1
LTC1148
LTC1148-3.3/LTC1148-5
High Efficiency Synchronous
Step-Down Switching Regulators
LOAD CURRENT (A)
0.02
80
EFFICIENCY (%)
85
90
100
0.2
2
LTC1148 TA01
95
V
IN
= 6V
V
IN
= 10V
LTC1148-5 Efficiency
S
FEATURE
D
U
ESCRIPTIO
s
Ultrahigh Efficiency: Over 95% Possible
s
Current-Mode Operation for Excellent Line and Load
Transient Response
s
High Efficiency Maintained Over Three Decades of
Output Current
s
Low 160
A Standby Current at Light Loads
s
Logic Controlled Micropower Shutdown: I
Q
< 20
A
s
Wide V
IN
Range: 3.5V* to 20V
s
Short-Circuit Protection
s
Very Low Dropout Operation: 100% Duty Cycle
s
Synchronous FET Switching for High Efficiency
s
Adaptive Nonoverlap Gate Drives
s
Output Can Be Externally Held High in Shutdown
s
Available in 14-Pin Narrow SO Package
The LTC
1148 series is a family of synchronous step-
down switching regulator controllers featuring automatic
Burst Mode
TM
operation to maintain high efficiencies at
low output currents. These devices drive external comple-
mentary power MOSFETs at switching frequencies up to
250kHz using a constant off-time current-mode architec-
ture providing constant ripple current in the inductor.
The operating current level is user-programmable via an
external current sense resistor. Wide input supply range
allows operation from 3.5V* to 18V (20V maximum).
Constant off-time architecture provides low dropout regu-
lation limited by only the R
DS(ON)
of the external MOSFET
and resistance of the inductor and current sense resistor.
The LTC1148 series combines synchronous switching for
maximum efficiency at high currents with an automatic low
current operating mode, called Burst Mode
operation, which
reduces switching losses. Standby power is reduced to only
2mW at V
IN
= 10V (at I
OUT
= 0). Load currents in Burst Mode
operation are typically 0mA to 300mA.
For operation up to 48V input, see the LTC1149 and
LTC1159 data sheets and Application Note 54.
Figure 1. High Efficiency Step-Down Converter
U
A
O
PPLICATI
TYPICAL
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode
is a trademark of Linear Technology Corporation.
* LTC1148L and LTC1148L-3.3 only.
U
S
A
O
PPLICATI
s
Notebook and Palmtop Computers
s
Portable Instruments
s
Battery-Operated Digital Devices
s
Cellular Telephones
s
DC Power Distribution Systems
s
GPS Systems
0V = NORMAL
>1.5V = SHUTDOWN
P-CHANNEL
Si4431DY
+
1
F
L*
62
H
R
SENSE
**
0.05
V
OUT
5V/2A
+
C
IN
100
F
V
IN
(5.2V TO 18V)
I
TH
C
T
SGND
C
T
470pF
C
C
3300pF
R
C
1k
+
C
OUT
390
F
D1
MBRS140T3
LT1148 TA01
N-DRIVE
PGND
N-CHANNEL
Si4412DY
V
IN
P-DRIVE
LTC1148HV-5
SHUTDOWN
SENSE
+
SENSE
1000pF
COILTRONICS CTX62-2-MP
KRL SL-1-C1-0R050J
*
**
2
LTC1148
LTC1148-3.3/LTC1148-5
A
U
G
W
A
W
U
W
A
R
BSOLUTE
