LTC1147-3.3
LTC1147-5/LTC1147L
High Efficiency Step-Down
Switching Regulator Controllers
FEATURES
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DESCRIPTIO
s
s
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Very High Efficiency: Over 95% Possible
Wide V
IN
Range: 3.5V* to 16V
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
Short-Circuit Protection
Very Low Dropout Operation: 100% Duty Cycle
High Efficiency in a Small Amount of Board Space
Output Can Be Externally Held High in Shutdown
Available in 8-Pin SO Package
The LTC
®
1147 series are step-down switching regulator
controllers featuring automatic Burst Mode
TM
operation to
maintain high efficiencies at low output currents. These
devices drive an external P-channel power MOSFET at
switching frequencies exceeding 400kHz using a constant
off-time current mode architecture 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 14V (16V 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 LTC1147 series incorporates automatic power saving
Burst Mode operation to reduce switching losses when
load currents drop below the level required for continuous
operation. 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 applications where even higher efficiency is required,
refer to the LTC1148 data sheet and Application Note 54.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a trademark of Linear Technology Corporation.
*LTC1147L and LTC1147L-3.3 only.
APPLICATIO S
s
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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
V
IN
(5.2V TO 14V)
+
PDRIVE
LTC1147-5
SHDN
SENSE
+
I
TH
SENSE
–
C
T
GND
P-CHANNEL
Si4431DY
L*
50µH
100
C
IN
100µF
R
SENSE
**
0.05Ω
0V = NORMAL
>1.5V = SHUTDOWN
V
OUT
5V/2A
EFFICIENCY (%)
1000pF
R
C
1k
C
C
3300pF
+
D1
MBRD330
C
T
470pF
C
OUT
390µF
LT1147 • F01
*COILTRONICS CTX50-2-MP
**KRL SL-1-C1-0R050J
Figure 1. High Efficiency Step-Down Converter
U
LTC1147-5 Efficiency
95
90
V
IN
= 10V
85
80
75
70
0.001
V
IN
= 6V
0.01
0.1
1
LT1147 • TA01
UO
U
LOAD CURRENT (A)
1
LTC1147-3.3
LTC1147-5/LTC1147L
ABSOLUTE
AXI U RATI GS
Operating Ambient Temperature Range
LTC1147C................................................ 0°C to 70°C
LTC1147I............................................. –40°C to 85°C
Extended Commercial
Temperature Range (Note 4) ................. – 40°C to 85°C
Junction Temperature (Note 1)............................ 125°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
Input Supply Voltage (Pin 1)..................... 16V to – 0.3V
Continuous Output Current (Pin 8) ...................... 50mA
Sense Voltages (Pins 4, 5)
V
IN
≥
12.7V ...........................................13V to – 0.3V
V
IN
< 12.7V ............................... (V
IN
+ 0.3V) to – 0.3V
PACKAGE/ORDER I FOR ATIO
TOP VIEW
V
IN
1
C
T
2
I
TH
3
SENSE
–
8
7
6
5
PDRIVE
GND
SHDN
(V
FB
*)
SENSE
+
4
N8 PACKAGE
S8 PACKAGE
8-LEAD PLASTIC DIP 8-LEAD PLASTIC SO
* ADJUSTABLE OUTPUT VERSION
LTC1147CN8-3.3
LTC1147CN8-5
LTC1147CS8-3.3
LTC1147CS8-5
LTC1147IS8-3.3
T
JMAX
= 125°C,
θ
JA
= 110°C/W (N)
T
JMAX
= 125°C,
θ
JA
= 150°C/W (S)
Consult factory for Military grade parts.
