LTC1878
High Efficiency
Monolithic Synchronous
Step-Down Regulator
FEATURES
s
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DESCRIPTIO
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High Efficiency: Up to 95%
Very Low Quiescent Current: Only 10
µ
A
During Operation
600mA Output Current at V
IN
= 3.3V
2.65V to 6V Input Voltage Range
550kHz Constant Frequency Operation
Synchronizable from 400kHz to 700kHz
Selectable Burst Mode
TM
Operation or
Pulse Skipping Mode
No Schottky Diode Required
Low Dropout Operation: 100% Duty Cycle
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
The LTC
®
1878 is a high efficiency monolithic synchro-
nous 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
6V input voltage range makes the LTC1878 ideally suited
for single Li-Ion battery-powered applications. 100% duty
cycle provides low dropout operation, extending battery
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 LTC1878 can be
externally 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 feed-
back reference voltage. The LTC1878 is available in a
space saving 8-lead MSOP package.
For higher input voltage (11V abs max) applications, refer
to the LTC1877 data sheet.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a trademark of Linear Technology Corporation.
APPLICATIO S
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Cellular Telephones
Wireless Modems
Personal Information Appliances
Portable Instruments
Distributed Power Systems
Battery-Powered Equipment
TYPICAL APPLICATIO
V
IN
2.65V
TO 6V
22µF**
CER
7
6
1
2
220pF
5
Efficiency vs Output Load Current
100
95
EFFICIENCY (%)
90
V
IN
= 4.2V
85
V
IN
= 6V
80
75
1878 TA01
High Efficiency Step-Down Converter
10µH*
20pF
SYNC
V
IN
RUN
I
TH
GND V
FB
4
3
SW
V
OUT
†
3.3V
LTC1878
887k
280k
+
47µF***
*TOKO D62CB A920CY-100M
**TAIYO-YUDEN CERAMIC JMK325BJ226MM
***SANYO POSCAP 6TPA47M
†
V
OUT
CONNECTED TO V
IN
FOR 2.65V < V
IN
< 3.3V
70
0.1
U
V
IN
= 3.6V
Burst Mode OPERATION
V
OUT
= 3.3V
L = 10µH
1
10
100
OUTPUT CURRENT (mA)
1000
1878 TA02
U
U
1
LTC1878
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
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 7V
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 Ambient 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
ORDER PART
NUMBER
LTC1878EMS8
MS8 PART MARKING
LTNX
MS8 PACKAGE
8-LEAD PLASTIC MSOP
T
JMAX
= 125°C,
θ
JA
= 150°C/ W
Consult factory for Industrial and 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
= 3.6V unless otherwise specified.
SYMBOL
I
VFB
V
FB
∆V
OVL
∆V
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
Phase Detector Output Current
Sinking Capability
Sourcing Capability
R
DS(ON)
of P-Channel MOSFET
R
DS(ON)
of N-Channel MOSFET
f
PLLIN
< f
OSC
f
PLLIN
> f
OSC
I
SW
= 100mA
I
SW
= –100mA
q
q
CONDITIONS
(Note 4)
(Note 4) 0°C
≤
T
A
≤
85°C
(Note 4) – 40°C
≤
T
A
≤
85°C
∆V
OVL
= V
OVL
– V
FB
V
IN
= 2.65V to 6V (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
< 6V, V
SYNC/MODE
= 0V, I
OUT
= 0A
V
SYNC/MODE
= V
IN
, I
OUT
= 0A
V
RUN
= 0V, V
IN
= 6V
V
FB
= 0.8V
V
FB
= 0V
q
q
q
q
q
q
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
0.2
0.5
– 0.5
6
UNITS
nA
V
V
mV
%/V
%
%
V
µA
µA
µA
kHz
kHz
kHz
µA
µA
Ω
Ω
2.65
230
10
0
495
400
3
–3
10
–10
0.5
0.6
550
80
350
15
1
605
700
20
–20
0.7
0.8
f
OSC
f
SYNC
I
PLL LPF
R
PFET
R
NFET
2
U
W
U
U
W W
W
LTC1878
ELECTRICAL CHARACTERISTICS
The
q
denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C.
