LTC1772BES6 View Datasheet(PDF) - Linear Technology

Part Name

Description

MFG CO.

LTC1772BES6

Constant Frequency Current Mode Step-Down DC/DC Controller in SOT-23

Linear Technology 

1 2 3 4 5 6 7 8 9 10 Next

LTC1772B

W

FUNCTIONAL DIAGRA

VIN SENSE–

5

4

15mV

+

ICMP

–

SLOPE

OSC

COMP

FREQ

FOLDBACK

0.3V

SHORT-CIRCUIT

DETECT

RS1

R

Q

SWITCHING

LOGIC AND

BLANKING

S

CIRCUIT

OVP

EAMP

0.5µA

1 ITH/RUN

VIN

0.35V +

VOLTAGE

VREF

REFERENCE

0.8V

SHDN

CMP

SHDN

GND

–

UV

2

UNDERVOLTAGE

LOCKOUT

VIN

PGATE

6

VREF

+

60mV

VREF

0.8V

VFB

3

VIN

1.2V

1772FD

U

OPERATIO (Refer to Functional Diagram)

Main Control Loop

The LTC1772B is a constant frequency current mode

switching regulator. During normal operation, the external

P-channel power MOSFET is turned on each cycle when

the oscillator sets the RS latch (RS1) and turned off when

the current comparator (ICMP) resets the latch. The peak

inductor current at which ICMP resets the RS latch is

controlled by the voltage on the ITH/RUN pin, which is the

output of the error amplifier EAMP. An external resistive

divider connected between VOUT and ground allows the

EAMP to receive an output feedback voltage VFB. When the

load current increases, it causes a slight decrease in VFB

relative to the 0.8V reference, which in turn causes the

ITH/RUN voltage to increase until the average inductor

current matches the new load current.

The main control loop is shut down by pulling the ITH/RUN

pin low. Releasing ITH/RUN allows an internal 0.5µA

current source to charge up the external compensation

network. When the ITH/RUN pin reaches 0.35V, the main

control loop is enabled with the ITH/RUN voltage then

pulled up to its zero current level of approximately 0.85V.

As the external compensation network continues to charge

4

Share Link: