LTC1539 LINER [Linear Technology], LTC1539 Datasheet - Page 16

• Manufacturer Part Number: LTC1539
• Description: Dual High Efficiency, Low Noise, Synchronous Step-Down Switching Regulators
• Manufacturer: LINER [Linear Technology]

4. EXTV
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
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
2) pin follows. With the topside MOSFET on, the boost
voltage is above the input supply: V
The value of the boost capacitor C
that of the total input capacitance of the topside MOSFET(s).
The reverse breakdown on D
V
LTC1538-AUX/LTC1539
APPLICATIONS
16
IN(MAX)
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
it may be used to power EXTV
ible with the MOSFET gate drive requirements. When
driving standard threshold MOSFETs, the external sup-
ply must be always present during operation to prevent
MOSFET failure due to insufficient gate drive. Note: care
must be taken when using the connections in items 3 or
4. These connections will effect the INTV
when either or both controllers are on.
Figure 4a. Secondary Output Loop and EXTV
R6
R5
OPTIONAL EXTV
CONNECTION
5V V
EXTV
SFB1
SGND
LTC1538-AUX
CC
.
LTC1539*
connected to an external supply. If an external
CC
SEC
TGS1*
PGND
TGL1
SW1
BG1
9V
V
IN
CC
+
U
*TGS1 ONLY AVAILABLE ON THE LTC1539
C
N-CH
IN
INFORMATION
U
N-CH
N-CH
IN
V
B
B
IN
B
B
and the BOOST 1(BOOST
in the Functional Diagram
CC
from INTV
connected to the BOOST
•
B
must be greater than
providing it is compat-
BOOST
needs to be 100 times
W
B
1:1
L1
,D
1N4148
B
•
)
B
= V
CC
voltage across
R
CC
Connection
IN
SENSE
V
CC
SEC
+ V
U
when the
1538 F04a
+
+
CC
voltage
INTVCC
1 F
C
V
V
OUT
OUT
IN
)
.
Output Voltage Programming
The LTC1538-AUX/LTC1539 have pin selectable output
voltage programming. The output voltage is selected by
the V
The top of an internal resistive divider is connected to
SENSE
applications the SENSE
voltage as shown in Figure 5a. When using an external
resistive divider for Controller 2, the V
Figure 5a. LTC1538-AUX/LTC1539 Fixed Output Applications
*TGS1 ONLY AVAILABLE ON THE LTC1539
V
V
V
Figure 5b. LTC1538-AUX/LTC1539 Adjustable Applications
PROG1,2
PROG1,2
PROG2
LTC1538-AUX
EXTV
PROG1
LTC1539*
–
CC
Figure 4b. Capacitive Charge Pump for EXTV
1 pin in Controller 1. For fixed output voltage
TGS1*
PGND
TGL1
SW1
= Open (DC)
BG1
V
(V
IN
= 0V
= INTV
LTC1538-AUX
PROG2
*LTC1539 ONLY
LTC1538-AUX
+
LTC1539
LTC1539
SENSE
V
V
V
OSENSE2
PROG1
SGND
PROG2
CC
C
N-CH
SGND
) pin as follows:
IN
–
1
*
–
N-CH
N-CH
1 pin is connected to the output
V
GND: V
INTV
IN
OPEN (DC)
V
OUT
CC
BAT85
OUT
: V
= 1.19V 1 +
L1
V
V
V
OUT
100pF
1.19V V
= 3.3V
OUT1,2
OUT1,2
OUT2
= 5V
+
PROG2
VN2222LL
= Adjustable
R
OUT
R2
R1
0.22 F
C
SENSE
= 3.3V
= 5V
OUT
R2
R1
1538 F05a
V
pin is left open
1538 F05b
OUT
9V
+
+
CC
1 F
BAT85
C
BAT85
1538 F04b
OUT
V
OUT