ELECTRICAL CHARACTERISTICS
SYMBOL
V
6
I
6
V
OUT
PARAMETER
Feedback Voltage (LTC1147L)
Feedback Current (LTC1147L)
Regulated Output Voltage
LTC1147-3.3, LTC1147L-3.3
LTC1147-5
Output Voltage Line Regulation
Output Voltage Load Regulation
LTC1147-3.3, LTC1147L-3.3
LTC1147-5
Burst Mode Output Ripple
I
Q
Input DC Supply Current (Note 2)
LTC1147 Series
Normal Mode
Sleep Mode
Sleep Mode (LTC1147-5)
Shutdown
LTC1147L Series
Normal Mode
Sleep Mode
Shutdown (LTC1147L-3.3)
T
A
= 25°C, V
IN
= 10V, V
SHDN
= 0V, unless otherwise noted.
MIN
q
q
CONDITIONS
V
IN
= 9V
V
IN
= 9V
I
LOAD
= 700mA
I
LOAD
= 700mA
V
IN
= 7V to 12V, I
LOAD
= 50mA
5mA < I
LOAD
< 2A
5mA < I
LOAD
< 2A
I
LOAD
= 0A
(Note 5)
4V < V
IN
< 12V
4V < V
IN
< 12V
5V < V
IN
< 12V
V
SHDN
= 2.1V, 4V < V
IN
< 12V
3.5V < V
IN
< 12V
3.5V < V
IN
< 12V
V
SHDN
= 2.1V, 3.5V < V
IN
< 12V
q
q
∆V
OUT
2
U
U
W
W W
U
W
ORDER PART NUMBER
LTC1147LCS8
LTC1147LCS8-3.3
LTC1147LIS8
S8 PART MARKING
11473
11475
1147L
1147L3
1147LI
1147I3
TYP
1.25
0.2
MAX
1.29
1
3.43
5.20
40
65
100
UNITS
V
µA
V
V
mV
mV
mV
mV
P-P
1.21
q
q
3.23
4.90
– 40
3.33
5.05
0
40
60
50
1.6
160
160
10
1.6
160
10
2.1
230
230
20
2.1
230
20
mA
µA
µA
µA
mA
µA
µA
LTC1147-3.3
LTC1147-5/LTC1147L
ELECTRICAL CHARACTERISTICS
SYMBOL
V
5
– V
4
PARAMETER
Current Sense Threshold Voltage (Note 6)
LTC1147-3.3, LTC1147L-3.3
LTC1147–5
LTC1147L
V
6
I
6
I
2
t
OFF
t
r
, t
f
SHDN Pin Threshold
LTC1147-3.3/LTC1147-5/LTC1147L-3.3
SHDN Pin Input Current
LTC1147-3.3/LTC1147-5/LTC1147L-3.3
C
T
Pin Discharge Current
Off-Time (Note 3)
Driver Output Transition Times
T
A
= 25°C, V
IN
= 10V, V
SHDN
= 0V, unless otherwise noted.
MIN
TYP
25
150
25
150
25
150
0.8
1.2
50
4
70
2
5
100
MAX
UNITS
mV
mV
mV
mV
mV
mV
V
µA
µA
µA
µs
ns
CONDITIONS
V
SENSE–
= V
OUT
+ 100mV (Forced)
V
SENSE–
= V
OUT
– 100mV (Forced)
V
SENSE–
= V
OUT
+ 100mV (Forced)
V
SENSE–
= V
OUT
– 100mV (Forced)
V
SENSE–
= 5V, V6 = V
OUT
/4 + 25mV (Forced)
V
SENSE–
= 5V, V6 = V
OUT
/4 – 25mV (Forced)
130
130
130
0.5
170
170
170
2
5
90
10
6
200
0V < V
SHDN
< 8V, V
IN
= 16V
V
OUT
in Regulation, V
SENSE –
= V
OUT
V
OUT
= 0V
C
T
= 390pF, I
LOAD
= 700mA
C
L
= 3000pF (Pin 8), V
IN
= 6V
– 40°C
≤
T
A
≤
85°C (Note 4), V
IN
= 10V, unless otherwise noted.
