LTC1148
LTC1148-3.3/LTC1148-5
High Efficiency Synchronous
Step-Down Switching Regulators
FEATURES
s
s
DESCRIPTIO
s
s
s
s
s
s
s
s
s
s
Ultrahigh Efficiency: Over 95% Possible
Current-Mode Operation for Excellent Line and Load
Transient Response
High Efficiency Maintained Over Three Decades of
Output Current
Low 160µA Standby Current at Light Loads
Logic Controlled Micropower Shutdown: I
Q
< 20µA
Wide V
IN
Range: 3.5V* to 20V
Short-Circuit Protection
Very Low Dropout Operation: 100% Duty Cycle
Synchronous FET Switching for High Efficiency
Adaptive Nonoverlap Gate Drives
Output Can Be Externally Held High in Shutdown
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.
, 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.
APPLICATI
s
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s
s
S
Notebook and Palmtop Computers
Portable Instruments
Battery-Operated Digital Devices
Cellular Telephones
DC Power Distribution Systems
GPS Systems
TYPICAL APPLICATI
+
1µF
V
IN
P-DRIVE
LTC1148HV-5
SHUTDOWN
SENSE
+
I
TH
SENSE
–
C
T
N-DRIVE
PGND
SGND
V
IN
(5.2V TO 18V)
+
P-CHANNEL
Si4431DY
L*
62µH
C
IN
100µF
95
V
OUT
5V/2A
0V = NORMAL
>1.5V = SHUTDOWN
EFFICIENCY (%)
R
SENSE
**
0.05Ω
1000pF
N-CHANNEL
Si4412DY
D1
MBRS140T3
R
C
1k
C
C
3300pF
+
C
T
470pF
C
OUT
390µF
LT1148 • TA01
*COILTRONICS CTX62-2-MP
**KRL SL-1-C1-0R050J
Figure 1. High Efficiency Step-Down Converter
U
LTC1148-5 Efficiency
100
V
IN
= 6V
V
IN
= 10V
90
85
80
0.02
0.2
LOAD CURRENT (A)
2
LTC1148 • TA01
UO
UO
1
LTC1148
LTC1148-3.3/LTC1148-5
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
ORDER PART
NUMBER
TOP VIEW
P-DRIVE
NC
V
IN
C
T
INTV
CC
I
TH
SENSE
–
1
2
3
4
5
6
7
14 N-DRIVE
13 NC
12 PGND
11 SGND
10 SHUTDOWN
9
8
V
FB
*
SENSE
+
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
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
N PACKAGE
14-LEAD PDIP
S PACKAGE
14-LEAD PLASTIC SO
*FIXED OUTPUT VERSIONS = NC
T
JMAX
= 125°C,
θ
JA
= 70°C/ W (N)
T
JMAX
= 125°C,
θ
JA
= 110°C/ W (S)
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
Consult factory for Industrial and Military grade parts.
ELECTRICAL CHARACTERISTICS
SYMBOL
V
9
I
9
V
OUT
PARAMETER
Feedback Voltage (LTC1148, LTC1148L,
LTC1148HV)
Feedback Current (LTC1148, LTC1148L,
LTC1148HV)
T
A
= 25°C, V
IN
= 10V, V
SHUTDOWN
= 0V unless otherwise noted.
