FEATURES
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LTC1877
High Efficiency
Monolithic Synchronous
Step-Down Regulator
DESCRIPTION
The LTC
®
1877 s a high efficiency monolithic synchronous
buck regulator using a constant-frequency, current mode
architecture. Supply current during operation is only 10μA
and drops to < 1μA in shutdown. The 2.65V to 10V input
voltage range makes the LTC1877 ideally suited for both
single and dual Li-Ion battery-powered applications. 100%
duty cycle provides low dropout operation, extending bat-
tery life in portable systems.
Switching frequency is internally set at 550kHz, allowing
the use of small surface mount inductors and capacitors.
For noise sensitive applications the LTC1877 can be exter-
nally synchronized from 400kHz to 700kHz. Burst Mode
operation is inhibited during synchronization or when the
SYNC/MODE pin is pulled low, preventing low frequency
ripple from interfering with audio circuitry.
The internal synchronous switch increases efficiency
and eliminates the need for an external Schottky diode.
Low output voltages are easily supported with the 0.8V
feedback reference voltage. The LTC1877 is available in a
space saving 8-lead MSOP package. Lower input voltage
applications (less than 7V abs max) should refer to the
LTC1878 data sheet.
L,
LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their respective
owners.
High Efficiency: Up to 95%
Very Low Quiescent Current: Only 10μA
During Operation
600mA Output Current at V
IN
= 5V
2.65V to 10V Input Voltage Range
550kHz Constant-Frequency Operation
No Schottky Diode Required
Low Dropout Operation: 100% Duty Cycle
Synchronizable from 400kHz to 700kHz
Selectable Burst Mode
®
Operation or
Pulse-Skipping Mode
0.8V Reference Allows Low Output Voltages
Shutdown Mode Draws < 1μA Supply Current
±2% Output Voltage Accuracy
Current Mode Control for Excellent Line and Load
Transient Response
Overcurrent and Overtemperature Protected
Available in 8-Lead MSOP Package
APPLICATIONS
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Cellular Telephones
Wireless Modems
Personal Information Appliances
Portable Instruments
Distributed Power Systems
Battery-Powered Equipment
TYPICAL APPLICATION
High Efficiency Step-Down Converter
V
IN
2.65V
TO 10V
5
SW
SYNC
6
LTC1877
V
IN
1
RUN
3
2
I
TH
GND V
FB
7
10μF**
CER
4
*TOKO
D62CB A920CY-100M
**TAIYO-YUDEN
CERAMIC LMK325BJ106MN
***SANYO
POSCAP 6TPA47M
†
V
OUT
CONNECTED TO V
IN
FOR 2.65V < V
IN
< 3.3V
10μH*
20pF
VOUT
†
3.3V
47μF***
887k
280k
100
95
90
EFFICIENCY (%)
85
80
75
70
65
60
55
50
0.1
1877 TA01
Efficiency vs Output Current
V
IN
= 3.6V
V
IN
= 10V
V
IN
= 7.2V
V
IN
= 5V
+
220pF
V
OUT
= 3.3V
L = 10μH
Burst Mode OPERATION
1.0
100
10
OUTPUT CURRENT (mA)
1000
1877 TA02
1877fb
1
LTC1877
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TOP VIEW
RUN
I
TH
V
FB
GND
1
2
3
4
8
7
6
5
PLL LPF
SYNC/MODE
V
IN
SW
Input Supply Voltage (V
IN
) ..........................–0.3V to 11V
I
TH
, PLL LPF Voltage ................................. –0.3V to 2.7V
RUN, V
FB
Voltages ...................................... –0.3V to V
IN
SYNC/MODE Voltage .................................. –0.3V to V
IN
SW Voltage ................................... –0.3V to (V
IN
+ 0.3V)
P-Channel MOSFET Source Current (DC)............ 800mA
N-Channel MOSFET Sink Current (DC)................ 800mA
Peak SW Sink and Source Current .......................... 1.5A
Operating Temperature Range (Note 2) .....–40°C to 85°C
Junction Temperature (Note 3) ............................ 125°C
Storage Temperature Range .................. –65°C to 150°C
Lead Temperature (Soldering, 10 sec)................... 300°C
MS8 PACKAGE
8-LEAD PLASTIC MSOP
T
JMAX
= 125°C,
θ
JA
= 150°C/W
ORDER INFORMATION
LEAD FREE FINISH
LTC1877EMS8#PBF
LTC1877IMS8#PBF
TAPE AND REEL
LTC1877EMS8#TRPBF
LTC1877IMS8#TRPBF
PART MARKING
LTLU
LTLV
PACKAGE DESCRIPTION
8-Lead Plastic MSOP
8-Lead Plastic MSOP
TEMPERATURE RANGE
–40°C to 85°C
–40°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
Consult LTC Marketing for information on non-standard lead based finish parts.
