1
LTC1159/LTC1159-3.3/LTC1159-5
S
FEATURE
D
U
ESCRIPTIO
s
Operation from 4V to 40V Input Voltage
s
Ultra-High Efficiency: Up to 95%
s
20
A Supply Current in Shutdown
s
High Efficiency Maintained Over Wide Current Range
s
Current Mode Operation for Excellent Line and Load
Transient Response
s
Very Low Dropout Operation: 100% Duty Cycle
s
Short-Circuit Protection
s
Synchronous FET Switching for High Efficiency
s
Adaptive Non-Overlap Gate Drives
s
Available in SSOP and SO Packages
The LTC
1159 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 complemen-
tary power MOSFETs at switching frequencies up to 250kHz
using a constant off-time current-mode architecture.
A separate pin and on-board switch allow the MOSFET
driver power to be derived from the regulated output
voltage providing significant efficiency improvement when
operating at high input voltages. The constant off-time
current-mode architecture maintains constant ripple cur-
rent in the inductor and provides excellent line and load
transient response. The output current level is user pro-
grammable via an external current sense resistor.
The LTC1159 automatically switches to power saving
Burst Mode operation when load current drops below
approximately 15% of maximum current. Standby current
is only 300
A while still regulating the output and shut-
down current is a low 20
A.
High Efficiency Synchronous
Step-Down Switching Regulators
s
Step-Down and Inverting Regulators
s
Notebook and Palmtop Computers
s
Portable Instruments
s
Battery-Operated Digital Devices
s
Industrial Power Distribution
s
Avionics Systems
s
Telecom Power Supplies
U
S
A
O
PPLICATI
Figure 1. High Efficiency Step-Down Regulator
LOAD CURRENT (A)
0.02
60
EFFICIENCY (%)
70
80
100
0.2
2
LTC1159 TA01
90
V
IN
= 10V
V
IN
= 20V
FIGURE 1 CIRCUIT
LTC1159-5 Efficiency
0.15
F
V
IN
CAP
P-DRIVE
EXTV
CC
LTC1159-5
SHDN1
I
TH
C
T
S-GND
P-GATE
V
CC
V
CC
SHDN2
SENSE
SENSE
+
P-GND
N-GATE
0.01
F
Si9410DY
0.1
F
1N4148
V
IN
Si9435DY
D1
MBRS140T3
L*
33
H
R
SENSE
0.05
V
OUT
5V/2A
+
C
OUT
220
F
+
C
IN
100
F
100V
+
3.3
F
0V = NORMAL
>2V = SHUTDOWN
3300pF
C
T
300pF
1k
LTC1159 F01
*COILTRONICS CTX33-4-MP
U
A
O
PPLICATI
TYPICAL
Burst Mode is a trademark of Linear Technology Corporation.
, LTC and LT are registered trademarks of Linear Technology Corporation.
2
LTC1159/LTC1159-3.3/LTC1159-5
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
V
FB
Feedback Voltage (LTC1159 Only)
q
1.21
1.25
1.29
V
I
FB
Feedback Current (LTC1159 Only)
q
0.2
A
V
OUT
Regulated Output Voltage
V
IN
= 9V
LTC1159-3.3
I
LOAD
= 700mA
q
3.23
3.33
3.43
V
LTC1159-5
I
LOAD
= 700mA
q
4.90
5.05
5.20
V
V
OUT
Output Voltage Line Regulation
V
IN
= 9V to 40V
40
0
40
mV
Output Voltage Load Regulation
LTC1159-3.3
5mA < I
LOAD
< 2A
q
40
65
mV
LTC1159-5
5mA < I
LOAD
< 2A
q
60
100
mV
Burst Mode Output Ripple
I
LOAD
= 0A
50
mV
P-P
I
IN
V
IN
Pin Current (Note 3)
Normal Mode
V
IN
= 12V, EXTV
CC
= 5V
200
A
V
IN
= 40V, EXTV
CC
= 5V
300
A
Shutdown
V
IN
= 12V, V
SHDN2
= 2V
15
A
V
IN
= 40V, V
SHDN2
= 2V
25
A
I
EXTVCC
EXTV
CC
Pin Current (Note 3)
EXTV
CC
= 5V, Sleep Mode
250
A
V
CC
Internal Regulator Voltage
V
IN
= 12V to 40V, EXTV
CC
= 0V, I
CC
= 10mA
q
4.25
4.5
4.75
V
V
IN
V
CC
V
CC
Dropout Voltage
V
IN
= 4V, EXTV
CC
= Open, I
CC
= 10mA
300
400
mV
A
U
G
W
A
W
U
W
A
R
BSOLUTE
XI
TI
S
Input Supply Voltage (Pin 2)...................... 15V to 60V
