LTC3703EG-5#TR Linear Technology, LTC3703EG-5#TR Datasheet - Page 16

• Manufacturer Part Number: LTC3703EG-5#TR
• Description: IC BUCK/BOOST SYNC ADJ 5A 28SSOP
• Manufacturer: Linear Technology
• Type: Step-Down (Buck), Step-Up (Boost)r

Specifications of LTC3703EG-5#TR

• 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 ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 28-SSOP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -

LTC3703-5
APPLICATIO S I FOR ATIO
value. Typically, once the ESR requirement is satisfied the
capacitance is adequate for filtering and has the required
RMS current rating.
Manufacturers such as Nichicon, Nippon Chemi-Con and
Sanyo should be considered for high performance
throughhole capacitors. The OS-CON (organic semicon-
ductor dielectric) capacitor available from Sanyo has the
lowest product of ESR and size of any aluminum electro-
lytic at a somewhat higher price. An additional ceramic
capacitor in parallel with OS-CON capacitors is recom-
mended to reduce the effect of their lead inductance.
In surface mount applications, multiple capacitors placed
in parallel may be required to meet the ESR, RMS current
handling and load step requirements. Dry tantalum, spe-
cial polymer and aluminum electrolytic capacitors are
available in surface mount packages. Special polymer
capacitors offer very low ESR but have lower capacitance
density than other types. Tantalum capacitors have the
highest capacitance density but it is important to only use
types that have been surge tested for use in switching
power supplies. Several excellent surge-tested choices
are the AVX TPS and TPSV or the KEMET T510 series.
Aluminum electrolytic capacitors have significantly higher
ESR, but can be used in cost-driven applications providing
that consideration is given to ripple current ratings and
long term reliability. Other capacitor types include
Panasonic SP and Sanyo POSCAPs.
Output Voltage
The LTC3703-5 output voltage is set by a resistor divider
according to the following formula:
The external resistor divider is connected to the output as
shown in the Functional Diagram, allowing remote voltage
sensing. The resultant feedback signal is compared with
the internal precision 800mV voltage reference by the
error amplifier. The internal reference has a guaranteed
tolerance of ±1%. Tolerance of the feedback resistors will
add additional error to the output voltage. 0.1% to 1%
resistors are recommended.
16
V
OUT
=
0 8 1
.
V
⎛
⎜
⎝
+
U
R
R
2
1
⎞
⎟
⎠
U
W
U
MOSFET Driver Supplies (DRV
The LTC3703-5 drivers are supplied from the DRV
BOOST pins (see Figure 2), which have an absolute
maximum voltage of 15V. If the main supply voltage, V
is higher than 15V a separate supply with a voltage
between 5V and 15V must be used to power the drivers. If
a separate supply is not available, one can easily be
generated from the main supply using one of the circuits
shown in Figure 9. If the output voltage is between 5V and
15V, the output can be used to directly power the drivers
as shown in Figure 9a. If the output is below 5V, Figure 9b
shows an easy way to boost the supply voltage to a
sufficient level. This boost circuit uses the LT1613 in a
ThinSOT
area (<0.2 in
winding on the inductor (Figure 9c) or a capacitive charge
pump (Figure 9d). All the circuits shown in Figure 9
require a start-up circuit (Q1, D1 and R1) to provide driver
power at initial start-up or following a short-circuit. The
resistor R1 must be sized so that it supplies sufficient base
current and zener bias current at the lowest expected value
of V
capable of supplying the required gate driver current
which can be estimated from:
This equation for I
the circuit components shown in Figure 9.
An external bootstrap capacitor, C
BOOST pin supplies the gate drive voltage for the topside
MOSFETs. Capacitor C
diode, D
the top side MOSFET is turned on, the driver places the C
voltage across the gate-source of the top MOSFET. The
switch node voltage, SW, rises to V
follows. With the topside MOSFET on, the boost voltage
is above the input supply: V
value of the boost capacitor C
of the total input capacitance of the top side MOSFET(s).
The reverse breakdown of the external diode, D
greater than V
for the external diode is the reverse recovery and reverse
leakage, either of which may cause excessive reverse
ThinSOT is a tradmark of Linear Technology Corporation.
I
DRVCC
IN
. When using an existing supply, the supply must be
B
TM
, from the DRV
= (f)(Q
package and a chip inductor for minimal extra
2
). Two other possible schemes are an extra
IN(MAX)
G(TOP)
DRVCC
. Another important consideration
+ Q
CC
B
is also useful for properly sizing
is charged through external
G(BOTTOM)
supply when SW is low. When
BOOST
B
needs to be 100 times that
CC
and BOOST)
IN
= V
B
)
, connected to the
and the BOOST pin
IN
+ V
DRVCC
B
, must be
CC
. The
37035fa
and
IN
B
,