LTC1872ES6 LINER [Linear Technology], LTC1872ES6 Datasheet - Page 4

• Manufacturer Part Number: LTC1872ES6
• Description: Constant Frequency Current Mode Step-Up DC/DC Controller in SOT-23
• Manufacturer: LINER [Linear Technology]

FUNCTIONAL DIAGRA
OPERATIO
LTC1872
Main Control Loop
The LTC1872 is a constant frequency current mode switch-
ing regulator. During normal operation, the external
N-channel power MOSFET is turned on each cycle by the
oscillator and turned off when the current comparator
(ICMP) resets the RS latch. The peak inductor current at
which ICMP resets the RS latch is controlled by the voltage
on the I
amplifier EAMP. An external resistive divider connected
between V
output feedback voltage V
creases, it causes a slight decrease in V
4
U
0.3V
TH
V
OUT
/RUN pin, which is the output of the error
IN
GND
V
5
2
U
IN
and ground allows the EAMP to receive an
SENSE
U
4
4
–
(Refer to Functional Diagram)
FOLDBACK
FB
FREQ
OSC
. When the load current in-
+
–
–
+
W
ICMP
FB
0.5 A
UNDERVOLTAGE
SLOPE
COMP
relative to the
REFERENCE
VOLTAGE
LOCKOUT
V
+
–
IN
0.15V
0.3V
V
0.8V
REF
0.8V reference, which in turn causes the
I
current matches the new load current.
The main control loop is shut down by pulling the I
pin low. Releasing I
current source to charge up the external compensation
network. When the I
control loop is enabled with the I
pulled up to its zero current level of approximately 0.7V.
As the external compensation network continues to charge
up, the corresponding output current trip level follows,
allowing normal operation.
TH
0.35V
/RUN voltage to increase until the average inductor
+
–
1
I
R
S
TH
RS
/RUN
+
–
Q
SHDN
BURST
CMP
CMP
SLEEP
SWITCHING
LOGIC AND
BLANKING
CIRCUIT
SHDN
UV
TH
TH
/RUN pin reaches 0.35V, the main
/RUN allows an internal 0.5 A
EAMP
OVP
TH
+
–
+
–
/RUN voltage then
1.2V
V
IN
V
+
60mV
V
0.8V
REF
REF
V
IN
1872FD
NGATE
V
TH
6
3
FB
/RUN