V
CC
Output Current (Pin 3) .................................. 50mA
Continuous Pin Currents (Any Pin) ...................... 50mA
Sense Voltages ......................................... 0.3V to 13V
Shutdown Voltages ................................................... 7V
EXTV
CC
Input Voltage ............................................. 15V
Operating Temperature Range .................... 0
C to 70
C
Extended Commercial
Temperature Range ............................... 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
W
U
U
PACKAGE/ORDER I FOR ATIO
LTC1159CG
LTC1159CG-3.3
LTC1159CG-5
ORDER PART
NUMBER
T
JMAX
= 125
C,
JA
= 135
C/ W
LTC1159CN
LTC1159CN-3.3
LTC1159CN-5
LTC1159CS
LTC1159CS-3.3
LTC1159CS-5
ORDER PART
NUMBER
1
2
3
4
5
6
7
8
9
10
TOP VIEW
G PACKAGE
20-LEAD PLASTIC SSOP
20
19
18
17
16
15
14
13
12
11
P-GATE
V
IN
V
CC
P-DRIVE
P-DRIVE
V
CC
V
CC
C
T
I
TH
SENSE
CAP
SHDN2
EXTV
CC
P-GND
N-GATE
P-GND
S-GND
SHDN1
V
FB
SENSE
+
Consult factory for Industrial and Military grade parts.
ELECTRICAL C
C
HARA TERISTICS
T
A
= 25
C, V
IN
= 12V, V
SHDN1
= 0V (Note 2), unless otherwise noted.
1
2
3
4
5
6
7
8
TOP VIEW
S PACKAGE
16-LEAD PLASTIC SO
N PACKAGE
16-LEAD PDIP
16
15
14
13
12
11
10
9
P-GATE
V
IN
V
CC
P-DRIVE
V
CC
C
T
I
TH
SENSE
CAP
SHDN2
EXTV
CC
N-GATE
P-GND
S-GND
SENSE
+
*FIXED OUTPUT VERSIONS
V
FB
(SHDN1)*
T
JMAX
= 125
C,
JA
= 80
C/ W (N)
T
JMAX
= 125
C,
JA
= 110
C/ W (S)
3
LTC1159/LTC1159-3.3/LTC1159-5
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
V
EXT
V
CC
EXTV
CC
Switch Drop
V
IN
= 12V, EXTV
CC
= 5V, I
SWITCH
= 10mA
250
350
mV
V
P-GATE
V
IN
P-Gate to Source Voltage (Off)
V
IN
= 12V
0.2
0
V
V
IN
= 40V
0.2
0
V
V
SENSE
+
Current Sense Threshold Voltage
V
SENSE
LTC1159
V
SENSE
= 5V, V
FB
= 1.32V (Forced)
25
mV
V
SENSE
= 5V, V
FB
= 1.15V (Forced)
q
130
150
170
mV
LTC1159-3.3
V
SENSE
= 3.4V (Forced)
25
mV
V
SENSE
= 3.1V (Forced)
q
130
150
170
mV
LTC1159-5
V
SENSE
= 5.2V (Forced)
25
mV
V
SENSE
= 4.7V (Forced)
q
130
150
170
mV
V
SNDN1
SHDN1 Threshold
LTC1159CG, LTC1159-3.3, LTC1159-5
0.6
0.8
2
V
V
SHDN2
SHDN2 Threshold
0.8
1.4
2
V
I
SHDN2
Shutdown 2 Input Current
V
SHDN2
= 5V
12
20
A
I
CT
C
T
Pin Discharge Current
V
OUT
in Regulation
50
70
90
A
V
OUT
= 0V
2
10
A
t
OFF
Off-Time (Note 4)
C
T
= 390pF, I
LOAD
= 700mA, V
IN
= 10V
4
5
6
s
t
r
, t
f
Driver Output Transition Times
C
L
= 3000pF (Pins P-Drive and N-Gate), V
IN
= 6V
100
200
ns
ELECTRICAL C
C
HARA TERISTICS
T
A
= 25
C, V
IN
= 12V, V
SHDN1
= 0V (Note 2), unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
V
FB
Feedback Voltage (LTC1159 Only)
1.2
1.25
1.3
V
V
OUT
Regulated Output Voltage
V
IN
= 9V
LTC1159-3.3
I
LOAD
= 700mA
3.17
3.30
3.43
V
LTC1159-5
I
LOAD
= 700mA
4.85
5.05
5.25
V
I
IN
V
IN
Pin Current (Note 3)
Normal
V
IN
= 12V, EXTV
CC
= 5V
200
A
V
IN
= 40V, EXTV
CC
= 5V
300
A
Shutdown
V
IN
= 12V, V
SHDN2
= 2V
15
A
V
IN
= 40V, V
SHDN2
= 2V
25
A
I
EXTVCC
EXTV
CC
Pin Current (Note 3)
EXTV
CC
= 5V, Sleep Mode
250
A
V
CC
Internal Regulator Voltage
V
IN
= 12V to 40V, EXTV
CC
= 0V, I
CC
= 10mA
4.5
V
V
SENSE
+
Current Sense Threshold Voltage
Low Threshold (Forced)
25
mV
V
SENSE
High Threshold (Forced)
125
150
175
mV
V
SHDN2
SHDN2 Threshold
0.8
1.4
2
V
t
OFF
Off-Time (Note 4)
C
T
= 390pF, I
LOAD
= 700mA, V
IN
= 10V
3.5
5
6.5
s
40
C
T
A
85
C (Note 5)
The
q
denotes specifications which apply over the full operating
temperature range.