CONDITIONS
V
IN
= 9V
q
q
MIN
1.21
TYP
1.25
0.2
MAX
1.29
1
UNITS
V
µA
Regulated Output Voltage
V
IN
= 9V
LTC1148-3.3, LTC1148HV-3.3, LTC1148L-3.3 I
LOAD
= 700mA
LTC1148-5, LTC1148HV-5
I
LOAD
= 700mA
Output Voltage Line Regulation
V
IN
= 7V to 12V, I
LOAD
= 50mA
Output Voltage Load Regulation
LTC1148-3.3, LTC1148HV-3.3, LTC1148L-3.3 5mA < I
LOAD
< 2A
LTC1148-5, LTC1148HV-5
5mA < I
LOAD
< 2A
Output Ripple (Burst Mode)
I
LOAD
= 0A
q
q
3.23
4.90
– 40
3.33
5.05
0
40
60
50
3.43
5.20
40
65
100
∆V
OUT
q
q
mV
P-P
I
Q
Input DC Supply Current (Note 3)
LTC1148 Series
Normal Mode
Sleep Mode
Sleep Mode (LTC1148-5)
Shutdown
LTC1148HV Series
Normal Mode
Sleep Mode
Sleep Mode (LTC1148HV-5)
Shutdown
LTC1148L Series
Normal Mode
Sleep Mode
Shutdown
(Note 7)
4V < V
IN
< 12V
4V < V
IN
< 12V
6V < V
IN
< 12V
V
SHUTDOWN
= 2.1V, 4V < V
IN
< 12V
4V < V
IN
< 18V
4V < V
IN
< 18V
6V < V
IN
< 18V
V
SHUTDOWN
= 2.1V, 4V < V
IN
< 18V
3.5V < V
IN
< 12V
3.5V < V
IN
< 12V
V
SHUTDOWN
= 2.1V, 3.5V < V
IN
< 12V
1.6
160
160
10
1.6
160
160
10
1.6
160
10
2.1
230
230
20
2.3
250
250
22
2.1
230
20
mA
µA
µA
µA
mA
µA
µA
µA
mA
µA
µA
2
U
V
V
mV
mV
mV
W
U
U
W W
W
LTC1148
LTC1148-3.3/LTC1148-5
ELECTRICAL CHARACTERISTICS
SYMBOL
V
8
– V
7
PARAMETER
Current Sense Threshold Voltage
LTC1148, LTC1148HV, LTC1148L
LTC1148-3.3, LTC1148HV-3.3
LTC1148L-3.3
LTC1148-5, LTC1148HV-5
V
10
I
10
I
4
t
OFF
t
R
, t
F
Shutdown Pin Threshold
Shutdown Pin Input Current
C
T
Pin Discharge Current
Off Time (Note 5)
Driver Output Transition Times
T
A
= 25°C, V
IN
= 10V, V
SHUTDOWN
= 0V, unless otherwise noted.
CONDITIONS
V
SENSE –
= 5V, V
9
= V
OUT
/4 + 25mV (Forced)
V
SENSE –
= 5V, V
9
= V
OUT
/4 – 25mV (Forced)
V
SENSE –
= V
OUT
+ 100mV (Forced)
V
SENSE –
= V
OUT
– 100mV (Forced)
V
SENSE –
= V
OUT
+ 100mV (Forced)
V
SENSE –
= V
OUT
– 100mV (Forced)
0V < V
SHUTDOWN
< 8V, V
IN
= 16V
V
OUT
in Regulation, V
SENSE –
= V
OUT
V
OUT
= 0V
C
T
= 390pF, I
LOAD
= 700mA
C
L
= 3000pF (Pins 1, 14), V
IN
= 6V
50
4
MIN
TYP
25
150
25
150
25
150
0.8
1.2
70
2
5
100
MAX
UNITS
mV
mV
mV
mV
mV
mV
V
µA
µA
µA
µs
ns
q
q
q
130
130
130
0.5
170
170
170
2
5
90
10
6
200
– 40°C
≤
T
A
≤
85°C (Note 5), V
IN
= 10V, unless otherwise noted.
SYMBOL
V
9
∆V
OUT
PARAMETER
Feedback Voltage (LTC1148, LTC1148HV
LTC1148L)
Regulated Output Voltage
LTC1148-3.3, LTC1148HV-3.3, LTC1148L-3.3
LTC1148-5, LTC1148HV-5
Input DC Supply Current (Note 3)
LTC1148 Series
Normal Mode
Sleep Mode
Sleep Mode
Shutdown
LTC1148HV Series
Normal Mode
Sleep Mode
Sleep Mode
Shutdown
LTC1148L Series
Normal Mode
Sleep Mode
Shutdown
Current Sense Threshold Voltage
LTC1148, LTC1148HV, LTC1148L (Note 4)
CONDITIONS
V
IN
= 9V
V
IN
= 9V
I
LOAD
= 700mA
I
LOAD
= 700mA
(Note 7)
4V < V
IN
< 12V
4V < V
IN
< 12V
6V < V
IN
< 12V
V
SHUTDOWN
= 2.1V, 4V < V
IN
< 12V
4V < V
IN
< 18V
4V < V
IN
< 18V
6V < V
IN
< 18V
V
SHUTDOWN
= 2.1V, 4V < V
IN
< 18V
3.5V < V
IN
< 12V
3.5V < V
IN
< 12V
V
SHUTDOWN
= 2.1V, 3.5V < V
IN
< 12V
V
SENSE –
= 5V, V
9
= V
OUT
/4 – 25mV (Forced)
V
SENSE –
= 5V, V
9
= V
OUT
/4 + 25mV (Forced)
1.6
160
160
10
1.6
160
160
10
1.6
160
10
25
150
25
150
25
150
0.8
5
2.4
260
260
22
2.6
280
280
24
2.4
260
22
mA
µA
µA
µA
mA
µA
µA
µA
mA
µA
µA
mV
mV
mV
mV
mV
mV
V
µs
MIN
1.20
TYP
1.25
MAX
1.30
UNITS
V
3.17
4.85
3.33
5.05
3.43
5.20
V
V
I
Q
V
8
– V
7
125
125
125
0.55
3.8
175
175
175
2
6
LTC1148-3.3, LTC1148HV-3.3, LTC1148L-3.3 V
SENSE –
= V
OUT
+ 100mV (Forced)
V
SENSE –
= V
OUT
– 100mV (Forced)
LTC1148-5, LTC1148HV-5
V
10
t
OFF
Shutdown Pin Threshold
Off Time (Note 5)
C
T
= 390pF, I
LOAD
= 700mA
V
SENSE –
= V
OUT
+ 100mV (Forced)
V
SENSE –
= V
OUT
– 100mV (Forced)
3
LTC1148
LTC1148-3.3/LTC1148-5
ELECTRICAL CHARACTERISTICS
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.