For more information on lead free part marking, go to:
http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to:
http://www.linear.com/tapeandreel/
ELECTRICAL CHARACTERISTICS
SYMBOL
I
VFB
V
FB
ΔV
OVL
ΔV
FB
V
LOADREG
V
IN
I
Q
PARAMETER
Feedback Current
Regulated Output Voltage
Output Overvoltage Lockout
Reference Voltage Line Regulation
Output Voltage Load Regulation
Input Voltage Range
Input DC Bias Current
Pulse-Skipping Mode
Burst Mode Operation
Shutdown
Oscillator Frequency
SYNC Capture Range
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 5V unless otherwise specified.
CONDITIONS
(Note 4)
(Note 4) 0°C ≤ T
A
≤ 85°C
(Note 4) –40°C ≤ T
A
≤ 85°C
ΔV
OVL
= V
OVL
– V
FB
V
IN
= 2.65V to 10V (Note 4)
Measured in Servo Loop; V
ITH
= 0.9V to 1.2V
Measured in Servo Loop; V
ITH
= 1.6V to 1.2V
(Note 5)
2.65V < V
IN
< 10V, V
SYNC/MODE
= 0V, I
OUT
= 0A
V
SYNC/MODE
= V
IN
, I
OUT
= 0A
V
RUN
= 0V, V
IN
= 10V
V
FB
= 0.8V
V
FB
= 0V
495
400
l
l
l
l
l
l
MIN
0.784
0.74
20
TYP
4
0.8
0.8
50
0.05
0.1
–0.1
MAX
30
0.816
0.84
110
0.15
0.5
–0.5
10
UNITS
nA
V
V
mV
%/V
%
%
V
μA
μA
μA
kHz
kHz
kHz
2.65
230
10
0
550
80
350
15
1
605
700
f
OSC
f
SYNC
1877fb
2
LTC1877
ELECTRICAL CHARACTERISTICS
SYMBOL
I
PLL LPF
PARAMETER
Phase Detector Output Current
Sinking Capability
Sourcing Capability
R
DS(ON)
of P-Channel MOSFET
R
DS(ON)
of N-Channel MOSFET
Peak Inductor Current
SW Leakage
SYNC/MODE Threshold
SYNC/MODE Leakage Current
RUN Threshold
RUN Input Current
l
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 5V unless otherwise specified.
CONDITIONS
f
PLLIN
< f
OSC
f
PLLIN
> f
OSC
I
SW
= 100mA
I
SW
= –100mA
V
FB
= 0.7V, Duty Cycle < 35%
V
RUN
= 0V, V
SW
= 0V or 8.5V, V
IN
= 8.5V
l
l
l
MIN
3
–3
TYP
10
–10
0.65
0.75
MAX
20
–20
0.85
0.95
1.25
±1
1.5
±1
1.5
±1
UNITS
μA
μA
Ω
Ω
A
μA
V
μA
V
μA
R
PFET
R
NFET
I
PK
I
LSW
V
SYNC/MODE
I
SYNC/MODE
V
RUN
I
RUN
0.8
0.3
0.3
1.0
±0.01
1.0
±0.01
0.7
±0.01
Note 1:
Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2:
The LTC1877E is guaranteed to meet specifications from 0°C to
85°C. Specifications over the –40°C to 85°C operating temperature range
are assured by design, characterization and correlation with statistical
process controls. The LTC1877I is guaranteed over the full –40°C to 85°C
operating temperature range.
Note 3:
T
J
is calculated from the ambient temperature T
A
and power
dissipation P
D
according to the following formulas:
LTC1877EMS8: T
J
= T
A
+ (P
D
)(150°C/W)
Note 4:
The LTC1877 is tested in a feedback loop which servos V
FB
to the
balance point for the error amplifier (V
ITH
= 1.2V).
Note 5:
Dynamic supply current is higher due to the gate charge being
delivered at the switching frequency.
