LTC1474/LTC1475
Low Quiescent Current
High Efficiency Step-Down
Converters
DESCRIPTION
The LT C
®
1474/LTC1475 series are high efficiency step-
down converters with internal P-channel MOSFET power
switches that draw only 10µA typical DC supply current at
no load while maintaining output voltage. The LTC1474
uses logic-controlled shutdown while the LTC1475 fea-
tures pushbutton on/off.
The low supply current coupled with Burst Mode
TM
opera-
tion enables the LTC1474/LTC1475 to maintain high effi-
ciency over a wide range of loads. These features, along
with their capability of 100% duty cycle for low dropout
and wide input supply range, make the LTC1474/LTC1475
ideal for moderate current (up to 300mA) battery-powered
applications.
The peak switch current is user-programmable with an
optional sense resistor (defaults to 325mA minimum if not
used) providing a simple means for optimizing the design
for lower current applications. The peak current control
also provides short-circuit protection and excellent start-
up behavior. A low-battery detector that remains functional
in shutdown is provided .
The LTC1474/LTC1475 series availability in 8-lead MSOP
and SO packages and need for few additional components
provide for a minimum area solution.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a trademark of Linear Technology Corporation.
FEATURES
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High Efficiency: Over 92% Possible
Very Low Standby Current: 10
µ
A Typ
Available in Space Saving 8-Lead MSOP Package
Internal 1.4Ω Power Switch (V
IN
= 10V)
Wide V
IN
Range: 3V to 18V Operation
Very Low Dropout Operation: 100% Duty Cycle
Low-Battery Detector Functional During Shutdown
Programmable Current Limit with Optional
Current Sense Resistor (10mA to 400mA Typ)
Short-Circuit Protection
Few External Components Required
Active Low Micropower Shutdown: I
Q
= 6µA Typ
Pushbutton On/Off (LTC1475 Only)
3.3V, 5V and Adjustable Output Versions
APPLICATIONS
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Cellular Telephones and Wireless Modems
4mA to 20mA Current Loop Step-Down Converter
Portable Instruments
Battery-Operated Digital Devices
Battery Chargers
Inverting Converters
Intrinsic Safety Applications
TYPICAL APPLICATION
100
V
IN
4V TO 18V
LOW BATTERY OUT
+
10µF
25V
0.1µF
6
7
V
IN
1
SENSE
V
FB
LTC1474-3.3
3
2
LBI
LBO
8
RUN
SW
5
D1
MBR0530
1474/75 F01
V
OUT
3.3V AT 250mA
L1
100µH
EFFICIENCY (%)
LOW BATTERY IN
RUN SHDN
100k
+
100µF
6.3V
GND
4
L1 = SUMIDA CDRH74-101
Figure 1. High Efficiency Step-Down Converter
U
U
U
LTC1474 Efficiency
90
V
IN
= 5V
V
IN
= 10V
80
V
IN
= 15V
70
60
L = 100µH
V
OUT
= 3.3V
R
SENSE
= 0Ω
0.03
0.3
30
3
LOAD CURRENT (mA)
300
1474/75 TA01
50
1
LTC1474/LTC1475
ABSOLUTE
MAXIMUM
RATINGS
Input Supply Voltage (V
IN
).........................– 0.3V to 20V
Switch Current (SW, SENSE) .............................. 750mA
Switch Voltage (SW).............. (V
IN
– 20V) to (V
IN
+ 0.3V)
V
FB
(Adjustable Versions) ..........................– 0.3V to 12V
V
OUT
(Fixed Versions) ................................ –0.3V to 20V
LBI, LBO ....................................................– 0.3V to 20V
RUN, SENSE .................................. – 0.3V to (V
IN
+ 0.3V)
Operating Ambient Temperature Range
Commercial ............................................ 0°C to 70°C
Industrial ............................................ – 40°C to 85°C
Junction Temperature (Note 1) ............................ 125°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
PACKAGE/ORDER INFORMATION
TOP VIEW
TOP VIEW
V
OUT
/V
FB
LBO
LBI
GND
1
2
3
4
8
7
6
5
RUN
V
IN
SENSE
SW
V
OUT
/V
FB
LBO
LBI/OFF
GND
1
2
3
4
TOP VIEW
8
7
6
5
ON
V
IN
SENSE
SW
MS8 PACKAGE
8-LEAD PLASTIC MSOP
MS8 PACKAGE
8-LEAD PLASTIC MSOP
T
JMAX
= 125°C,
θ
JA
= 150°C/ W
T
JMAX
= 125°C,
θ
JA
= 150°C/ W
ORDER PART NUMBER
LTC1474CMS8
LTC1474CMS8-3.3
LTC1474CMS8-5
ORDER PART NUMBER
LTC1475CMS8
LTC1475CMS8-3.3
LTC1475CMS8-5
MS8 PART MARKING
LTBW
LTCR
LTCS
MS8 PART MARKING
LTBK
LTCP
LTCQ
Consult factory for Military grade parts.
