LTC1771
10µA Quiescent Current
High Efficiency Step-Down
DC/DC Controller
FEATURES
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DESCRIPTIO
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Very Low Standby Current: 10µA
Available in Space-Saving 8-Lead MSOP Package
Output Currents: Up to 5A
Wide V
IN
Range: 2.8V to 20V Operation
V
OUT
Range: 1.23V to 18V
High Efficiency: Over 93% Possible
±2%
Output Accuracy
Very Low Dropout Operation: 100% Duty Cycle
Current Mode Operation for Excellent Line and
Load Transient Response
Defeatable Burst Mode
TM
Operation
Short-Circuit Protected
Optional Programmable Soft-Start
Micropower Shutdown: I
Q
= 2µA
The LTC
®
1771 is a high efficiency current mode step-
down DC/DC controller that draws as little as 10µA DC
supply current to regulate the output at no load while
maintaining high efficiency for loads up to several amps.
The LTC1771 drives an external P-channel power MOSFET
using a current mode, constant off-time architecture. An
external sense resistor is used to program the operating
current level. Current mode control provides short-circuit
protection, excellent transient response and controlled
start-up behavior. Burst Mode operation enables the
LTC1771 to maintain high efficiency down to extremely
low currents. Shutdown mode further reduces the supply
current to a mere 2µA. For low noise applications, Burst
Mode operation can be easily disabled with the MODE pin.
Wide input supply range of 2.8V to 18V (20V maximum)
and 100% duty cycle operation for low dropout make the
LTC1771 ideal for a wide variety of battery-powered appli-
cations where maximizing battery life is important.
The LTC1771’s availability in both 8-lead MSOP and SO
packages provides for a minimum area solution.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a trademark of Linear Technology Corporation.
APPLICATIO S
s
s
s
s
s
s
Cellular Telephones and Wireless Modems
1- to 4-Cell Lithium-Ion-Powered Applications
Portable Instruments
Battery-Powered Equipment
Battery Chargers
Scanners
TYPICAL APPLICATIO
V
IN
4.5V TO 18V
R
SENSE
0.05Ω
V
IN
RUN/SS
C
SS
0.01µF
R
C
10k
C
C
22OpF
SENSE
PGATE
M1
Si6447DQ
+
22µF
25V
100
V
IN
= 5V
90
EFFICIENCY (%)
I
TH
LTC1771
V
FB
MODE
GND
V
IN
R2
1.64M
1%
L1
15µH
UPS5817
80
70
60
50
40
0.1
V
OUT
= 3.3V
R
SENSE
= 0.05Ω
1
+
C
OUT
150µF
6.3V
V
OUT
3.3V
2A
R1
1M
1%
C
FF
5pF
1771 F01
Figure 1. High Efficiency Step-Down Converter
U
LTC1771 Efficiency
V
IN
= 10V
V
IN
= 15V
10
100
1000
LOAD CURRENT (mA)
10000
1771 F01b
U
U
1
LTC1771
ABSOLUTE
AXI U
RATI GS
(Note 1)
Junction Temperature (Note 2) ............................ 125°C
Operating Temperature Range (Note 3)
LTC1771E ......................................... – 40°C to 85°C
LTC1771I ......................................... – 40°C to 85°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
*RUN/SS and SENSE cannot exceed 20V.
Input Supply Voltage (V
IN
)........................ – 0.3V to 20V
Peak Driver Output Current < 10µs (PGATE) ............. 1A
RUN/SS Voltage ......................... – 0.3V to (V
IN
+ 0.3V)*
MODE Voltage .......................................... – 0.3V to 20V
I
TH
, V
FB
Voltage .......................................... – 0.3V to 5V
SENSE Voltage (V
IN
> 12V)..(V
IN
– 12V) to (V
IN
+ 0.3V)*
SENSE Voltage (V
IN
≤
12V) ........ – 0.3V to (V
IN
+ 0.3V)*
PACKAGE/ORDER I FOR ATIO
TOP VIEW
RUN/SS
I
TH
V
FB
GND
1
2
3
4
8
7
6
5
MODE
SENSE
V
IN
PGATE
ORDER PART
NUMBER
LTC1771EMS8
MS8 PART MARKING
LTKD
RUN/SS 1
I
TH
2
V
FB
3
GND 4
MS8 PACKAGE
8-LEAD PLASTIC MSOP
T
JMAX
= 125°C,
θ
JA
= 200°C/ W
Consult factory for Military grade parts.
ELECTRICAL CHARACTERISTICS
The
q
denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C.
V
IN
= 10V, V
RUN
= open unless otherwise specified.