V
IN
= 3.6V unless otherwise specified.
SYMBOL
I
PK
I
LSW
I
SYNC/MODE
V
RUN
I
RUN
PARAMETER
Peak Inductor Current
SW Leakage
SYNC/MODE Leakage Current
RUN Threshold
RUN Input Current
V
RUN
Rising
q
CONDITIONS
V
IN
= 3.3V, V
FB
= 0.7V, Duty Cycle < 35%
V
RUN
= 0V, V
SW
= 0V or 6V, V
IN
= 6V
V
SYNC/MODE
Rising
q
MIN
0.8
0.3
0.3
TYP
1.0
±0.01
1.0
±0.01
0.7
±0.01
MAX
1.25
±1
1.5
±1
1.5
±1
UNITS
A
µA
V
µA
V
µA
V
SYNC/MODE
SYNC/MODE Threshold
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
The LTC1878E 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.
Note 3:
T
J
is calculated from the ambient temperature T
A
and power
dissipation P
D
according to the following formulas:
LTC1878EMS8: T
J
= T
A
+ (P
D
)(150°C/W)
Note 4:
The LTC1878 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 PERFOR A CE CHARACTERISTICS
Efficiency vs Input Voltage
100
95
90
I
LOAD
= 100mA
I
LOAD
= 10mA
EFFICIENCY (%)
EFFICIENCY (%)
85
80
I
LOAD
= 1mA
I
LOAD
= 0.1mA
60
50
40
30
V
IN
= 3.6V
V
IN
= 4.2V
EFFICIENCY (%)
I
LOAD
= 300mA
75
70
Burst Mode OPERATION
65 V
OUT
= 2.5V
L = 10µH
60
3
4
6
2
5
INPUT VOLTAGE (V)
U W
7
8
1878 G01
Efficiency vs Output Current
100
90
80
70
V
IN
= 3.6V
V
IN
= 4.2V
Efficiency vs Output Current
95
90
85
80
75
70
65
60
55
Burst Mode OPERATION
V
IN
= 6V
V
OUT
= 2.5V
1
10
100
OUTPUT CURRENT (mA)
1000
1878 G03
L = 15µH
L = 10µH
20
10
0
0.1
PULSE SKIPPING MODE
Burst Mode OPERATION
V
OUT
= 1.8V
L = 10µH
1
10
100
OUTPUT CURRENT (mA)
1000
1878 G02
50
0.1
3
LTC1878
TYPICAL PERFOR A CE CHARACTERISTICS
Efficiency vs Output Current
95
90
EFFICIENCY (%)
0.814
V
IN
= 3V
REFERENCE VOLTAGE (V)
85
80
75
70
65
0.1
V
IN
= 3.6V
V
IN
= 4.2V
V
IN
= 6V
0.804
0.799
0.794
0.789
FREQUENCY (kHz)
V
OUT
= 1.8V
L = 10µH
10
100
1
OUTPUT CURRENT (mA)
1000
1878 G04
Oscillator Frequency
vs Supply Voltage
605
595
1.83
1.82
OUTPUT VOLTAGE (V)
OSCILLATOR FREQUENCY (kHz)
585
575
565
555
545
535
525
515
505
495
0
2
4
SUPPLY VOLTAGE (V)
1878 G07
R
DS(ON)
(Ω)
6
R
DS(ON)
vs Temperature
1.2
1.1
1.0
0.9
R
DS(ON)
(Ω)
SYNCHRONOUS SWITCH
MAIN SWITCH
DC SUPPLY CURRENT (µA)
SUPPLY CURRENT (µA)
0.8
0.7
0.6
0.5
0.4
0.3
–50
V
IN
= 3V
V
IN
= 5V
–25
0
25
50
75
TEMPERATURE (°C)
4
U W
8
Reference Voltage
vs Temperature
V
IN
= 3.6V
605
595
585
575
565
555
545
535
525
515
505
0.784