2
U
U
W
W W
U
W
TOP VIEW
8 RUN
7 V
IN
6 SENSE
5 SW
V
OUT
/V
FB
1
LBO 2
LBI/OFF 3
GND 4
8 ON
7 V
IN
6 SENSE
5 SW
V
OUT
/V
FB
1
LBO 2
LBI 3
GND 4
S8 PACKAGE
8-LEAD PLASTIC SO
S8 PACKAGE
8-LEAD PLASTIC SO
T
JMAX
= 125°C,
θ
JA
= 110°C/ W
T
JMAX
= 125°C,
θ
JA
= 110°C/ W
ORDER PART NUMBER
LTC1474CS8
LTC1474IS8
LTC1474CS8-3.3
LTC1474CS8-5
LTC1474IS8-3.3
LTC1474IS8-5
S8 PART MARKING
1474
1474I
14743
14745
14743I
14745I
ORDER PART NUMBER
LTC1475CS8
LTC1475IS8
LTC1475CS8-3.3
LTC1475CS8-5
S8 PART MARKING
1475
1475I
14753
14755
LTC1474/LTC1475
ELECTRICAL CHARACTERISTICS
SYMBOL
V
FB
V
OUT
PARAMETER
Feedback Voltage
LTC1474/LTC1475
Regulated Output Voltage
LTC1474-3.3/LTC1475-3.3
LTC1474-5/LTC1475-5
Feedback Current
LTC1474/LTC1475 Only
No Load Supply Current (Note 3)
Output Voltage Line Regulation
Output Voltage Load Regulation
Output Ripple
I
Q
Input DC Supply Current (Note 2)
Active Mode (Switch On)
Sleep Mode (Note 3)
Shutdown
Switch Resistance
Current Comp Max Current Trip Threshold
Current Comp Sense Voltage Trip Threshold
Voltage Comparator Hysteresis
Switch Off-Time
Low Battery Comparator Threshold
Run/ON Pin Threshold
OFF Pin Threshold (LTC1475 Only)
Sink Current into Pin 2
Source Current from Pin 8
Switch Leakage Current
Leakage Current into Pin 3
Leakage Current into Pin 2
T
A
= 25°C, V
IN
= 10V, V
RUN
= open, R
SENSE
= 0, unless otherwise noted.
CONDITIONS
I
LOAD
= 50mA
I
LOAD
= 50mA
q
q
q
q
MIN
1.205
TYP
1.230
MAX
1.255
UNITS
V
3.234
4.900
3.300
5.000
0
10
5
2
50
100
9
6
1.4
3.366
5.100
30
V
V
nA
µA
I
FB
I
SUPPLY
∆V
OUT
I
LOAD
= 0 (Figure 1 Circuit)
V
IN
= 7V to 12V, I
LOAD
= 50mA
I
LOAD
= 0mA to 50mA
I
LOAD
= 10mA
(Exclusive of Driver Gate Charge Current)
V
IN
= 3V to 18V
V
IN
= 3V to 18V
V
IN
= 3V to 18V, V
RUN
= 0V
I
SW
= 100mA
R
SENSE
= 0Ω
R
SENSE
= 1.1Ω
q
20
15
mV
mV
mV
P-P
175
15
12
1.6
85
110
6.0
1.27
1.0
1.0
1.2
1
0.1
0.5
µA
µA
µA
Ω
mA
mA
mV
mV
µs
µs
V
V
V
mA
µA
µA
µA
µA
R
ON
I
PEAK
V
SENSE
V
HYST
t
OFF
V
LBI, TRIP
V
RUN
V
LBI, OFF
I
LBO, SINK
I
RUN, SOURCE
I
SW, LEAK
I
LBI, LEAK
I
LBO, LEAK
325
70
90
3.5
q
400
76
100
5
4.75
65
1.23
0.7
0.7
0.70
0.8
0.015
0
0
V
OUT
at Regulated Value
V
OUT
= 0V
1.16
0.4
0.4
V
LBI
= 0V, V
LBO
= 0.4V
V
RUN
= 0V
V
IN
= 18V, V
SW
= 0V, V
RUN
= 0V
V
LBI
= 18V, V
IN
= 18V
V
LBI
= 2V, V
LBO
= 5V
0.45
0.4
The
q
denotes specifications which apply over the full operating
temperature range.
Note
1:
T
J
is calculated from the ambient temperature T
A
and power
dissipation P
D
according to the following formulas:
LTC1474CS8/LTC1475CS8: T
J
= T
A
+ (P
D
• 110°C/W)
LTC1474CMS8/LTC1475CMS8: T
J
= T
A
+ (P
D
• 150°C/W)
Note 2:
Dynamic supply current is higher due to the gate charge being
delivered at the switching frequency. See Applications Information.
Note 3:
No load supply current consists of sleep mode DC current (9µA
typical) plus a small switching component (about 1µA for Figure 1 circuit)
necessary to overcome Schottky diode and feedback resistor leakage.
