LTC1439 Linear Technology, LTC1439 Datasheet - Page 16

• Manufacturer Part Number: LTC1439
• Description: Dual High Efficiency/ Low Noise/ Synchronous Step-Down Switching Regulators
• Manufacturer: Linear Technology

2. EXTV
3. EXTV
4. EXTV
LTC1438/LTC1439
APPLICATIONS
16
in an efficiency penalty of up to 10% at high input
voltages.
connection for a 5V regulator and provides the highest
efficiency.
For 3.3V and other low voltage regulators, efficiency
gains can still be realized by connecting EXTV
output-derived voltage which has been boosted to
greater than 4.8V. This can be done with either the
inductive boost winding as shown in Figure 4a or the
capacitive charge pump shown in Figure 4b. The charge
pump has the advantage of simple magnetics.
supply is available in the 5V to 10V range (EXTV
V
Figure 4a. Secondary Output Loop and EXTV
*TGS1 ONLY AVAILABLE ON THE LTC1439
IN
EXTV
) it may be used to power EXTV
R6
R5
LTC1438
LTC1439*
CC
CC
CC
Figure 4b. Capacitive Charge Pump for EXTV
OPTIONAL EXTV
CONNECTION
5V V
CC
EXTV
SFB1
SGND
TGS1*
connected to an output-derived boost network.
LTC1438
LTC1439*
connected directly to V
connected to an external supply. If an external
PGND
TGL1
SW1
BG1
CC
V
SEC
IN
TGS1*
PGND
TGL1
SW1
BG1
+
9V
V
IN
CC
U
+
C
N-CH
IN
*TGS1 ONLY AVAILABLE ON THE LTC1439
C
N-CH
INFORMATION
N-CH
IN
N-CH
U
V
IN
N-CH
N-CH
V
BAT85
IN
L1
OUT
•
W
1:1
L1
. This is the normal
VN2222LL
CC
1N4148
R
0.22 F
•
SENSE
CC
providing it is
Connection
R
SENSE
+
+
V
U
CC
SEC
CC
1438 F04a
+
+
1 F
BAT85
BAT85
C
1438 F04b
OUT
V
to an
OUT
CC
1 F
C
V
OUT
OUT
Topside MOSFET Driver Supply (C
External bootstrap capacitors C
1 and BOOST 2 pins supply the gate drive voltages for the
topside MOSFETs. Capacitor C
gram is charged through diode D
SW1(SW2) pin is low. When one of the topside MOSFETs
is to be turned on, the driver places the C
the gate source of the desired MOSFET. This enhances
the MOSFET and turns on the topside switch. The switch
node voltage SW1(SW2) rises to V
1(BOOST 2) pin follows. With the topside MOSFET on,
the boost voltage is above the input supply: V
+ V
be 100 times that of the total input capacitance of the
topside MOSFET(s). The reverse breakdown on D
be greater than V
Output Voltage Programming
The LTC1438/LTC1439 have pin selectable output voltage
programming. Controller 1 on the LTC1438-ADJ is a
dedicated adjustable controller. The output voltage is
selected by the V
other parts:
Except for the LTC1438-ADJ, the top of an internal resis-
tive divider is connected to SENSE
For fixed output voltage applications the SENSE
connected to the output voltage as shown in Figure 5a.
When using an external resistive divider for an adjustable
regulator, the V
left open on the LTC1438-ADJ) and the V
connected to the feedback resistors as shown in Figure 5b.
The adjustable controller will force the externally attenu-
ated output voltage to 1.19V.
compatible with the MOSFET gate drive requirements.
When driving standard threshold MOSFETs, the exter-
nal supply must be always present during operation to
prevent MOSFET failure due to insufficient gate drive.
V
V
V
INTVCC
PROG1,2
PROG1,2
PROG2
. The value of the boost capacitor C
= Open (DC)
= 0V
= INTV
PROG2
PROG1
IN(MAX)
CC
pin is left open (V
(V
PROG2
.
) pin as follows on all of the
B
B
V
V
V
connected to the BOOST
B
OUT1,2
OUT1,2
OUT2
in the Functional Dia-
from INTV
–
B
1 pin in Controller 1.
, D
IN
PROG1
= Adjustable
B
and the BOOST
B
= 3.3V
= 5V
)
voltage across
OSENSE2
CC
is internally
BOOST
B
when the
needs to
–
1 pin is
B
pin is
must
= V
IN