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
Oscillator Frequency
vs Temperature
V
IN
= 3.6V
0.809
495
–50
–25
25
50
75
0
TEMPERATURE (°C)
100
125
1878 G05
1878 G06
Output Voltage vs Load Current
0.9
0.8
0.7
1.81
1.80
1.79
1.78 PULSE SKIPPING MODE
V
IN
= 3.6V
L = 10µH
1.77
0 100 200 300 400 500 600 700 800 900
LOAD CURRENT (mA)
1878 G08
R
DS(ON)
vs Input Voltage
SYNCHRONOUS
SWITCH
0.6
0.5
0.4
0.3
0.2
0.1
0
0
1
2
3
5
6
4
INPUT VOLTAGE (V)
7
8
MAIN
SWITCH
1878 G09
DC Supply Current
vs Input Voltage
250
V
OUT
= 1.8V
PULSE SKIPPING
MODE
300
250
200
150
100
50
DC Supply Current
vs Temperature
V
IN
= 3.6V
200
150
PULSE SKIPPING
MODE
100
50
Burst Mode
OPERATION
0
Burst Mode
OPERATION
–25
50
25
75
0
TEMPERATURE (°C)
100
125
100
125
0
1
4
3
2
5
INPUT VOLTAGE (V)
6
7
1878 G11
0
–50
1878 G10
1878 G12
LTC1878
TYPICAL PERFOR A CE CHARACTERISTICS
Switch Leakage vs Temperature
2.5
V
IN
= 7V
RUN = 0V
2.0
SWITCH LEAKAGE (µA)
SWITCH LEAKAGE (nA)
1.5
1.0
MAIN
SWITCH
SYNCHRONOUS
SWITCH
0.5
0
– 50 – 25
0
75
50
25
TEMPERATURE (°C)
Pulse Skipping Mode Operation
SW
5V/DIV
V
OUT
20mV/DIV
AC
COUPLED
I
L
200mA/DIV
1µs/DIV
V
IN
= 4.2V
C
IN
= 22µF
V
OUT
= 1.5V C
OUT
= 47µF
L = 10µH
I
LOAD
= 50mA
Load Step Response
V
OUT
100mV/DIV
AC
COUPLED
I
L
500mA/DIV
I
TH
1V/DIV
40µs/DIV
V
IN
= 3.6V
C
IN
= 22µF
V
OUT
= 1.5V C
OUT
= 47µF
L = 10µH
I
LOAD
= 50mA TO 500mA
PULSE SKIPPING MODE
U W
100
1878 G13
Switch Leakage vs Input Voltage
1.2
1.0
SYNCHRONOUS
SWITCH
0.8
0.6
0.4
0.2
0
125
V
OUT
50mV/DIV
AC
COUPLED
Burst Mode Operation
RUN = 0V
SW
5V/DIV
MAIN
SWITCH
I
L
200mA/DIV
0
1
2
5
6
3
4
INPUT VOLTAGE (V)
7
8
1878 G20
10µs/DIV
V
IN
= 4.2V
C
IN
= 22µF
V
OUT
= 1.5V C
OUT
= 47µF
L = 10µH
I
LOAD
= 50mA
1878 G14
Start-Up from Shutdown
Load Step Response
RUN
2V/DIV
V
OUT
1V/DIV
V
OUT
50mV/DIV
AC
COUPLED
I
L
500mA/DIV
I
L
500mA/DIV
I
TH
1V/DIV
1878 G15
40µs/DIV
C
IN
= 22µF
V
IN
= 3.6V
V
OUT
= 1.5V C
OUT
= 47µF
L = 10µH
I
LOAD
= 500mA
1878 G16
40µs/DIV
V
IN
= 3.6V
C
IN
= 22µF
V
OUT
= 1.5V C
OUT
= 47µF
L = 10µH
I
LOAD
= 200mA TO 500mA
PULSE SKIPPING MODE
1878 G17
Load Step Response
V
OUT
100mV/DIV
AC
COUPLED
I
L
500mA/DIV
I
TH
1V/DIV
40µs/DIV
V
IN
= 3.6V
C
IN
= 22µF
V
OUT
= 1.5V C
OUT
= 47µF
L = 10µH
I
LOAD
= 50mA TO 500mA
Burst Mode OPERATION
1878 G18
1878 G19
5
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