless of the level of the MODE/SYNC pin and
the line feedforward compensation is also disabled. The
overcurrent circuitry continues to monitor the load current
by looking at the drain voltage of the main (bottom side)
MOSFET. In boost mode, however, the peak MOSFET
current does not equal the load current but instead
I
account when programming the I
noise-sensitive communications systems, it is often de-
sirable to keep the switching noise out of a sensitive
frequency band.
The LTC3703-5 uses a constant frequency architecture
that can be programmed over a 100kHz to 600kHz range
with a single resistor from the f
in the circuit on the first page of this data sheet. The
nominal voltage on the f
flows from this pin is used to charge and discharge an
internal oscillator capacitor. The value of R
operating frequency can be chosen from Figure 6 or from
the following equation:
D
= I
R
SET
LOAD
(
k
Ω =
/(1 – D). This factor needs to be taken into
1000
100
Figure 6. Timing Resistor (R
)
10
1
0
f kHz
(
7100
200
) –
SET
FREQUENCY (kHz)
25
400
pin is 1.2V, and the current that
SET
600
pin to ground, as shown
MAX
SET
800
voltage.
) Value
37035 F06
SET
1000
for a given
37035fa