LTC1709EG-8 Linear Technology, LTC1709EG-8 Datasheet - Page 16

• Manufacturer Part Number: LTC1709EG-8
• Description: IC REG SW 2PH SYNC STPDWN 36SSOP
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LTC1709EG-8

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 2
• Voltage - Output: 1.3 ~ 3.5 V
• Current - Output: 3A
• Voltage - Input: 4 ~ 36 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 36-SSOP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -
• Frequency - Switching: -

APPLICATIO S I FOR ATIO
LTC1709-8/LTC1709-9
EXTV
The LTC1709 contains an internal P-channel MOSFET
switch connected between the EXTV
When the voltage applied to EXTV
internal regulator is turned off and an internal switch
closes, connecting the EXTV
thereby supplying internal and MOSFET gate driving power
to the IC. The switch remains closed as long as the voltage
applied to EXTV
MOSFET driver and control power to be derived from the
output during normal operation (4.7V < V
from the internal regulator when the output is out of
regulation (start-up, short-circuit). Do not apply greater
than 7V to the EXTV
0.3V when using the application circuits shown. If an
external voltage source is applied to the EXTV
the V
series with the LTC1709’s V
between the EXTV
from backfeeding V
Significant efficiency gains can be realized by powering
INTV
from the driver and control currents will be scaled by the
ratio: (Duty Factor)/(Efficiency). For 5V regulators this
means connecting the EXTV
ever, for 3.3V and other lower voltage regulators, addi-
tional circuitry is required to derive INTV
output.
16
Figure 5a. Secondary Output Loop with EXTV
CC
CC
IN
OPTIONAL EXTV
CONNECTION
5V < V
EXTV
supply is not present, a diode can be placed in
from the output, since the V
Connection
CC
SEC
LTC1709
< 7V
CC
CC
PGND
CC
SW1
TG1
BG1
U
remains above 4.5V. This allows the
V
CC
IN
IN
and the V
.
pin and ensure that EXTV
C
IN
N-CH
N-CH
U
+
CC
IN
CC
pin directly to V
pin and a Schottky diode
IN
CC
pin to the INTV
V
1N4148
pin, to prevent current
IN
W
T1
rises above 4.7V, the
CC
IN
CC
and INTV
current resulting
EXTVCC
power from the
CC
R
SENSE
Connection
V
CC
SEC
OUT
+
+
U
< 7V) and
CC
pin when
CC
1709 F05a
< V
. How-
CC
1 F
C
V
OUT
pins.
OUT
IN
pin
+
The following list summarizes the four possible connec-
tions for EXTV
1. EXTV
to be powered from the internal 5V regulator resulting in
a significant efficiency penalty at high input voltages.
2. EXTV
connection for a 5V regulator and provides the highest
efficiency.
3. EXTV
supply is available in the 5V to 7V range, it may be used to
power EXTV
gate drive requirements.
4. EXTV
For 3.3V and other low voltage regulators, efficiency gains
can still be realized by connecting EXTV
derived voltage which has been boosted to greater than
4.7V but less than 7V. This can be done with either the
inductive boost winding as shown in Figure 5a or the
capacitive charge pump shown in Figure 5b. The charge
pump has the advantage of simple magnetics.
Topside MOSFET Driver Supply (C
Functional Diagram)
External bootstrap capacitors C
the BOOST1 and BOOST2 pins supply the gate drive
voltages for the topside MOSFETs. Capacitor C
Functional Diagram is charged though diode D
EXTV
CC
CC
CC
CC
Figure 5b. Capacitive Charge Pump for EXTV
CC
left open (or grounded). This will cause INTV
connected to an output-derived boost network.
LTC1709
connected to an external supply. If an external
connected directly to V
CC
CC:
providing it is compatible with the MOSFET
PGND
SW1
TG1
BG1
V
IN
C
IN
N-CH
N-CH
+
B1
BAT85
V
OUT
IN
and C
L1
B
,D
. This is the normal
VN2222LL
B
0.22 F
) (Refer to
CC
B2
R
SENSE
to an output-
connected to
+
+
CC
B
1709 F05b
BAT85
B
BAT85
C
V
in the
OUT
OUT
from
CC