SYMBOL
V
FB
I
FB
I
SUPPLY
∆V
LINEREG
∆V
LOADREG
I
Q
PARAMETER
Feedback Voltage
Feedback Current
No-Load Supply Current
Reference Voltage Line Regulation
Output Voltage Load Regulation
Input DC Supply Current
Active Mode (PGATE = 0V)
Sleep Mode (Note 6)
Shutdown
Short Circuit
Maximum Current Sense Threshold
Minimum Current Sense Threshold
Sleep Current Sense Threshold
Switch Off Time
Mode Pin Threshold
CONDITIONS
(Note 5)
(Note 5)
V
IN
= 10V, I
LOAD
= 0 (Note 6)
V
IN
= 5V to 15V (Note 5)
I
TH
= 0.5V to 2V, Burst Disabled (Note 5)
(Note 4)
V
IN
= 2.8V to 18V
V
IN
= 2.8V to 18V, V
FB
= 1.5V
V
IN
= 2.8V to 18V, V
RUN
= 0V
V
IN
= 2.8V to 18V, V
FB
= 0V
V
FB
= V
REF
– 20mV
V
FB
= V
REF
+ 20mV, Burst Disabled
I
TH
= 1V
V
FB
at Regulated Value
V
FB
= 0V
V
MODE
Rising
q
q
q
q
q
q
∆V
SENSE(MAX)
∆V
SENSE(MIN)
∆V
SENSE(SLEEP)
t
OFF
V
MODE
2
U
U
W
W W
U
W
TOP VIEW
8
7
6
5
MODE
SENSE
V
IN
PGATE
ORDER PART
NUMBER
LTC1771ES8
LTC1771IS8
S8 PART MARKING
1771
1771I
S8 PACKAGE
8-LEAD PLASTIC SO
T
JMAX
= 125°C,
θ
JA
= 110°C/ W
MIN
1.205
TYP
1.230
1
10
0.003
0.25
150
9
2
175
MAX
1.255
10
0.03
1
235
15
6
275
180
UNITS
V
nA
µA
%/V
%
µA
µA
µA
µA
mV
mV
mV
110
140
– 25
50
3
0.5
3.5
70
1.3
4
2
µs
µs
V
LTC1771
ELECTRICAL CHARACTERISTICS
The
q
denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C.
V
IN
= 10V, V
RUN
= open unless otherwise specified.
SYMBOL
V
RUN/SS
I
RUN
PGATE t
r
, t
f
PARAMETER
RUN/SS Pin Threshold
Source Current
PGATE Transition Time (Note 7)
Rise Time
Fall Time
CONDITIONS
V
RUN/SS
Rising
V
RUN
= 0V, V
IN
= 2.8V to 18V
C
LOAD
= 2000pF
C
LOAD
= 2000pF
q
MIN
0.5
0.3
TYP
1.0
1
70
70
MAX
2
3
140
140
UNITS
V
µA
ns
ns
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
T
J
is calculated from the ambient temperature T
A
and power
dissipation P
D
according to the following formulas:
LTC1771S8: T
J
= T
A
+ (P
D
)(110°C/W)
LTC1771MS8: T
J
= T
A
+ (P
D
)(150°C/W)
Note 3:
The LTC1771E is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the – 40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls. The LTC1771I is guaranteed and tested
over the – 40°C to 85°C operating temperature range.
Note 4:
Dynamic supply current is higher due to the gate charge being
delivered at the switching frequency. See Applications Information.
Note 5:
The LTC1771 is tested in a feedback loop that servos V
FB
to the
balance point for the error amplifier (V
ITH
= 1.23V).
Note 6:
No-load supply current consists of sleep mode current (9µA
typical) plus a small switching component necessary to overcome
Schottky diode leakage and feedback resistor current.
Note 7:
t
r
and t
f
are measured at 10% to 90% levels.
