LT1308B Linear Technology, LT1308B Datasheet - Page 5

• Manufacturer Part Number: LT1308B
• Description: High Current/ Micropower Single Cell/ 600kHz DC/DC Converters
• Manufacturer: Linear Technology

BLOCK
SW (Pin 5): Switch Pin. Connect inductor/diode here.
Minimize trace area at this pin to keep EMI down.
V
right at the pin, connected directly to ground.
LBI (Pin 7): Low-Battery Detector Input. 200mV refer-
ence. Voltage on LBI must stay between ground and
APPLICATIONS
LAYOUT HINTS
The LT1308 switches current at high speed, mandating
careful attention to layout for proper performance. You will
not get advertised performance with careless layouts.
Figure 2 shows recommended component placement.
Follow this closely in your PC layout. Note the direct path
of the switching loops. Input capacitor C
close (< 5mm) to the IC package. As little as 10mm of wire
or PC trace from C
inability to regulate or oscillation. A 10 F ceramic bypass
capacitor is the only input capacitance required provided
the battery has a low inductance path to the circuit . The
battery itself provides the bulk capacitance the device
requires for proper operation. If the battery is located some
PIN
IN
U
(Pin 6): Supply Pin. Must have local bypass capacitor
V
OUT
FUNCTIONS
R1
(EXTERNAL)
R2
(EXTERNAL)
FB
U
DIAGRAM
IN
U
V
FB
6
2
IN
U
to V
INFORMATION
IN
W
U
Q1
R5
40k
will cause problems such as
Q2
W
R6
40k
R3
30k
R4
140k
10
IN
V
IN
+
–
OSCILLATOR
GENERATOR
must be placed
600kHz
RAMP
g
AMPLIFIER
m
ERROR
U
+
+
BIAS
V
1
C
700mV. Low-battery detector does not function with
SHDN pin grounded. If not used, float LBI pin.
LBO (Pin 8): Low-Battery Detector Output. Open collec-
tor, can sink 10 A. A 1M pullup is recommended. LBO
is high impedance when SHDN is grounded.
Figure 2. Recommended Component Placement. Traces
Carrying High Current Are Direct. Trace Area at FB Pin and V
Pin is Kept Low. Lead Length to Battery Should Be Kept Short.
Ground Plane Should Be Placed Under All Components
+
–
–
+
COMPARATOR
A1
A2
MULTIPLE
VIAs
ENABLE
R
200mV
FF
S
1
2
3
4
GND
GROUND PLANE
LBI
7
Q
C
LT1308
IN
–
+
SHUTDOWN
C
OUT
DRIVER
A = 3
A4
8
7
6
5
+
–
V
L
OUT
SHDN
GND
LBO
SW
D
3
8
5
4
Q3
0.03
LT1308
1308 BD
1308 F02
V
IN
5
C