LTC1622
Low Input Voltage
Current Mode Step-Down
DC/DC Controller
FEATURES
s
s
s
s
s
s
s
s
s
DESCRIPTIO
s
s
s
s
High Efficiency
Constant Frequency 550kHz Operation
V
IN
Range: 2V to 10V
Multiampere Output Currents
OPTI-LOOP
TM
Compensation Minimizes C
OUT
Selectable, Burst Mode Operation
Low Dropout Operation: 100% Duty Cycle
Synchronizable up to 750kHz
Current Mode Operation for Excellent Line and Load
Transient Response
Low Quiescent Current: 350µA
Shutdown Mode Draws Only 15µA Supply Current
±1.9%
Reference Accuracy
Available in 8-Lead MSOP
APPLICATIO S
s
s
s
s
s
s
s
1- or 2-Cell Li-Ion Powered Applications
Cellular Telephones
Wireless Modems
Portable Computers
Distributed 3.3V, 2.5V or 1.8V Power Systems
Scanners
Battery-Powered Equipment
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode and OPTI-LOOP are a trademarks of Linear Technology Corporation.
The LTC
®
1622 is a constant frequency current mode step-
down DC/DC controller providing excellent AC and DC load
and line regulation. The device incorporates an accurate
undervoltage feature that shuts the LTC1622 down when
the input voltage falls below 2V.
The LTC1622 boasts a
±1.9%
output voltage accuracy and
consumes only 350µA of quiescent current. For applica-
tions where efficiency is a prime consideration and the
load current varies from light to heavy, the LTC1622 can
be configured for Burst Mode
TM
operation. Burst Mode
operation enhances low current efficiency and extends
battery run time. Burst Mode operation is inhibited during
synchronization or when the SYNC/MODE pin is pulled low
to reduce noise and possible RF interference.
High constant operating frequency of 550kHz allows the
use of a small inductor. The device can also be synchro-
nized up to 750kHz for special applications. The high
frequency operation and the available 8-lead MSOP pack-
age create a high performance solution in an extremely
small amount of PCB area.
To further maximize the life of the battery source, the
P-channel MOSFET is turned on continuously in dropout
(100% duty cycle). In shutdown, the device draws a mere
15µA.
TYPICAL APPLICATIO
8
2
R1
10k
C3
220pF
4
470pF
V
IN
I
TH
SENSE
–
1
V
IN
2.5V TO 8.5V
R2
0.03Ω
Si3443DV L1
4.7µH
D1
IR10BQ015
R3
159k
R4
75k
L1: MURATA LQN6C-4R7
R2: DALE WSL-1206 0-03Ω
C1
10µF
10V
Efficiency vs Load Current with
Burst Mode Operation Enabled
100
V
IN
= 4.2V
90
EFFICIENCY (%)
V
IN
= 3.3V
7
PDRV
LTC1622
5
SYNC/MODE
6
80
V
IN
= 6V
70
60
50
V
OUT
= 2.5V
R
SENSE
= 0.03Ω
1
100
1000
10
LOAD CURRENT (mA)
5000
1622 F01b
V
OUT
2.5V
1.5A
RUN/SS
GND
V
FB
3
+
C2
47µF
6V
C1: TAIYO YUDEN CERAMIC EMK325BJ106MNT
C2: SANYO POSCAP 6TPA47M
D1: INTERNATIONAL RECTIFIER IR10BQ015
1622 F01a
40
Figure 1. High Efficiency Step-Down Converter
U
V
IN
= 8.4V
U
U
1