XI
TI
S
ORDER PART
NUMBER
LTC1148CN
LTC1148HVCN
LTC1148CN-3.3
LTC1148HVCN-3.3
LTC1148CN-5
LTC1148HVCN-5
LTC1148CS
LTC1148HVCS
LTC1148LCS
LTC1148CS-3.3
LTC1148HVCS-3.3
LTC1148LCS-3.3
LTC1148CS-5
LTC1148HVCS-5
LTC1148HVIS-5
W
U
U
PACKAGE/ORDER I FOR ATIO
Consult factory for Military grade parts.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
V
9
Feedback Voltage (LTC1148, LTC1148L,
V
IN
= 9V
q
1.21
1.25
1.29
V
LTC1148HV)
I
9
Feedback Current (LTC1148, LTC1148L,
q
0.2
1
A
LTC1148HV)
V
OUT
Regulated Output Voltage
V
IN
= 9V
LTC1148-3.3, LTC1148HV-3.3, LTC1148L-3.3 I
LOAD
= 700mA
q
3.23
3.33
3.43
V
LTC1148-5, LTC1148HV-5
I
LOAD
= 700mA
q
4.90
5.05
5.20
V
V
OUT
Output Voltage Line Regulation
V
IN
= 7V to 12V, I
LOAD
= 50mA
40
0
40
mV
Output Voltage Load Regulation
LTC1148-3.3, LTC1148HV-3.3, LTC1148L-3.3 5mA < I
LOAD
< 2A
q
40
65
mV
LTC1148-5, LTC1148HV-5
5mA < I
LOAD
< 2A
q
60
100
mV
Output Ripple (Burst Mode)
I
LOAD
= 0A
50
mV
P-P
I
Q
Input DC Supply Current (Note 3)
(Note 7)
LTC1148 Series
Normal Mode
4V < V
IN
< 12V
1.6
2.1
mA
Sleep Mode
4V < V
IN
< 12V
160
230
A
Sleep Mode (LTC1148-5)
6V < V
IN
< 12V
160
230
A
Shutdown
V
SHUTDOWN
= 2.1V, 4V < V
IN
< 12V
10
20
A
LTC1148HV Series
Normal Mode
4V < V
IN
< 18V
1.6
2.3
mA
Sleep Mode
4V < V
IN
< 18V
160
250
A
Sleep Mode (LTC1148HV-5)
6V < V
IN
< 18V
160
250
A
Shutdown
V
SHUTDOWN
= 2.1V, 4V < V
IN
< 18V
10
22
A
LTC1148L Series
Normal Mode
3.5V < V
IN
< 12V
1.6
2.1
mA
Sleep Mode
3.5V < V
IN
< 12V
160
230
A
Shutdown
V
SHUTDOWN
= 2.1V, 3.5V < V
IN
< 12V
10
20
A
T
A
= 25
C, V
IN
= 10V, V
SHUTDOWN
= 0V unless otherwise noted.
ELECTRICAL C
C
HARA TERISTICS
1
2
3
4
5
6
7
TOP VIEW
S PACKAGE
14-LEAD PLASTIC SO
N PACKAGE
14-LEAD PDIP
14
13
12
11
10
9
8
P-DRIVE
NC
V
IN
C
T
INTV
CC
I
TH
SENSE
N-DRIVE
NC
PGND
SGND
SHUTDOWN
V
FB
*
SENSE
+
*FIXED OUTPUT VERSIONS = NC
T
JMAX
= 125
C,
JA
= 70
C/ W (N)
T
JMAX
= 125
C,
JA
= 110
C/ W (S)
(Note 1)
Input Supply Voltage (Pin 3)
LTC1148 and LTC1148L Series ............ 16V to 0.3V
LTC1148HV Series ............................... 20V to 0.3V
Continuous Output Current (Pins 1, 14) .............. 50mA
Sense Voltages (Pins 7, 8)
LTC1148HV (Adjustable Only)
V
IN
12.7V ...................................... 13V to 0.3V
V
IN
< 12.7V ......................... (V
IN
+ 0.3V) to 0.3V
Operating Ambient Temperature Range ...... 0
C to 70
C
Extended Commercial and Industrial
Temperature Range ............................... 40
C to 85
C
Junction Temperature (Note 2) ............................ 125
C
Storage Temperature Range ................ 65
C to 150
C
Lead Temperature (Soldering, 10 sec)................. 300
C
3
LTC1148
LTC1148-3.3/LTC1148-5
T
A
= 25
C, V
IN
= 10V, V
SHUTDOWN
= 0V, unless otherwise noted.