SYMBOL
V
6
V
OUT
PARAMETER
Feedback Voltage (LTC1147L)
Regulated Output Voltage
LTC1147-3.3/LTC1147L-3.3
LTC1147-5
Input DC Supply Current (Note 2)
LTC1147 Series
Normal Mode
Sleep Mode
Sleep Mode (LTC1147-5)
Shutdown
LTC1147L Series
Normal Mode
Sleep Mode
Shutdown (LTC1147L-3.3)
Current Sense Threshold Voltage (Note 6)
LTC1147-3.3
LTC1147-5
LTC1147L
V
6
t
OFF
SHDN Pin Threshold
LTC1147-3.3/LTC1147-5/LTC1147L-3.3
Off-Time (Note 3)
CONDITIONS
V
IN
= 9V
V
IN
= 9V
I
LOAD
= 700mA
I
LOAD
= 700mA
(Note 5)
4V < V
IN
< 12V
4V < V
IN
< 12V
5V < V
IN
< 12V
V
SHDN
= 2.1V, 4V < V
IN
< 12V
3.5V < V
IN
< 12V
3.5V < V
IN
< 12V
V
SHDN
= 2.1V, 3.5V < V
IN
< 12V
V
SENSE –
= V
OUT
+ 100mV (Forced)
V
SENSE –
= V
OUT
– 100mV (Forced)
V
SENSE –
= V
OUT
+ 100mV (Forced)
V
SENSE –
= V
OUT
– 100mV (Forced)
V
SENSE–
= 5V, 6V = V
OUT
/4 + 25mV (Forced)
V
SENSE–
= 5V, 6V = V
OUT
/4 – 25mV (Forced)
0V < V
SHDN
< 8V, V
IN
= 16V
C
T
= 390pF, I
LOAD
= 700mA
1.6
160
160
10
1.6
160
10
25
150
25
150
25
150
0.8
5
2.4
260
260
22
2.4
260
22
mA
µA
µA
µA
mA
µA
µA
mV
mV
mV
mV
mV
mV
V
µs
q
q
q
MIN
1.20
3.17
4.85
TYP
1.25
3.33
5.05
MAX
1.30
3.43
5.20
UNITS
V
V
V
I
Q
V
5
– V
4
q
q
125
125
125
0.5
3.8
185
185
185
2
6.5
The
q
denotes specifications which apply over the full specified
temperature range.
Note 1:
T
J
is calculated from the ambient temperature T
A
and power
dissipation P
D
according to the following formulas:
LTC1147CN8-3.3/LTC1147CN8-5: T
J
= T
A
+ (P
D
)(110°C/W)
LTC1147LIS/LTC1147IS8/LTC1147LCS/
LTC1147CS8-3.3/LTC1147CS8-5: T
J
= T
A
+ (P
D
)(150°C/W)
Note 2:
Dynamic supply current is higher due to the gate charge being
delivered at the switching frequency. See Applications Information.
Note 3:
In applications where R
SENSE
is placed at ground potential, the off-
time increases approximately 40%.
Note 4:
The LTC1147C is guaranteed to meet specified performance from
0°C to 70°C and is designed, characterized and expected to meet these
extended temperature limits, but is not tested at – 40°C and 85°C. The
LTC1147I is guaranteed to meet the extended temperature limits.
Note 5:
The LTC1147L/LTC1147L-3.3 allow operation to V
IN
= 3.5V.
Note 6:
The LTC1147L is tested with external feedback resistors resulting
in a nominal output voltage of 2.5V.
