LTC1709EG-7 Linear Technology, LTC1709EG-7 Datasheet - Page 17

• Manufacturer Part Number: LTC1709EG-7
• Description: IC SW REG STEP-DOWN SYNC 36-SSOP
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LTC1709EG-7

• 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
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
INTV
turns on, the driver places the C
source of the desired MOSFET. This enhances the MOSFET
and turns on the topside switch. The switch node voltage,
SW, rises to V
The value of the boost capacitor C
times that of the total input capacitance of the topside
MOSFET(s). The reverse breakdown of D
than V
The final arbiter when defining the best gate drive ampli-
tude level will be the input supply current. If a change is
made that decreases input current, the efficiency has
improved. If the input current does not change then the
efficiency has not changed either.
Output Voltage
The LTC1709-7 has a true remote voltage sense capablity.
The sensing connections should be returned from the load
back to the differential amplifier’s inputs through a com-
mon, tightly coupled pair of PC traces. The differential
amplifier corrects for DC drops in both the power and
ground paths. The differential amplifier output signal is
R6
R5
Figure 5a. Secondary Output Loop with EXTV
CC
IN(MAX).
OPTIONAL EXTV
CONNECTION
5V < V
EXTV
FCB
when the SW pin is low. When the topside MOSFET
CC
SEC
LTC1709-7
IN
< 7V
and the BOOST pin rises to V
CC
U
PGND
SW1
BG1
TG1
V
IN
C
IN
U
N-CH
N-CH
+
B
B1
voltage across the gate-
B
and C
V
1N4148
needs to be 30 to 100
W
B
IN
,D
T1
B
B
) (Refer to
B2
must be greater
CC
connected to
R
Connection
IN
SENSE
V
SEC
+ V
U
+
+
B
B
INTVCC
17097 F05a
in the
from
1 F
C
V
OUT
OUT
.
divided down and compared with the internal precision
0.8V voltage reference by the error amplifier.
Output Voltage Programming
The output voltage is digitally programmed as defined in
Table 1 using the VID0 to VID4 logic input pins. The VID
logic inputs program a precision, 0.25% internal feedback
resistive divider. The LTC1709-7 has an output voltage
range of 0.9V to 2V in 25mV and 50mV steps.
Between the ATTENOUT pin and ground is a variable
resistor, R1, whose value is controlled by the five VID input
pins (VID0 to VID4). Another resistor, R2, between the
ATTENIN and the ATTENOUT pins completes the resistive
divider. The output voltage is thus set by the ratio of
(R1 + R2) to R1.
Each VID digital input is pulled up by a 40k resistor in
series with a diode from V
grounded to get a digital low input, and can be either
floated or connected to V
series diode is used to prevent the digital inputs from
being damaged or clamped if they are driven higher than
V
V
normally connected to INTV
other sources. If it is driven from another source, that
source must be in the range of 2.7V to 5.5V and must be
alive prior to enabling the LTC1709-7.
BIAS
BIAS
EXTV
. The digital inputs accept CMOS voltage levels.
is the supply voltage for the VID section. It is
Figure 5b. Capacitive Charge Pump for EXTV
CC
LTC1709-7
PGND
SW1
TG1
BG1
V
IN
C
IN
BIAS
N-CH
N-CH
+
to get a digital high input. The
BIAS
CC
BAT85
but can be driven from
. Therefore, it must be
V
IN
L1
LTC1709-7
VN2222LL
0.22 F
R
SENSE
+
+
CC
17097 F05b
BAT85
17
BAT85
C
V
OUT
OUT