TYPICAL PERFOR A CE CHARACTERISTICS
Efficiency vs Input Voltage
100
100
FIGURE 1 CIRCUIT
90
EFFICIENCY (%)
EFFICIENCY (%)
I
LOAD
= 1A
I
LOAD
= 50mA
80
I
LOAD
= 1mA
70
50
40
30
20
10
Burst Mode OPERATION
DISABLED
∆V
OUT
(%)
60
2
4
6
8 10 12 14 16
INPUT VOLTAGE (V)
18
20
U W
1771 G01
Efficiency vs Load Current
90
80
70
60
Burst Mode OPERATION
ENABLED
Line Regulation
0.4
0.3
0.2
0.1
0
– 0.1
– 0.2
I
LOAD
= 1A
I
LOAD
= 100mA
FIGURE 1 CIRCUIT
0
0.1
V
IN
= 10V
FIGURE 1 CIRCUIT
1
10
100
LOAD CURRENT (mA)
1000
1771 G02
– 0.3
– 0.4
0
5
10
INPUT VOLTAGE (V)
1771 G03
15
20
3
LTC1771
TYPICAL PERFOR A CE CHARACTERISTICS
Load Regulation
0.4
0.2
0
ACTIVE MODE QUIESCENT CURRENT (µA)
FIGURE 1 CIRCUIT
Burst Mode OPERATION
DISABLED
V
IN
= 15V
Burst Mode
OPERATION
ENABLED
SLEEP QUIESCENT CURRENT (µA)
∆V
OUT
(%)
–0.2
–0.4
–0.6
–0.8
–1.0
0
0.5
1.0
LOAD CURRENT (A)
1771 G04
1.5
Shutdown Quiescent Current
vs Input Voltage
8
5
SHUTDOWN QUIESCENT CURRENT (µA)
CURRENT SENSE VOLTAGE (mV)
6
T
A
= –50°C
4
T
A
= 25°C
2
T
A
= 100°C
0
SOFT-START CURRENT (µA)
0
2
4
6 8 10 12 14 16 18 20
INPUT VOLTAGE (V)
1771 G07
Reference Voltage
vs Temperature
1.25
V
IN
= 10V
V
OUT
100mV/DIV
REFERENCE VOLTAGE (V)
1.24
1.23
1.22
50µs/DIV
V
IN
= 10V
V
OUT
= 3.3V
I
LOAD
= 100mA TO 2A
FIGURE 1 CIRCUIT
1771 G11
1.21
–50
–25
0
25
50
TEMPERATURE (°C)
4
U W
V
IN
= 5V
Active Mode Quiescent Current
vs Input Voltage
200
T
A
= 100°C
150
T
A
= –50°C
100
T
A
= 25°C
Sleep Quiescent Current
vs Input Voltage
12
10
8
6
4
2
0
T
A
= –50°C
T
A
= 100°C
T
A
= 25°C
50
0
2.0
0
2
4
6 8 10 12 14 16 18 20
INPUT VOLTAGE (V)
1771 G05
0
2
4
6 8 10 12 14 16 18 20
INPUT VOLTAGE (V)
1771 G06
Run/SS Current vs Input Voltage
200
Current Sense Voltage
vs Temperature
V
IN
= 10V
MAXIMUM
T
A
= –50°C
4
150
3
T
A
= 25°C
100
BURST THRESHOLD
2
50
1
T
A
= 100°C
0
MINIMUM
–50
–50
0
0
2
4
6 8 10 12 14 16 18 20
INPUT VOLTAGE (V)
1771 G08
–25
0
25
50
TEMPERATURE (°C)
75
100
1771 G09
Load Step Transient Response
Burst Mode Operation
V
OUT
50mV/DIV
INDUCTOR
CURRENT
1A/DIV
INDUCTOR
CURRENT
0.5A/DIV
75
100
1771 G10
10µs/DIV
V
IN
= 10V
V
OUT
= 3.3V
I
LOAD
= 100mA
FIGURE 1 CIRCUIT
1771 G12
LTC1771
PI FU CTIO S
RUN/SS (Pin 1):
The voltage level on this pin controls
shutdown/run mode (ground = shutdown, open/high =
run). Connecting an external capacitor to this pin provides
soft-start.
I
TH
(Pin 2):
Error Amplifier Compensation Point. The
current comparator threshold increases with this control
voltage. Nominal voltage range for this pin is 0V to 3V.
V
FB
(Pin 3):
Feedback of Output Voltage for Comparison
to Internal 1.23V Reference. An external resistive divider
across the output is returned to this pin.
GND (Pin 4):
Ground Pin.
PGATE (Pin 5):
High Current Gate Driver for External
P-Channel MOSFET Switch. Voltage swing is from ground
to V
IN
.
V
IN
(Pin 6):
Main Input Voltage Supply Pin.
SENSE (Pin 7):
Current Sense Input for Monitoring Switch
Current. Maximum switch current and Burst Mode
threshold is programmed with an external resistor be-
tween SENSE and V
IN
.
MODE (Pin 8):
Burst Mode Enable/Disable Pin. Connect-
ing this pin to V
IN
(or above 2V) enables Burst Mode
operation, while connecting this pin to ground disables
Burst Mode operation. Do not leave floating.
FUNCTIONAL BLOCK DIAGRA
V
IN
1µA
RUN/SS
1
MODE
8
(BURST ENABLE)
C
SS
1.23V
+
EA
–
V
OUT
10% CURRENT
SLEEP
*
I
TH
2
R
C
C
C
GND
4
1V
2V
1V
–
+
B
READY
V
IN
BLANKING
MODE
ON TRIGGER
1-SHOT
3.5µs
STRETCH
V
FB
3
R1
R2
*
OPTIONAL FOR FOLDBACK
CURRENT LIMITING
+
ON
C
–
ON
SOFT-START
W
U
U
U
U
U
V
IN
6
READY
1.23V
REFERENCE
22k
R
SENSE
+
V
IN
C
IN
10% CURRENT
SENSE
7
250k
PGATE
5
D1
L
V
OUT
+
C
OUT
1771 BD
5
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