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency vs Input Voltage
100
95
90
EFFICIENCY (%)
85
80
75
70
65
60
55
50
0
2
6
8
4
INPUT VOLTAGE (V)
10
12
1877 G01
Efficiency vs Output Current
100
90
80
EFFICIENCY (%)
V
IN
= 7.2V
V
IN
= 3.6V
V
IN
= 7.2V
EFFICIENCY (%)
V
IN
= 3.6V
95
90
85
80
75
70
65
60
Efficiency vs Output Current
L = 15μH
L = 10μH
I
LOAD
= 100mA I
LOAD
= 10mA
I
LOAD
= 300mA
70
60
50
40
30
20
10
0
0.1
I
LOAD
= 1mA
I
LOAD
= 0.1mA
V
OUT
= 2.5V
L = 10μH
Burst Mode OPERATION
PULSE-SKIPPING MODE
Burst Mode OPERATION
V
OUT
= 2.5V
L = 10μH
1.0
100
10
OUTPUT CURRENT (mA)
1000
1877 G02
55
0.1
V
IN
= 10V
V
OUT
= 3.3V
Burst Mode OPERATION
1.0
100
10
OUTPUT CURRENT (mA)
1000
1877 G03
1877fb
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LTC1877
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency vs Output Current
95
90
85
EFFICIENCY (%)
80
75
70
65
60
55
50
0.1
L = 10μH
V
OUT
= 2.5V
1.0
100
10
OUTPUT CURRENT (mA)
1000
1877 G04
Reference Voltage vs Temperature
0.814
605
V
IN
= 5V
0.809
REFERENCE VOLTAGE (V)
595
585
FREQUENCY (kHz)
575
565
555
545
535
525
0.789
0.784
–50 –25
515
505
50
25
75
0
TEMPERATURE (°C)
100
125
Oscillator Frequency
vs Temperature
V
IN
= 5V
V
IN
= 3.6V
V
IN
= 7.2V
V
IN
= 5V
V
IN
= 10V
0.804
0.799
0.794
495
–50
–25
25
50
75
0
TEMPERATURE (°C)
100
125
1877 G05
1877 G06
Oscillator Frequency
vs Supply Voltage
605
595
OSCILLATOR FREQUENCY (kHz)
585
OUTPUT VOLTAGE (V)
575
565
555
545
535
525
515
505
495
0
2
6
8
4
SUPPLY VOLTAGE (V)
10
12
1877 G07
Output Voltage vs Load Current
2.53
2.52
2.51
2.50
2.49
2.48
2.47
2.46
2.45
2.44
2.43
0
200
600
400
LOAD CURRENT (mA)
800
1877 G08
R
DS(ON)
vs Input Voltage
1.2
1.0
0.8
R
DS(ON)
(Ω)
0.6
MAIN SWITCH
0.4
0.2
0
SYNCHRONOUS
SWITCH
PULSE-SKIPPING MODE
V
IN
= 4.2V
L = 10μH
0
1
2
3 4 5 6 7
INPUT VOLTAGE (V)
8
9
10
1877 G09
R
DS(ON)
vs Temperature
1.4
1.2
DC SUPPLY CURRENT (μA)
1.0
R
DS(ON)
(Ω)
V
IN
= 3V
0.8
V
IN
= 5V
0.6
0.4
0.2
–50 –25
SYNCHRONOUS SWITCH
MAIN SWITCH
50
25
75
0
TEMPERATURE (°C)
100
125
250
DC Supply Current vs Input Voltage
300
PULSE-SKIPPING MODE
200
V
OUT
= 1.8V
150
SUPPLY CURRENT (μA)
250
200
150
100
50
Burst Mode OPERATION
0
0
2
6
4
INPUT VOLTAGE (V)
8
10
1877 G11
DC Supply Current vs Temperature
V
IN
= 5V
PULSE-SKIPPING MODE
100
50
Burst Mode OPERATION
0
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
1877 G10
1877 G11b
1877fb
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LTC1877
TYPICAL PERFORMANCE CHARACTERISTICS
Switch Leakage vs Temperature
1400
1200
SWITCH LEAKAGE (nA)
1000
MAIN SWITCH
800
600
400
200
0
–50 –25
SYNCHRONOUS
SWITCH
V
IN
= 10V
RUN = 0V
SWITCH LEAKAGE (nA)
16
14
12
10
8
6
4
2
50
25
75
0
TEMPERATURE (°C)
100
125
0
0
2
4
MAIN SWITCH
6
INPUT VOLTAGE (V)
8
10
1877 G13
Switch Leakage vs Input Voltage
RUN = 0V
SW
5V/DIV
V
OUT
20mV/DIV
AC COUPLED
Burst Mode Operation
SYNCHRONOUS
SWITCH
I
L
200mA/DIV
1877
G12
V
IN
= 5V
V
OUT
= 1.5V
C
IN
= 10μF
10μs/DIV
L = 10μH
C
OUT
= 47μF
I
LOAD
= 50mA
1877 G14
Start-Up from Shutdown
RUN
5V/DIV
V
OUT
1V/DIV
V
OUT
50mV/DIV
AC COUPLED
Load Step Response
I
L
500mA/DIV
I
L
500mA/DIV
I
TH
1V/DIV
50μs/DIV
V
IN
= 5V
V
OUT
= 1.5V
L = 10μH
1877 G15
C
IN
= 10μF
C
OUT
= 47μF
I
LOAD
= 500mA
V
IN
= 5V
V
OUT
= 1.5V
L = 10μH
40μs/DIV
C
IN
= 10μF
C
OUT
= 47μF
I
LOAD
= 50mA TO 500mA
PULSE-SKIPPING MODE
1877 G16
Load Step Response
Load Step Response
V
OUT
50mV/DIV
AC COUPLED
V
OUT
50mV/DIV
AC COUPLED
I
L
500mA/DIV
10 s/DIV
I
L
500mA/DIV
I
TH
1V/DIV
1877 G17
40μs/DIV
C
IN
= 10μF
C
OUT
= 47μF
I
LOAD
= 50mA TO 500mA
Burst Mode OPERATION
I
TH
1V/DIV
20μs/DIV
C
IN
= 10μF
C
OUT
= 47μF
I
LOAD
= 200mA TO 500mA
PULSE-SKIPPING MODE
1877 G18
V
IN
= 5V
V
OUT
= 1.5V
L = 10μH
V
IN
= 5V
V
OUT
= 1.5V
L = 10μH
1877fb
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