LTC1879
1.2A Synchronous
Step-Down Regulator with
15µA Quiescent Current
FEATURES
s
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DESCRIPTIO
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High Efficiency: Up to 95%
Low Quiescent Current: Only 15µA with No Load
550kHz Constant Frequency Operation
2.65V to 10V Input Voltage Range
V
OUT
from 0.8V to V
IN
, I
OUT
to 1.2A
True PLL Frequency Locking from 350kHz to 750kHz
Power Good Output Voltage Monitor
Low Dropout Operation: 100% Duty Cycle
Burst Mode
®
or Pulse Skipping Operation
Current Mode Operation for Excellent Line and Load
Transient Response
Shutdown Mode Draws < 1µA Supply Current
±2%
Output Voltage Accuracy
Overcurrent and Overtemperature Protected
Available in 16-Lead SSOP Package
The LTC
®
1879 is a high efficiency monolithic synchro-
nous buck regulator using a constant frequency, current
mode architecture. Operating supply current is only 15µA
with no load and drops to < 1µA in shutdown. The input
supply voltage range of 2.65V to 10V makes the LTC1879
ideally suited for both single and dual Li-Ion battery-pow-
ered applications. 100% duty cycle provides low dropout
operation, extending battery life in portable systems.
The switching frequency is internally set to 550kHz, allow-
ing the use of small surface mount inductors and capaci-
tors. For noise sensitive applications, the LTC1879 can be
externally synchronized from 350kHz to 750kHz. Burst
Mode operation is inhibited during synchronization or
when the SYNC/MODE pin is pulled low.
The internal synchronous rectifier switch increases effi-
ciency and eliminates the need for an external Schottky
diode. Low output voltages are easily supported with a
0.8V feedback reference voltage. The LTC1879 is available
in a 16-lead SSOP package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a registered trademark of Linear Technology Corporation.
APPLICATIO S
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Cellular Telephones
Portable Computers
Wireless Modems
TYPICAL APPLICATIO
V
IN
2.65V TO 10V
C
IN
10µF
2
15
High Efficiency Step-Down Converter
13
SV
IN
RUN/SS
PV
IN
8, 9
5, 12
L1
6.2µH
Efficiency vs Output Load Current
100
90
80
V
IN
= 3.6V
EFFICIENCY (%)
SYNC/MODE
SWP
LTC1879
14
6, 11
PGOOD
SWN
150k
47pF
220pF
SGND
1
4
I
TH
PGND
V
FB
7, 10
3
70
V
IN
= 10V
60
50
40
Burst Mode OPERATION
V
OUT
= 3.1V
L = 6.2µH
1
10
100
OUPUT CURRENT (mA)
1000
1879 TA01b
V
OUT
*
3.1V
C
OUT
47µF
28.0k
80.6k
30
0.1
1879 TA01a
C
IN
: TAIYO YUDEN CERAMIC LMK325BJ106MN
C
OUT
: TDK CERAMIC C4532X5ROJ476M
L1: TOKO A921CY6R2M
*V
OUT
CONNECTED TO V
IN
(MINUS SWITCH AND L1 VOLTAGE DROP) FOR 2.65V < V
IN
< 3.1V
U
V
IN
= 7.2V
1879f
U
U
1
LTC1879
ABSOLUTE
MAXIMUM
RATINGS
(Note 1)
PACKAGE/ORDER INFORMATION
TOP VIEW
SGND 1
RUN/SS 2
V
FB
3
I
TH
4
SWP1 5
SWN1 6
PGND1 7
PV
IN1
8
16 PLL_LPF
15 SYNC/MODE
14 PGOOD
13 SV
IN
12 SWP2
11 SWN2
10 PGND2
9
PV
IN2
Input Supply Voltage ................................ – 0.3V to 11V
I
TH
, PLL_LPF Voltages ............................. – 0.3V to 2.7V
RUN/SS, V
FB
Voltages ............................... – 0.3V to V
IN
SYNC/MODE Voltage ................................. – 0.3V to V
IN
(V
PVIN
– V
SWP
) Voltage ............................. – 0.3V to 11V
V
SWN
Voltage ............................................ – 0.3V to 11V
P-Channel Switch Source Current (DC) .................... 2A
N-Channel Switch Sink Current (DC) ........................ 2A
Peak Switching Sink and Source Current ................. 3A
Operating Ambient Temperature Range
(Note 2) ............................................. – 40°C to 85°C
Junction Temperature (Notes 3, 6) ...................... 125°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
ORDER PART
NUMBER
LTC1879EGN
GN PART
MARKING
1879
GN PACKAGE
16-LEAD PLASTIC SSOP
T
JMAX
= 125°C,
θ
JA
= 140°C/ W,
θ
JC
= 40°C/ W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
The
q
denotes specifications which apply over the full operating temperature range, otherwise specifications are T
A
= 25°C.
V
IN
= 5V unless otherwise noted.
