LTC1875
15µA Quiescent Current
1.5A Monolithic Synchronous
Step-Down Regulator
FEATURES
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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 6V Input Voltage Range
V
OUT
from 0.8V to V
IN
, I
OUT
to 1.5A
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
®
1875 is a high efficiency 1.5A monolithic syn-
chronous 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 6V makes the
LTC1875 ideally suited for single Li-Ion battery-powered
applications. 100% duty cycle provides low dropout op-
eration, 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 LTC1875 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 switch increases efficiency and
eliminates the need for an external Schottky diode. Low
output voltages are easily supported with a 0.8V feedback
reference voltage. The LTC1875 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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Portable Computers
Portable Instruments
Wireless Modems
TYPICAL APPLICATIO
V
IN
2.65V TO 6V
C
IN
22µF
High Efficiency Step-Down Converter
Efficiency vs Output Load Current
100
SV
IN
RUN/SS
PV
IN
EFFICIENCY (%)
SYNC/MODE SWP
LTC1875
PGOOD
SWN
150k
I
TH
47pF
220pF
SGND
PGND
88.7k
V
FB
28.0k
1875 TA01
95
90
L1
6.8µH
85
80
75
70
65
60
55
0.1
V
OUT
*
3.3V
+
C
OUT
47µF
C
IN
: TAIYO YUDEN CERAMIC JMK325BJ226MM
C
OUT
: SANYO POSCAP 6TPA47M
L1: TOKO 646CY-6R8M
*V
OUT
CONNECTED TO V
IN
(MINUS SWITCH AND L1 VOLTAGE DROP) FOR 2.65V < V
IN
< 3.3V
U
V
IN
= 3.6V
V
IN
= 4.2V
V
IN
= 6V
Burst Mode OPERATION
V
OUT
= 3.3V
L = 6.8µH
1
10
100
OUPUT CURRENT (mA)
1000
1875 TA01a
U
U
1875f
1
LTC1875
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 7V
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 7V
V
SWN
Voltage .............................................. – 0.3V to 7V
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 (Note 3, 6) ........................ 125°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
ORDER PART
NUMBER
LTC1875EGN
GN PART
MARKING
1875
GN PACKAGE
16-LEAD PLASTIC SSOP
T
JMAX
= 125°C,
θ
JA
= 110°C/ W,
θ
JC
= 40°C/ W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
The
q
denotes specifications which apply over the full operating
temperature range, otherwise specifications are T
A
= 25°C. V
IN
= 3.6V 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
Reference Voltage Line Regulation
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
= 3V
V
RUN
= 0V, V
SW
= 0V or 6V, V
IN
= 6V
q
q
q
ELECTRICAL CHARACTERISTICS
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
q
q
q
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
6
UNITS
nA
V
V
mV
mV
%/V
%
%
V
µA
µA
µA
kHz
kHz
kHz
µA
µA
Ω
Ω
A
µA
V
µA
1875f
Undervoltage Trip Limit with Respect to V
FB
∆V
UVL
= V
FB
– V
UVL
2.65
270
15
0
350
495
550
80
10
– 10
0.28
0.35
1.6
0.2
2.15
±0.01
1.0
±0.01
365
22
1
750
605
f
SYNC
f
OSC
I
PLLLPF
3
–3
20
– 20
0.35
0.4
2.75
±2.5
1.5
±1
R
PFET
R
NFET
I
PK
I
LSW
I
SYNC/MODE
V
SYNC/MODE
SYNC/MODE Threshold
2
U
W
U
U
W W
W
LTC1875
ELECTRICAL CHARACTERISTICS
SYMBOL
V
RUN
I
RUN
PARAMETER
RUN Threshold
RUN Input Current
The
q
denotes specifications which apply over the full operating
temperature range, otherwise specifications are T
A
= 25°C. V
IN
= 3.6V unless otherwise noted.