Note 1: T
J
is calculated from the ambient temperature T
A
and power
dissipation P
D
according to the following formulas:
LTC1159CG, LTC1159CG-3.3, LTC1159CG-5: T
J
= T
A
+ (P
D
135
C/W)
LTC1159CN, LTC1159CN-3.3, LTC1159CN-5: T
J
= T
A
+ (P
D
80
C/W)
LTC1159CS, LTC1159CS-3.3, LTC1159CS-5: T
J
= T
A
+ (P
D
110
C/W)
Note 2: On LTC1159 versions which have a SHDN1 pin, it must be at
ground potential for testing.
Note 3: The LTC1159 V
IN
and EXTV
CC
current measurements exclude
MOSFET driver currents. When V
CC
power is derived from the output via
EXTV
CC
, the input current increases by (I
GATECHG
Duty Cycle)/(Efficiency).
See Typical Performance Characteristics and Applications Information.
Note 4: In applications where R
SENSE
is placed at ground potential, the off-
time increases approximately 40%.
Note 5: The LTC1159, LTC1159-3.3, and LTC1159-5 are not tested and
not quality assurance sampled at 40
C and 85
C. These specifications
are guaranteed by design and/or correlation.
Note 6: The logic-level power MOSFETs shown in Figure 1 are rated for
V
DS(MAX)
= 30V. For operation at V
IN
> 30V, use standard threshold
MOSFETs with EXTV
CC
powered from a 12V supply. See Applications
Information.
4
LTC1159/LTC1159-3.3/LTC1159-5
C
C
HARA TERISTICS
U
W
A
TYPICAL PERFOR
CE
Load Regulation
Efficiency vs Input Voltage
Line Regulation
Operating Frequency
vs (V
IN
V
OUT
)
EXTV
CC
Switch Drop
Current Sense Threshold Voltage
EXTV
CC
Pin Current
V
IN
Pin Current
Off-Time vs V
OUT
INPUT VOLTAGE (V)
0
80
EFFICIENCY (%)
85
90
95
100
5
10
15
20
LTC1159 TPC01
25
30
35
40
FIGURE 1 CIRCUIT
I
LOAD
= 1A
NOTE 6
LOAD CURRENT (A)
0
100
V
OUT
(mV)
80
60
40
20
0
20
0.5
1.0
1.5
2.0
LTC1159 TPC03
2.5
FIGURE 1 CIRCUIT
V
IN
= 24V
INPUT VOLTAGE (V)
0
EXTV
CC
CURRENT (mA)
6
8
10
15
25
40
LTC1159 TPC04
4
2
0
5
10
20
30
35
FIGURE 1 CIRCUIT
NOTE 6
I
LOAD
= 1A
I
LOAD
= 100mA
I
LOAD
= 0
INPUT VOLTAGE (V)
0
SUPPLY CURRENT (
A)
300
400
500
15
25
40
LTC1159 TPC05
200
100
0
5
10
20
30
35
FIGURE 1 CIRCUIT
NOTE 6
NORMAL
V
SHDN2
= 2V
(V
IN
V
OUT
) VOLTAGE (V)
0
NORMALIZED FREQUENCY
1.0
1.5
20
LTC1159 TPC06
0.5
0
5
10
15
25
2.0
V
OUT
= 5V
T = 70C
T = 0C
T = 25C
SWITCH CURRENT (mA)
0
0
EXTV
CC
V
CC
(mV)
100
200
300
400
500
600
5
10
15
20
LTC1159 TPC07
OUTPUT VOLTAGE (V)
1
OFF-TIME (
s)
40
50
60
5
LTC1159 TPC08
30
20
0
2
3
4
10
80
70
0
LTC1159-5
LTC1159-3.3
TEMPERATURE (C)
20
SENSE VOLTAGE (mV)
80
100
120
100
LTC1159 TPC09
60
40
0
40
60
80
20
160
140
0
MAXIMUM
THRESHOLD
MINIMUM
THRESHOLD
INPUT VOLTAGE (V)
0
60
V
OUT
(mV)
40
20
0
20
10
20
30
40
LT1159 TPC02
40
60
5
15
25
35
FIGURE 1 CIRCUIT
I
LOAD
= 1A
NOTE 6
5
LTC1159/LTC1159-3.3/LTC1159-5
PI FU CTIO S
U
U
U
Sense
+
: The (+) Input for the Current Comparator. A built-
in offset between the Sense
+
and Sense
pins, in conjunc-
tion with R
SENSE
, sets the current trip threshold.
