LTC1771
10m A Quiescent Current
High Efficiency Step-Down
DC/DC Controller
FEATURES
DESCRIPTIO
n
Very Low Standby Current: 10m A The LTC 1771 is a high efficiency current mode step-
n
Available in Space-Saving 8-Lead MSOP Package down DC/DC controller that draws as little as 10m A DC
n
Output Currents: Up to 5A supply current to regulate the output at no load while
n
Wide V Range: 2.8V to 20V Operation maintaining high efficiency for loads up to several amps.
IN
n
V Range: 1.23V to 18V
OUT
The LTC1771 drives an external P-channel power MOSFET
n
High Efficiency: Over 93% Possible
using a current mode, constant off-time architecture. An
n
2% Output Accuracy
external sense resistor is used to program the operating
n
Very Low Dropout Operation: 100% Duty Cycle
current level. Current mode control provides short-circuit
n
Current Mode Operation for Excellent Line and
protection, excellent transient response and controlled
Load Transient Response
start-up behavior. Burst Mode operation enables the
TM
n
Defeatable Burst Mode Operation
LTC1771 to maintain high efficiency down to extremely
n
Short-Circuit Protected
low currents. Shutdown mode further reduces the supply
n
Optional Programmable Soft-Start
current to a mere 2m A. For low noise applications, Burst
n
Micropower Shutdown: I = 2m A
Q
Mode operation can be easily disabled with the MODE pin.
U
Wide input supply range of 2.8V to 18V (20V maximum)
APPLICATIO S
and 100% duty cycle operation for low dropout make the
n
LTC1771 ideal for a wide variety of battery-powered appli-
Cellular Telephones and Wireless Modems
n
cations where maximizing battery life is important.
1- to 4-Cell Lithium-Ion-Powered Applications
n
Portable Instruments
The LTC1771s availability in both 8-lead MSOP and SO
n
Battery-Powered Equipment
packages provides for a minimum area solution.
n
Battery Chargers
, LTC and LT are registered trademarks of Linear Technology Corporation.
n
Scanners
Burst Mode is a trademark of Linear Technology Corporation.
TYPICAL APPLICATIO
V
IN
4.5V TO 18V
LTC1771 Efficiency
+
100
R
22F
SENSE
0.05
25V
V = 5V
IN
90
V = 10V
IN
M1
V
IN SENSE
Si6447DQ
L1
RUN/SS PGATE
80
V = 15V
IN
15H
V
C OUT
SS LTC1771
I
TH
3.3V
0.01F
R 70
C 2A
V V
MODE UPS5817 +
FB IN C
OUT
10k
GND
150F
R2
C
C
6.3V
60
1.64M
22OpF
1%
50
R1
V = 3.3V
1M OUT
R = 0.05
SENSE
1%
40
C
FF
1771 F01
0.1 1 10 100 1000 10000
5pF
LOAD CURRENT (mA)
1771 F01b
Figure 1. High Efficiency Step-Down Converter
1
EFFICIENCY (%)
U
ULTC1771
ABSOLUTE AXI U RATI GS
(Note 1)
Input Supply Voltage (V )........................ 0.3V to 20V Junction Temperature (Note 2)............................ 125 C
IN
Peak Driver Output Current < 10m s (PGATE) ............. 1A Operating Temperature Range (Note 3)
RUN/SS Voltage ......................... 0.3V to (V + 0.3V)* LTC1771E......................................... 40 C to 85 C
IN
MODE Voltage .......................................... 0.3V to 20V LTC1771I ......................................... 40 C to 85 C
I , V Voltage .......................................... 0.3V to 5V Storage Temperature Range ................. 65 C to 150 C
TH FB
SENSE Voltage (V > 12V)..(V 12V) to (V + 0.3V)* Lead Temperature (Soldering, 10 sec).................. 300 C
IN IN IN
SENSE Voltage (V 12V) ........ 0.3V to (V + 0.3V)*
IN IN *RUN/SS and SENSE cannot exceed 20V.
UUW
PACKAGE/ORDER I FOR ATIO
ORDER PART
ORDER PART
TOP VIEW
NUMBER NUMBER
TOP VIEW
RUN/SS 1 8 MODE
RUN/SS 1 8 MODE LTC1771EMS8 LTC1771ES8
I 2 7 SENSE
TH
I 2 7 SENSE
TH
LTC1771IS8
V 3 6 V
IN
FB V 3 6 V
FB IN
5 PGATE
GND 4
GND 4 5 PGATE
MS8 PACKAGE
S8 PART MARKING
MS8 PART MARKING
8-LEAD PLASTIC MSOP
S8 PACKAGE
8-LEAD PLASTIC SO
T = 125 C, q = 200 C/ W
JMAX JA
LTKD 1771
T = 125 C, q = 110 C/ W
JMAX JA
1771I
Consult factory for Military grade parts.
ELECTRICAL CHARACTERISTICS
The l denotes specifications which apply over the full operating temperature range, otherwise specifications are T = 25 C.
A
V = 10V, V = open unless otherwise specified.
IN RUN
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
V Feedback Voltage (Note 5) l 1.205 1.230 1.255 V
FB
I Feedback Current (Note 5) l 110 nA
FB
I No-Load Supply Current V = 10V, I = 0 (Note 6) 10 m A
SUPPLY IN LOAD
D V Reference Voltage Line Regulation V = 5V to 15V (Note 5) l 0.003 0.03 %/V
LINEREG IN
D V Output Voltage Load Regulation I = 0.5V to 2V, Burst Disabled (Note 5) l 0.25 1 %
LOADREG TH
I Input DC Supply Current (Note 4)
Q
Active Mode (PGATE = 0V) V = 2.8V to 18V 150 235 m A
IN
Sleep Mode (Note 6) V = 2.8V to 18V, V = 1.5V 9 15 m A
IN FB
Shutdown V = 2.8V to 18V, V = 0V 2 6 m A
IN RUN
Short Circuit V = 2.8V to 18V, V = 0V 175 275 m A
IN FB
D V Maximum Current Sense Threshold V = V 20mV l 110 140 180 mV
SENSE(MAX) FB REF
D V Minimum Current Sense Threshold V = V + 20mV, Burst Disabled 25 mV
SENSE(MIN) FB REF
D V Sleep Current Sense Threshold I = 1V 50 mV
SENSE(SLEEP) TH
t Switch Off Time V at Regulated Value 3 3.5 4 m s
OFF FB
V = 0V 70 m s
FB
V Mode Pin Threshold V Rising l 0.5 1.3 2 V
MODE MODE
2
U WWW