3
LTC1147-3.3
LTC1147-5/LTC1147L
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
∆V
OUT
(mV)
∆V
OUT
(mV)
I
LOAD
= 1A
I
LOAD
= 100mA
12
8
INPUT VOLTAGE (V)
DC Supply Current
2.1
1.8
SUPPLY CURRENT (mA)
NOT INCLUDING
GATE CHARGE CURRENT
SUPPLY CURRENT (µA)
NORMALIZED FREQUENCY
1.5
1.2
0.9
0.6
0.3
0
0
2
4
ACTIVE MODE
SLEEP MODE
8 10 12 14
6
INPUT VOLTAGE (V)
16
18
Gate Charge Supply Current
14
12
10
OFF-TIME (µs)
GATE CHARGE CURRENT (mA)
SENSE VOLTAGE (mV)
8
6
4
Q
P
= 50nC
Q
P
= 29nC
2
0
20
260
80
200
140
OPERATING FREQUENCY (kHz)
LTC1147 • G07
4
U W
16
LTC1147 • G01
Line Regulation
40
30
20
10
0
–10
–20
–30
–40
0
4
8
12
16
LTC1147 • G02
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
INPUT VOLTAGE (V)
1.0
1.5
LOAD CURRENT (A)
2.0
2.5
LTC1147 • G03
Supply Current in Shutdown
20
18
16
14
12
10
8
6
4
2
0
0
2
4
6
8 10 12 14
INPUT VOLTAGE (V)
16
18
V
SHUTDOWN
= 2V
(NOT AVAILABLE ON LTC1147L)
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
8
10
6
(V
IN
– V
OUT
) VOLTAGE (V)
4
12
70°C
25°C
0°C
LTC1147 • G04
LTC1147 • G05
LTC1148 • G06
Off-Time vs V
OUT
80
70
60
50
40
30
20
10
LTC1147-3.3
0
0
1
2
3
4
5
LTC1147-5
V
SENSE –
= V
OUT
175
150
125
100
75
50
25
0
Current Sense Threshold Voltage
MAXIMUM
THRESHOLD
MINIMUM
THRESHOLD
0
20
OUTPUT VOLTAGE (V)
LTC1147 • G08
60
40
TEMPERATURE (°C)
80
100
LTC1147 • G09
LTC1147-3.3
LTC1147-5/LTC1147L
PI FU CTIO S
V
IN
(Pin 1):
Main Supply Pin. Must be closely decoupled
to ground Pin 7.
C
T
(Pin 2):
External capacitor C
T
from Pin 2 to ground sets
the operating frequency. The actual frequency is also
dependent upon the input voltage.
I
TH
(Pin 3):
Gain Amplifier Decoupling Point. The current
comparator threshold increases with the Pin 3 voltage.
SENSE
–
(Pin 4):
Connects to internal resistive divider
which sets the output voltage. Pin 4 is also the (–) input for
the current comparator.
SENSE
+
(Pin 5):
The (+) input to the current comparator.
A built-in offset between Pins 4 and 5 in conjunction with
R
SENSE
sets the current trip threshold.
SHDN/V
FB
(Pin 6):
When grounded, the fixed output
versions of the LTC1147 family operate normally. Pulling
Pin 6 high holds the P-channel MOSFET off and puts the
LTC1147 in micropower shutdown mode. Requires CMOS
logic signal with t
r
, t
f
< 1µs. Do not leave this pin floating.
On the LTC1147L this pin serves as the feedback pin from
an external resistive divider used to set the output voltage.
GND (Pin 7):
Two independent ground lines must be
routed separately to: 1) the (–) terminal of C
OUT
, and 2) the
cathode of the Schottky diode and (–) terminal of C
IN
.
PDRIVE (Pin 8):
High current drive for the P-channel
MOSFET. Voltage swing at this pin is from V
IN
to ground.
FU CTIO AL DIAGRA
V
SLEEP
R
Q
S
C
25mV TO 150mV
–
+
5pF
V
OS
+
S
T
13k
I
TH
3
G
2
C
T
OFF-TIME
CONTROL
V
IN
SENSE
–
SHDN 6
REFERENCE
LTC1147 • FD
–
–
V
TH2
V
TH1
–
+
+
–
+
W
+
–
U
U
U
U
U
Pin 6 Connection Shown For LTC1147-3.3 and LTC1147-5; Changes Create LTC1147L.
SENSE
+
1 V
IN
5
V
FB
6
7 GND
SENSE
–
4
8 PDRIVE
1.25V
100k
5
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