3
LTC1474/LTC1475
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency vs Input Voltage
100
95
FIGURE 1 CIRCUIT
L: CDRH73-101
40
30
20
FIGURE 1 CIRCUIT
I
LOAD
= 100mA
EFFICIENCY (%)
90
85
80
∆V
OUT
(mV)
∆V
OUT
(mV)
I
LOAD
= 25mA
I
LOAD
= 200mA
I
LOAD
= 1mA
75
70
–10
–20
0
4
12
8
INPUT VOLTAGE (V)
Current Trip Threshold vs
Temperature
500
V
IN
= 10V
5
CURRENT TRIP THRESHOLD (mA)
400
R
SENSE
= 0Ω
300
3
SUPPLY CURRENT (µA)
R
DS(ON)
(Ω)
200
R
SENSE
= 1.1Ω
100
0
0
20
40
TEMPERATURE (°C)
60
Switch Leakage Current vs
Temperature
1.0
V
IN
= 18V
LEAKAGE CURRENT (µA)
0.8
SUPPLY CURRENT (µA)
100
120
0.6
OFF-TIME (µs)
0.4
0.2
0
0
20
40
60
TEMPERATURE (°C)
4
U W
16
1474/75 G01
Line Regulation
40
30
20
10
Load Regulation
FIGURE 1 CIRCUIT
R
SENSE
= 0Ω
V
IN
= 15V
10
R
SENSE
= 0.33Ω
0
V
IN
= 10V
0
–10
–20
–30
V
IN
= 5V
0
4
12
8
INPUT VOLTAGE (V)
16
1474/75 G02
0
50
150
200
100
LOAD CURRENT (mA)
250
300
1474/75 G03
Switch Resistance vs
Input Voltage
10.0
Supply Current in Shutdown
4
7.5
5.0
2
T = 70°C
1
2.5
T = 25°C
0
80
1474/75 G04
0
0
5
10
INPUT VOLTAGE (V)
1474/75 G05
15
20
0
5
10
INPUT VOLTAGE (V)
15
20
1474/75 G06
V
IN
DC Supply Current
80
ACTIVE MODE
Off-Time vs Output Voltage
V
IN
= 10V
60
80
60
40
40
20
20
0
SLEEP MODE
0
0
4
12
8
INPUT VOLTAGE (V)
16
20
80
100
1474/75 G07
0
40
100
20
60
80
% OF REGULATED OUTPUT VOLTAGE (%)
1474/75 G09
1474/75 G08
LTC1474/LTC1475
PIN FUNCTIONS
V
OUT
/V
FB
(Pin 1):
Feedback of Output Voltage. In the fixed
versions, an internal resistive divider divides the output
voltage down for comparison to the internal 1.23V refer-
ence. In the adjustable versions, this divider must be
implemented externally.
LBO (Pin 2):
Open Drain Output of the Low Battery
Comparator. This pin will sink current when Pin 3 is below
1.23V.
LBI/OFF (Pin 3):
Input to Low Battery Comparator. This
input is compared to the internal 1.23V reference. For the
LTC1475, a momentary ground on this pin puts regulator
in shutdown mode.
GND (Pin 4):
Ground Pin.
SW (Pin 5):
Drain of Internal PMOS Power Switch. Cath-
ode of Schottky diode must be closely connected to this
pin.
SENSE (Pin 6):
Current Sense Input for Monitoring Switch
Current and Source of Internal PMOS Power Switch.
Maximum switch current is programmed with a resistor
between SENSE and V
IN
pins.
V
IN
(Pin 7):
Main Supply Pin.
RUN/ON (Pin 8):
On LTC1474, voltage level on this pin
controls shutdown/run mode (ground = shutdown, open/
high = run). On LTC1475, a momentary ground on this pin
puts regulator in run mode. A 100k series resistor must be
used between Pin 8 and the switch or control voltage.
FUNCTIONAL DIAGRA
LBI/OFF
1µA
LTC1474: RUN 8
LTC1475: ON
4.75µs
1-SHOT
TRIGGER
OUT
SW
5
V
OUT
1×
20×
STRETCH WAKEUP
LBO
2
+
LB
–
READY
3
LTC1474: LBI
LTC1475: LBI/OFF
×
CONNECTION NOT PRESENT IN LTC1474 SERIES
CONNECTION PRESENT IN LTC1474 SERIES ONLY
W
U
U
U
U
U
100mV
V
IN
7
R
SENSE
(OPTIONAL)
V
CC
–
×
C
ON
+
V
IN
+
–
V
ON
6
SENSE
5Ω
+
+
1.23V
1.23V
REFERENCE
4
GND
1M
3M
(5V VERSION)
1.68M
(3.3V VERSION)
V
OUT
/V
FB
1
OUTPUT DIVIDER IS
IMPLEMENTED EXTERNALLY IN
ADJUSTABLE VERSIONS
1474/75 FD
5
电源技术
