LTC3700EMS View Datasheet(PDF) - Linear Technology
Part Name
Description
Manufacturer
LTC3700EMS Datasheet PDF : 16 Pages
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LTC3700
Constant Frequency
Step-Down DC/DC Controller
with LDO Regulator
FEATURES
DESCRIPTIO
s Dual Output Regulator in Tiny 10-Pin MSOP
s High Efficiency: Up to 94%
s Wide VIN Range: 2.65V to 9.8V
s Constant Frequency 550kHz Operation
s 150mA LDO Regulator with Current Limit and
Thermal Shutdown Protection
s High Output Currents Easily Achieved
s Burst Mode® Operation at Light Load
s Low Dropout: 100% Duty Cycle
s Current Mode Operation for Excellent Line and Load
Transient Response
s 0.8V Reference Allows Low Output Voltages
s Low Quiescent Current: 260µA Total
s Shutdown Mode Draws Only 10µA Supply Current
s Common Power Good Output for Both Supplies
U
APPLICATIO S
s Notebook Computers
s Portable Instruments
s One or Two Li-Ion Battery-Powered Applications
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a registered trademark of Linear Technology Corporation.
The LTC®3700 is a constant frequency current mode step-
down (buck) DC/DC controller with excellent AC and DC
load and line regulation. The on-chip 150mA low dropout
(LDO) linear regulator can be powered from the buck
controller’s input supply, its own independent input supply
or the buck regulator’s output. The buck controller incor-
porates an undervoltage lockout feature that shuts down the
controller when the input voltage falls below 2.1V.
The buck regulator provides a ±2.5% output voltage accu-
racy. It consumes only 210µA of quiescent current in nor-
mal operation with the LDO consuming an additional 50µA.
In shutdown, a mere 10µA (combined) is consumed.
For applications where efficiency is a prime consideration,
the buck controller is configured for Burst Mode operation
which enhances efficiency at low output current. To fur-
ther maximize the life of a battery source, the external
P-channel MOSFET is turned on continuously in dropout
(100% duty cycle). High constant operating frequency of
550kHz allows the use of a small external inductor.
The LDO is protected by both current limit and thermal
shutdown circuits.
The LTC3700 is available in a tiny 10-pin MSOP.
TYPICAL APPLICATIO
VIN1
5V
VOUT1
1.8V
AT 1A
C2 +
47µF
6V
C1
10µF
10V
R1
0.068Ω
VIN
SENSE–
VIN2
LDO
L1 M1
10µH
PGATE
VFB2
100k
D1
LTC3700
80.6k
10k
220pF
VFB PGOOD
ITH/RUN GND
VIN2
C3
3.3V
10µF
10V
VOUT2
2.5V AT
169k
C4 150mA
2.2µF
78.7k
16V
C1, C3: TAIYO YUDEN EMK325BJ106MNT
C2: SANYO POSCAP 6TPA47M
C4: MURATA GRM42-6X7R225K016AL
D1: MOTOROLA MBRM120T3
L1: COILTRONICS UP1B-100
M1: Si3443DV
R1: DALE 0.25W
3700 F01
Figure 1. High Efficiency 5V to 1.8V/1A Buck with 3.3V to 2.5V/150mA LDO
Buck Efficiency vs Load Current
90
VOUT = 1.8V
86 RSENSE = 0.068Ω
82
VIN = 3.3V
78
74
VIN = 5V
70
VIN = 4.2V
66
62
58
54
50
1
10
100
LOAD CURRENT (mA)
1000
3700 F01a
3700f
1
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