N-Gate: High Current Drive for the Bottom N-Channel
MOSFET. The N-Gate pin swings from ground to V
CC
.
P-Gate: Level-Shifted Gate Drive Signal for the Top
P-Channel MOSFET. The voltage swing at the P-gate pin is
from V
IN
to V
IN
V
CC
.
P-Drive: High Current Gate Drive for the Top P-Channel
MOSFET. The P-drive pin(s) swing(s) from V
CC
to ground.
CAP: Charge Compensation Pin. A capacitor to V
CC
pro-
vides charge required by the P-gate level-shift capacitor
during supply transitions.
The charge compensation ca-
pacitor must be larger than the gate drive capacitor.
SHDN1: This pin shuts down the control circuitry only (V
CC
is not affected). Taking SHDN1 pin high turns off the
control circuitry and holds both MOSFETs off. This pin
must be at ground potential for normal operation.
SHDN2: Master Shutdown Pin. Taking SHDN2 high shuts
down V
CC
and all control circuitry.
The LTC1159 uses a current mode, constant off-time
architecture to synchronously switch an external pair of
complementary power MOSFETs. Operating frequency is
set by an external capacitor at the C
T
pin.
The output voltage is sensed either by an internal voltage
divider connected to the Sense
pin (LTC1159-3.3 and
LTC1159-5) or an external divider returned to the V
FB
pin
(LTC1159). A voltage comparator V, and a gain block G,
compare the divided output voltage with a reference
voltage of 1.25V. To optimize efficiency, the LTC1159
automatically switches between two modes of operation,
burst and continuous.
A low dropout 4.5V regulator provides the operating volt-
age V
CC
for the MOSFET drivers and control circuitry
during start-up. During normal operation, the LTC1159
family powers the drivers and control from the output via
the EXTV
CC
pin to improve efficiency. The N-gate pin is
referenced to ground and drives the N-channel MOSFET
(Refer to Functional Diagram)
gate directly. The P-channel gate drive must be referenced
to the main supply input V
IN
, which is accomplished by
level-shifting the P-drive signal via an internal 550k resis-
tor and external capacitor.
During the switch "ON" cycle in continuous mode,
current comparator C monitors the voltage between the
Sense
+
and Sense
pins connected across an external
shunt in series with the inductor. When the voltage
across the shunt reaches its threshold value, the P-gate
output is switched to V
IN
, turning off the P-channel
MOSFET. The timing capacitor C
T
is now allowed to
discharge at a rate determined by the off-time controller.
The discharge current is made proportional to the
output voltage to model the inductor current, which
decays at a rate which is also proportional to the output
voltage. While the timing capacitor is discharging, the
N-gate output is high, turning on the N-channel
MOSFET.
OPERATIO
U
V
IN
: Main Supply Input Pin.
S-GND: Small Signal Ground. Must be routed separately
from other grounds to the () terminal of C
OUT
.
P-GND: Driver Power Grounds. Connect to source of N-
channel MOSFET and the () terminal of C
IN
.
V
CC
: Outputs of internal 4.5V linear regulator, EXTV
CC
switch, and supply inputs for driver and control circuits.
The driver and control circuits are powered from the higher
of the 4.5V regulator or EXTV
CC
voltage. Must be closely
decoupled to power ground.
C
T
: External capacitor C
T
from this pin to ground sets the
operating frequency. (The frequency is also dependent on
the ratio V
OUT
/V
IN
.)
I
TH
: Gain Amplifier Decoupling Point. The current com-
parator threshold increases with the I
TH
pin voltage.
V
FB
: For the LTC1159 adjustable version, the V
FB
pin
receives the feedback voltage from an external resistive
divider used to set the output voltage.
Sense
: Connects to internal resistive divider which sets
the output voltage in fixed output versions. The Sense
pin
is also the () input of the current comparator.
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