SYMBOL
I
VFB
V
FB
∆V
OVL
∆V
UVL
∆V
FB
/V
FB
V
LOADREG
V
IN
I
Q
PARAMETER
Feedback Current
Regulated Output Voltage
Overvoltage Trip Limit with Respect to V
FB
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
q
q
q
q
MIN
0.784
0.740
20
20
TYP
8
0.80
0.80
60
60
0.05
0.1
– 0.1
MAX
60
0.816
0.840
110
110
0.25
0.6
– 0.6
10
UNITS
nA
V
V
mV
mV
%/V
%
%
V
µA
µA
µA
kHz
kHz
kHz
µA
µA
Ω
Ω
A
µA
V
µA
1879f
Undervoltage Trip Limit with Respect to V
FB
∆V
UVL
= V
FB
– V
UVL
Reference Voltage Line Regulation
V
IN
= 2.65V to 10V (Note 4)
Output Voltage Load Regulation
Input Voltage Range
Input DC Bias Current
Pulse Skipping Mode
Burst Mode Operation
Shutdown
SYNC Capture Range
Oscillator Frequency
Phase Detector Output Current
Sinking Capability
Sourcing Capability
R
DS(ON)
of P-Channel FET
R
DS(ON)
of N-Channel FET
Peak Inductor Current
SW Leakage
SYNC/MODE Leakage Current
V
FB
≥
0.7V
V
FB
= 0V
f
PLLIN
< f
OSC
f
PPLIN
> f
SOC
I
SW
= 100mA, V
IN
= 5V
I
SW
= – 100mA, V
IN
= 5V
V
FB
= 0.7V, Duty Cycle < 35%, V
IN
= 5V
V
RUN
= 0V, V
SW
= 0V or 10V, V
IN
= 10V
(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
Measured in Servo Loop, V
ITH
= 0.9V to 1.2V
Measured in Servo Loop, V
ITH
= 1.6V to 1.2V
q
q
q
2.65
270
15
0
350
495
550
80
10
– 10
0.35
0.37
1.8
2.2
±0.01
1.0
±0.01
365
22
1
750
605
f
SYNC
f
OSC
I
PLLLPF
q
q
3
–3
20
– 20
0.45
0.5
2.7
±2.5
1.5
±1
R
PFET
R
NFET
I
PK
I
LSW
I
SYNC/MODE
V
SYNC/MODE
SYNC/MODE Threshold
q
0.2
2
U
W
U
U
W W
W
LTC1879
ELECTRICAL CHARACTERISTICS
The
q
denotes specifications which apply over the full operating temperature range, otherwise specifications are T
A
= 25°C.
V
IN
= 5V unless otherwise noted.
SYMBOL
V
RUN
I
RUN
PARAMETER
RUN Threshold
RUN Input Current
CONDITIONS
V
RUN
Ramping Up
V
RUN
= 0V
q
MIN
0.2
TYP
0.7
±0.01
MAX
1.5
±1
UNITS
V
µA
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
The LTC1879E is guaranteed to meet specified performance from
0°C to 70°C. Specifications over the – 40°C to 85°C operating ambient
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 formula:
LTC1879: T
J
= T
A
+ (P
D
×
140°C/W)
Note 4:
The LTC1879 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.
Note 6:
This IC includes overtemperature protection that is intended to
protect the device during momentary overload conditions. Junction
temperature will exceed 125°C when overtemperature protection is active.
Continuous operation above the specified maximum operating junction
temperature may impair device reliability.
TYPICAL PERFOR A CE CHARACTERISTICS
R
DS(ON)
vs Temperature
0.7
0.6
0.5
R
DS(ON)
(Ω)
0.4
0.3
0.2
0.1
0
–50
495
–50
V
IN
= 10V
V
IN
= 5V
SYNCHRONOUS SWITCH
MAIN SWITCH
V
IN
= 5V
FREQUENCY (kHz)
V
IN
= 10V
575
595
OSCILLATOR FREQUENCY (kHz)
–25
0
25
50
75
TEMPERATURE (°C)
100
125
–25
0
25
50
75
TEMPERATURE (°C)
DC Supply Current
vs Temperature
300
V
IN
= 5V
250
300
250
DC SUPPLY CURRENT (µA)
SUPPLY CURRENT (µA)
PULSE SKIPPING MODE
200
150
100
50
Burst Mode OPERATON
0
–50
150
100
50
Burst Mode OPERATION