ELECTRICAL C
C
HARA TERISTICS
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
V
8
V
7
Current Sense Threshold Voltage
LTC1148, LTC1148HV, LTC1148L
V
SENSE
= 5V, V
9
= V
OUT
/4 + 25mV (Forced)
25
mV
V
SENSE
= 5V, V
9
= V
OUT
/4 25mV (Forced)
q
130
150
170
mV
LTC1148-3.3, LTC1148HV-3.3
V
SENSE
= V
OUT
+ 100mV (Forced)
25
mV
LTC1148L-3.3
V
SENSE
= V
OUT
100mV (Forced)
q
130
150
170
mV
LTC1148-5, LTC1148HV-5
V
SENSE
= V
OUT
+ 100mV (Forced)
25
mV
V
SENSE
= V
OUT
100mV (Forced)
q
130
150
170
mV
V
10
Shutdown Pin Threshold
0.5
0.8
2
V
I
10
Shutdown Pin Input Current
0V < V
SHUTDOWN
< 8V, V
IN
= 16V
1.2
5
A
I
4
C
T
Pin Discharge Current
V
OUT
in Regulation, V
SENSE
= V
OUT
50
70
90
A
V
OUT
= 0V
2
10
A
t
OFF
Off Time (Note 5)
C
T
= 390pF, I
LOAD
= 700mA
4
5
6
s
t
R
, t
F
Driver Output Transition Times
C
L
= 3000pF (Pins 1, 14), V
IN
= 6V
100
200
ns
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
V
9
Feedback Voltage (LTC1148, LTC1148HV
V
IN
= 9V
1.20
1.25
1.30
V
LTC1148L)
V
OUT
Regulated Output Voltage
V
IN
= 9V
LTC1148-3.3, LTC1148HV-3.3, LTC1148L-3.3
I
LOAD
= 700mA
3.17
3.33
3.43
V
LTC1148-5, LTC1148HV-5
I
LOAD
= 700mA
4.85
5.05
5.20
V
I
Q
Input DC Supply Current (Note 3)
(Note 7)
LTC1148 Series
Normal Mode
4V < V
IN
< 12V
1.6
2.4
mA
Sleep Mode
4V < V
IN
< 12V
160
260
A
Sleep Mode
6V < V
IN
< 12V
160
260
A
Shutdown
V
SHUTDOWN
= 2.1V, 4V < V
IN
< 12V
10
22
A
LTC1148HV Series
Normal Mode
4V < V
IN
< 18V
1.6
2.6
mA
Sleep Mode
4V < V
IN
< 18V
160
280
A
Sleep Mode
6V < V
IN
< 18V
160
280
A
Shutdown
V
SHUTDOWN
= 2.1V, 4V < V
IN
< 18V
10
24
A
LTC1148L Series
Normal Mode
3.5V < V
IN
< 12V
1.6
2.4
mA
Sleep Mode
3.5V < V
IN
< 12V
160
260
A
Shutdown
V
SHUTDOWN
= 2.1V, 3.5V < V
IN
< 12V
10
22
A
V
8
V
7
Current Sense Threshold Voltage
LTC1148, LTC1148HV, LTC1148L (Note 4)
V
SENSE
= 5V, V
9
= V
OUT
/4 25mV (Forced)
25
mV
V
SENSE
= 5V, V
9
= V
OUT
/4 + 25mV (Forced)
125
150
175
mV
LTC1148-3.3, LTC1148HV-3.3, LTC1148L-3.3 V
SENSE
= V
OUT
+ 100mV (Forced)
25
mV
V
SENSE
= V
OUT
100mV (Forced)
125
150
175
mV
LTC1148-5, LTC1148HV-5
V
SENSE
= V
OUT
+ 100mV (Forced)
25
mV
V
SENSE
= V
OUT
100mV (Forced)
125
150
175
mV
V
10
Shutdown Pin Threshold
0.55
0.8
2
V
t
OFF
Off Time (Note 5)
C
T
= 390pF, I
LOAD
= 700mA
3.8
5
6
s
40
C
T
A
85
C (Note 5), V
IN
= 10V, unless otherwise noted.
4
LTC1148
LTC1148-3.3/LTC1148-5
ELECTRICAL C
C
HARA TERISTICS
The
q
denotes specifications which apply over the full operating
temperature range.
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: T
J
is calculated from the ambient temperature T
A
and power
dissipation P
D
according to the following formulas:
LTC1148CN, LTC1148CN-3.3, LTC1148CN-5: T
J
= T
A
+ (P
D
70
C/W)
LTC1148CS, LTC1148CS-3.3, LTC1148CS-5: T
J
= T
A
+ (P
D
110
C/W)
Note 3: Dynamic supply current is higher due to the gate charge being
delivered at the switching frequency. See Applications Information.
Note 4: The LTC1148 and LTC1148HV versions are tested with external
feedback resistors resulting in a nominal output voltage of 5V. The
LTC1148L version is tested with external feedback resistors resulting in a
nominal output voltage of 2.5V.
Note 5: In applications where R
SENSE
is placed at ground potential, the off
time increases approximately 40%.
Note 6: The LTC1148, LTC1148HV and LTC1148L series are not tested
and not quality assurance sampled at 40
C and 85
C. These
specifications are guaranteed by design and/or correlation. The
LTC1148HVI-5 is guaranteed over the full 40
C to 85
C operating
temperature range.
Note 7: The LTC1148L and LTC1148L-3.3 allow operation to V
IN
= 3.5V.