Note 7:
The LTC1148L and LTC1148L-3.3 allow operation to V
IN
= 3.5V.
TYPICAL PERFOR A CE CHARACTERISTICS
Efficiency vs Input Voltage
100
98
96
EFFICIENCY (%)
FIGURE 1 CIRCUIT
94
92
90
88
86
84
82
80
0
4
I
LOAD
= 1A
∆V
OUT
(mV)
∆V
OUT
(mV)
I
LOAD
= 100mA
12
8
INPUT VOLTAGE (V)
LTC1148 • TPC01
DC Supply Current
2.1
1.8
NOT INCLUDING
GATE CHARGE CURRENT
SUPPLY CURRENT (µA)
NORMALIZED FREQUENCY
SUPPLY CURRENT (mA)
1.5
1.2
0.9
0.6
0.3
0
0
2
4
6
ACTIVE MODE
SLEEP MODE
8 10 12 14 16 18 20
INPUT VOLTAGE
LTC1148 • TPC04
4
U W
16
20
Line Regulation
40
30
20
10
0
–10
–20
–30
–40
0
4
8
12
16
20
INPUT VOLTAGE (V)
LTC1148 • TPC02
Load Regulation
20
FIGURE 1 CIRCUIT
R
SENSE
= 0.05Ω
FIGURE 1 CIRCUIT
I
LOAD
= 1A
0
–20
–40
–60
–80
–100
0
0.5
V
IN
= 12V
V
IN
= 6V
1
1.5
LOAD CURRENT (A)
2
2.5
LTC1148 • TPC03
Supply Current in Shutdown
20
18
16
14
12
10
8
6
4
2
0
0
2
4
6 8 10 12 14 16 18 20
INPUT VOLTAGE (V)
LTC1148 • TPC05
Operating Frequency
vs (V
IN
– V
OUT
)
1.6
V
OUT
= 5V
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
0
2
4
8
10
6
(V
IN
– V
OUT
) VOLTAGE (V)
12
70°C
25°C
0°C
V
SHUTDOWN
= 2V
LTC1148 • TPC06
LTC1148
LTC1148-3.3/LTC1148-5
TYPICAL PERFOR A CE CHARACTERISTICS
Gate Charge Supply Current
28
24
20
16
12
8
4
0
20
260
80
200
140
OPERATING FREQUENCY (kHz)
LTC1148 • TPC07
GATE CHARGE CURRENT (mA)
SENSE VOLTAGE (mV)
OFF TIME (µs)
Q
N
+ Q
P
= 100nC
Q
N
+ Q
P
= 50nC
PI FU CTIO S
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
< 1µs, 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
.
U W
Off Time vs V
OUT
80
70
60
50
40
30
20
10
LTC1148-3.3
0
0
1
2
3
4
5
LTC1148-5
V
SENSE –
= V
OUT
Current Sense Threshold Voltage
175
150
125
100
75
50
25
0
0
20
60
40
TEMPERATURE (°C)
80
100
MAXIMUM
THRESHOLD
MINIMUM
THRESHOLD
OUTPUT VOLTAGE (V)
LTC1148 • TPC08
LTC1148 • TPC09
U
U
U
5
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