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 LTC1875E is guaranteed to meet specified performance 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 formula:
LTC1875: T
J
= T
A
+ (P
D
• 110°C/W)
Note 4:
The LTC1875 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
0.8
0.7
0.6
R
DS(ON)
(Ω)
0.5
0.4
0.3
0.2
0.1
0
–50
–25
0
25
50
75
TEMPERATURE (°C)
100
125
495
–50
–25
0
25
50
75
TEMPERATURE (°C)
100
125
530
0
2
4
6
SUPPLY VOLTAGE (V)
8
1875 G03
SYNCHRONOUS SWITCH
MAIN SWITCH
V
IN
= 3V
FREQUENCY (kHz)
V
IN
= 5V
555
OSC FREQUENCY (kHz)
1875 G02
V
IN
= 3V
V
IN
= 5V
515
DC Supply Current
vs Temperature
300
V
IN
= 3.6V
250
SUPPLY CURRENT (µA)
PULSE SKIPPING MODE
200
R
DS(ON)
(Ω)
150
100
50
BURST MODE
0
–50
0
0
50
TEMPERATURE (°C)
100
125
0.4
0.3
0.2
0.1
0.5
0.6
SWITCH LEAKAGE (µA)
U W
1875 G01
1875 G04
Oscillator Frequency
vs Temperature
595
V
IN
= 3.6V
580
Oscillator Frequency
vs Supply Voltage
575
570
560
535
550
540
R
DS(ON)
vs Input Voltage
10
9
SYNCHRONOUS SWITCH
8
7
6
5
4
3
2
1
0
2
4
6
INPUT VOLTAGE (V)
8
1875 G05
Switch Leakage Current
vs Temperature
V
IN
= 7V
RUN = 0V
MAIN SWITCH
MAIN SWITCH
SYNCHRONOUS SWITCH
0
–50
0
50
TEMPERATURE (°C)
100
125
1875 G06
1875f
3
LTC1875
TYPICAL PERFOR A CE CHARACTERISTICS
Output Voltage vs Load Current
1.84
1.82
1.80
1.78
1.76
1.74
1.72
1.70
0
500
1000
1500
LOAD CURRENT (mA)
2000
1875 G07
REFERENCE VOLTAGE (mV)
OUTPUT VOLTAGE (V)
Burst Mode OPERATION
V
IN
= 3.6V
L = 4.7µH
Efficiency vs Output Current
95
90
85
EFFICIENCY (%)
100
V
IN
= 3V
V
IN
= 4.2V
V
IN
= 6V
EFFICIENCY (%)
80
75
70
65
60
55
50
0.1
1
10
100
OUTPUT CURRENT (mA)
Efficiency vs Input Voltage
100
95
90
EFFICIENCY (%)
100mA
85
80
75
70
65
60
55
50
2
1mA
I
L
1A/DIV
I
TH
1V/DIV
50µs/DIV
C
IN
= 22µF
C
OUT
= 47µF
I
LOAD
= 200mA to 1700mA
V
OUT
= 2.5V
L = 6.8µH
Burst Mode OPERATION
3
4
5
INPUT VOLTAGE (V)
6
1875 G16
4
U W
Reference Voltage vs
Temperature
805
804
803
802
801
800
799
798
797
796
795
–50
–25
0
25
50
75
TEMPERATURE (°C)
100
125
V
IN
= 6V
1875 G13
Efficiency vs Output Current
90
80
V
IN
= 4.2V
V
IN
= 3.6V
V
IN
= 3.6V
70
60
50
40
30
V
IN
= 3.6V
V
IN
= 4.2V
V
OUT
= 1.8V
L = 4.7µH
Burst Mode OPERATION
1000
1875 G14
20
10
0
0.1
V
OUT
= 1.8V
L = 4.7µH
Burst Mode OPERATION
PULSE SKIPPING MODE
1
10
100
OUTPUT CURRENT (mA)
1000
1875 G15
Load Step (Burst Mode Operation)
V
OUT
100mV/DIV
10mA
0.1mA
1875 G08
V
IN
= 3.6V
V
OUT
= 1.5V
L = 6.8µH
1875f
LTC1875
TYPICAL PERFOR A CE CHARACTERISTICS
Load Step Response (Pulse
Skipping Mode)
V
OUT
100mV/DIV
I
L
1A/DIV
I
TH
1V/DIV
I
L
200mA/DIV
V
IN
= 3.6V
V
OUT
= 1.5V
L = 6.8µH
100µs/DIV
C
IN
= 22µF
C
OUT
= 47µF
I
LOAD
= 200mA to 1700mA
Burst Mode Operation
I
L
200mA/DIV
I
VIN
500mA/DIV
V
OUT
100mV/DIV
RUN/SS
1V/DIV
SW
5V/DIV
5ms/DIV
C
IN
= 22µF
C
OUT
= 47µF
I
LOAD
= 0A
1875 G12
V
IN
= 4.2V
V
OUT
= 2.5V
L = 6.8µH
25µs/DIV
C
IN
= 22µF
C
OUT
= 47µF
I
LOAD
= 50mA
U W
Pulse Skipping Mode Operation
V
OUT
100mV/DIV
SW
5V/DIV
1875 G09
V
IN
= 4.2V
V
OUT
= 2.5V
L = 6.8µH
1µs/DIV
C
IN
= 22µF
C
OUT
= 47µF
I
LOAD
= 50mA
1875 G10
Soft-Start with Shorted Output
1875 G11
V
IN
= 3.6V
V
OUT
= 0V
L = 6.8µH
1875f
5
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