Datasheet

5
LT1614
NFB (Pin 1): Negative Feedback Pin. Reference voltage is
–1.24V. Connect resistive divider tap here. The sug-
gested value for R2 is 24.9k. Set R1 and R2 according to:
R
V
R
OUT
1
124
124
2
45 10
6
=
+




||–.
.
.•
–
V
C
(Pin 2): Compensation Pin for Error Amplifier. Con-
nect a series RC from this pin to ground. Typical values
are 100kΩ and 1nF. Minimize trace area at V
C
.
SHDN (Pin 3): Shutdown. Ground this pin to turn off
switcher. Must be tied to V
IN
(or higher voltage) to enable
switcher. Do not float the SHDN pin.
PIN FUNCTIONS
UUU
GND (Pin 4): Ground. Connect directly to local ground
plane.
SW (Pin 5): Switch Pin. Minimize trace area at this pin to
keep EMI down.
V
IN
(Pin 6): Supply Pin. Must have 1µF ceramic bypass
capacitor 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
700mV. Float this pin if not used.
LBO (Pin 8): Low-Battery Detector Output. Open collec-
tor, can sink 10µA. A 1MΩ pull-up is recommended. Float
this pin if not used. The low-battery detector is disabled
when SHDN is low. LBO is high-Z in this state.
BLOCK DIAGRAM
W
–
+
–
+
–
+
–
+
–
+
+
+
Σ
COMPARATOR
RAMP
GENERATOR
R
BIAS
V
C
g
m
Q2
×10
Q1
NFB
NFB
ENABLE
200mV
A = 3
FF
A2
ERROR
AMPLIFIER
A1
A4
0.15Ω
DRIVER
SW
GND
1614 BD
Q3
Q
S
600kHz
OSCILLATOR
5
LBO
LBI
SHDN
SHUTDOWN
3
7
2
4
R6
40k
R5
40k
R1
(EXTERNAL)
R3
30k
R4
140k
1
V
IN
V
IN
V
OUT
6
8
R2
(EXTERNAL)
Figure 2. Block Diagram