0
R
DS(ON)
(Ω)
0
50
TEMPERATURE (°C)
U W
100
1879 G01
Oscillator Frequency
vs Temperature
V
IN
= 5V
600
590
580
570
560
550
540
530
520
510
500
125
Oscillator Frequency
vs Supply Voltage
555
535
515
2
4
6
8
SUPPLY VOLTAGE (V)
10
1879 G03
1879 G02
DC Supply Current
vs Input Voltage
0.6
0.5
PULSE SKIPPING MODE
200
0.4
0.3
0.2
0.1
0
R
DS(ON)
vs Input Voltage
SYNCHRONOUS
SWITCH
MAIN
SWITCH
100
125
0
2
4
6
INPUT VOLTAGE (V)
8
10
1879 G05
2
3
4
8
7
6
5
INPUT VOLTAGE (V)
9
10
1879 G04
1879 G06
1879f
3
LTC1879
TYPICAL PERFOR A CE CHARACTERISTICS
Switch Leakage vs Temperature
20
18
16
V
IN
= 10V
50
45
40
SWITCH LEAKAGE (µA)
SWITCH LEAKAGE (nA)
OUTPUT VOLTAGE (V)
14
12
10
8
6
4
2
0
–50 –25
50
25
0
75
TEMPERATURE (°C)
100
125
SYNCHRONOUS
SWITCH
MAIN SWITCH
Reference Voltage
vs Temperature
804
803
REFERENCE VOLTAGE (mV)
802
EFFICIENCY (%)
V
IN
= 6V
EFFICIENCY (%)
801
800
799
798
797
796
795
794
–50
–25
0
25
50
75
TEMPERATURE (°C)
100
125
Efficiency vs Output Current
100
90
80
V
IN
= 7.2V
V
IN
= 4.2V
EFFICIENCY (%)
70
60
50
40
30
20
10
0
0.1
EFFICIENCY (%)
4
U W
1879 G07
Switch Leakage vs Input Voltage
2.51
RUN = 0V
T
A
= 25°C
2.50
2.49
2.48
2.47
2.46
2.45
2.44
2.43
2.42
SYNCHRONOUS SWITCH
0
2
6
4
INPUT VOLTAGE (V)
8
10
1879 G08
Output Voltage vs Load Current
35
30
25
20
15
10
5
0
MAIN SWITCH
PULSE SKIPPING MODE
V
IN
= 5V
L = 6.2µH
0
200 400 600 800 1000 1200 1400 1600
LOAD CURRENT (mA)
1879 G09
2.41
Efficiency vs Output Current
100
90
80
70
60
50
40
30
0.1
V
IN
= 10V
V
OUT
= 1.8V
L = 6.2µH
Burst Mode OPERATION
10
100
1
OUTPUT CURRENT (mA)
1000
1879 G11
Efficiency vs Output Current
100
90
80
V
IN
= 3.6V
V
IN
= 3.6V
V
IN
= 5V
V
IN
= 7.2V
V
IN
= 5V
70
V
IN
= 7.2V
60
V
IN
= 10V
50
40
30
0.1
V
OUT
= 2.5V
L = 6.2µH
Burst Mode OPERATION
10
100
1
OUTPUT CURRENT (mA)
1000
1879 G12
1879 G10
Efficiency vs Input Voltage
100
100mA
90
1mA
80
70
60
50
10mA
V
IN
= 4.2V
V
IN
= 7.2V
0.1mA
V
OUT
= 3.1V
L = 6.2µH
Burst Mode OPERATION
PULSE SKIPPING MODE
1
10
100
OUTPUT CURRENT (mA)
1000
1879 G13
40
30
2
V
OUT
= 2.5V
L = 6.2µH
Burst Mode OPERATION
4
6
INPUT VOLTAGE (V)
1879 G14
8
10
1879f
LTC1879
TYPICAL PERFOR A CE CHARACTERISTICS
Load Step (Burst Mode Operation)
I
L
1A/DIV
I
L
1A/DIV
I
VIN
500mA/DIV
RUN/SS
1V/DIV
V
OUT
100mV/DIV
V
IN
= 5V
V
OUT
= 2.5V
L = 4.7µH
50µs/DIV
C
IN
= 20µF
C
OUT
= 47µF
I
LOAD
= 50mA to 1200mA
Burst Mode Operation
I
L
200mA/DIV
I
L
200mA/DIV
V
OUT
20mV/DIV
V
OUT
50mV/DIV
SW
5V/DIV
V
IN
= 5V
V
OUT
= 2.5V
L = 4.7µH
25µs/DIV
C
IN
= 20µF
C
OUT
= 47µF
I
LOAD
= 15mA
U W
Load Step
(Pulse Skipping Mode)
Soft-Start with Shorted Output
V
OUT
100mV/DIV
1879 G15
V
IN
= 5V
V
OUT
= 2.5V
L = 4.7µH
50µs/DIV
C
IN
= 20µF
C
OUT
= 47µF
I
LOAD
= 50mA to 1200mA
1879 G16
V
IN
= 5V
V
OUT
= 0V
L = 4.7µH
5ms/DIV
C
IN
= 20µF
C
OUT
= 47µF
I
LOAD
= 0A
1879 G19
Pulse Skipping Mode Operation
SW
5V/DIV
2.5µs/DIV
C
IN
= 20µF
C
OUT
= 47µF
I
LOAD
= 15mA
1879 G18
1879 G17
V
IN
= 5V
V
OUT
= 2.5V
L = 4.7µH
1879f
5
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