C
C
HARA TERISTICS
U
W
A
TYPICAL PERFOR
CE
Line Regulation
Efficiency vs Input Voltage
LOAD CURRENT (A)
0
100
V
OUT
(mV)
80
60
40
20
0
20
0.5
1
1.5
2
LTC1148 TPC03
2.5
FIGURE 1 CIRCUIT
R
SENSE
= 0.05
V
IN
= 6V
V
IN
= 12V
INPUT VOLTAGE (V)
0
80
EFFICIENCY (%)
82
86
88
90
100
94
4
8
LTC1148 TPC01
84
96
98
92
12
16
20
I
LOAD
= 100mA
FIGURE 1 CIRCUIT
I
LOAD
= 1A
DC Supply Current
Supply Current in Shutdown
Load Regulation
Operating Frequency
vs (V
IN
V
OUT
)
(V
IN
V
OUT
) VOLTAGE (V)
0
NORMALIZED FREQUENCY
0.6
1.0
8
LTC1148 TPC06
0.4
0
2
4
6
0.2
1.2
0.8
10
12
1.4
1.6
V
OUT
= 5V
0C
70C
25C
INPUT VOLTAGE
0
0
SUPPLY CURRENT (mA)
0.3
0.9
1.2
1.5
4
LTC1148 TPC04
0.6
2
6
1.8
2.1
8
10 12 14 16 18
SLEEP MODE
ACTIVE MODE
NOT INCLUDING
GATE CHARGE CURRENT
20
INPUT VOLTAGE (V)
0
0
SUPPLY CURRENT (
A)
2
6
8
10
20
14
4
8
10
18
LTC1148 TPC05
4
16
18
12
2
6
12
14 16
V
SHUTDOWN
= 2V
20
INPUT VOLTAGE (V)
0
V
OUT
(mV)
0
10
20
16
LTC1148 TPC02
10
20
40
4
8
12
30
40
30
FIGURE 1 CIRCUIT
I
LOAD
= 1A
20
5
LTC1148
LTC1148-3.3/LTC1148-5
C
C
HARA TERISTICS
U
W
A
TYPICAL PERFOR
CE
Current Sense Threshold Voltage
TEMPERATURE (C)
0
0
SENSE VOLTAGE (mV)
25
50
75
175
125
20
40
150
100
60
80
100
MAXIMUM
THRESHOLD
MINIMUM
THRESHOLD
LTC1148 TPC09
Off Time vs V
OUT
OUTPUT VOLTAGE (V)
0
OFF TIME (
s)
40
50
60
4
LTC1148 TPC08
30
20
0
1
2
3
10
80
70
5
LTC1148-5
LTC1148-3.3
V
SENSE
= V
OUT
Gate Charge Supply Current
OPERATING FREQUENCY (kHz)
20
0
GATE CHARGE CURRENT (mA)
4
8
12
28
20
80
140
24
16
200
260
Q
N
+ Q
P
= 100nC
Q
N
+ Q
P
= 50nC
LTC1148 TPC07
P-DRIVE (Pin 1): High Current Drive for Top P-Channel
MOSFET. Voltage swing at this pin is from V
IN
to ground.
NC (Pin 2): No Connection. Can connect to power ground.
V
IN
(Pin 3): Main Supply Pin. Must be closely decoupled
to power ground Pin 12.
C
T
(Pin 4): External capacitor C
T
from Pin 4 to ground sets
the operating frequency. The actual frequency is also
dependent upon the input voltage.
INTV
CC
(Pin 5): Internal Supply Voltage, Nominally 3.3V.
Can be decoupled to signal ground. Do not externally load
this pin.
I
TH
(Pin 6): Gain Amplifier Decoupling Point. The current
comparator threshold increases with the Pin 6 voltage.
SENSE
(Pin 7): Connects to internal resistive divider
which sets the output voltage in LTC1148-3.3 and
LTC1148-5 versions. Pin 7 is also the () input for the
current comparator.
SENSE
+
(Pin 8): The (+) Input to the Current Comparator.
A built-in offset between Pins 7 and 8 in conjunction with
R
SENSE
sets the current trip threshold.
V
FB
(Pin 9): For the LTC1148 adjustable version, Pin 9
serves as the feedback pin from an external resistive
divider used to set the output voltage. On LTC1148-3.3
and LTC1148-5 versions this pin is not used.
SHUTDOWN (Pin 10): When grounded, the LTC1148
series operates normally. Pulling Pin 10 high holds both
MOSFETs off and puts the LTC1148 series in micropower
shutdown mode. Requires CMOS logic signal with t
R
,
t
F
< 1
s, should not be left floating.
SGND (Pin 11): Small-Signal Ground. Must be routed
separately from other grounds to the () terminal of C
OUT
.
PGND (Pin 12): Driver Power Ground. Connects to source
of N-channel MOSFET and the () terminal of C
IN
.
NC (Pin 13): No Connection. Can connect to power ground.
N-DRIVE (Pin 14): High Current Drive for Bottom
N-Channel MOSFET. Voltage swing at Pin 14 is from
ground to V
IN
.
PI FU CTIO S
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