LT1976/LT1976B
High Voltage 1.5A, 200kHz
Step-Down Switching Regulator
with 100μA Quiescent Current
FEATURES
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DESCRIPTIO
Wide Input Range: 3.3V to 60V
1.5A Peak Switch Current (LT1976)
100μA Quiescent Current (LT1976)**
1.6mA Quiescent Current (LT1976B)
Low Shutdown Current: I
Q
< 1μA
Power Good Flag with Programmable Threshold
Load Dump Protection to 60V
200kHz Switching Frequency
Saturating Switch Design: 0.2Ω On-Resistance
Peak Switch Current Maintained Over
Full Duty Cycle Range*
1.25V Feedback Reference Voltage
Easily Synchronizable
Soft-Start Capability
Small 16-Pin Thermally Enhanced TSSOP Package
The LT
®
1976/LT1976B are 200kHz monolithic step-down
switching regulators that accept input voltages up to 60V.
A high efficiency 1.5A, 0.2Ω switch is included on the die
along with all the necessary oscillator, control and logic
circuitry. Current mode topology is used for fast transient
response and good loop stability.
Innovative design techniques along with a new high volt-
age process achieve high efficiency over a wide input
range. Efficiency is maintained over a wide output current
range by employing Burst Mode operation at low currents,
utilizing the output to bias the internal circuitry, and by
using a supply boost capacitor to fully saturate the power
switch. The LT1976B does not shift into Burst Mode
operation at low currents, eliminating low frequency out-
put ripple at the expense of efficiency. Patented circuitry
maintains peak switch current over the full duty cycle
range.* Shutdown reduces input supply current to less
than 1μA. External synchronization can be implemented
by driving the SYNC pin with logic-level inputs. A single
capacitor from the C
SS
pin to the output provides a
controlled output voltage ramp (soft-start). The devices
also have a power good flag with a programmable thresh-
old and time-out and thermal shutdown protection.
The LT1976/LT1976B are available in a 16-pin TSSOP
package with Exposed Pad leadframe for low thermal
resistance.
APPLICATIO S
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High Voltage Power Conversion
14V and 42V Automotive Systems
Industrial Power Systems
Distributed Power Systems
Battery-Powered Systems
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
Burst Mode is a registered trademark of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
*Protected by U.S. Patents, including 6498466
**See Burst Mode Operation section for conditions
TYPICAL APPLICATIO
V
IN
3.3V TO 60V
V
IN
SHDN
LT1976
V
C
1500pF
10k
1μF
330pF
C
T
SYNC
GND
C
SS
V
BIAS
FB
PGFB
PG
47pF
BOOST
14V to 3.3V Step-Down Converter with
100μA No Load Quiescent Current
4.7μF
100V
CER
0.33μF 33μH
SW
0.1μF
10MQ60N
4148
SUPPLY CURRENT (μA)
LT1976 Supply Current vs
Input Voltage
150
V
OUT
3.3V
1A
V
OUT
= 3.3V
T
A
= 25°C
125
EFFICIENCY (%)
100
75
50
25
0
165k
1%
100k
1%
100μF
6.3V
TANT
1976 TA01
0
10
30
40
20
INPUT VOLTAGE (V)
50
60
1976 F05
U
LT1976 Efficiency and Power
Loss vs Load Current
100
EFFICIENCY
75
5V
3.3V
50
TYPICAL
POWER LOSS
25
0.01
0.1
1
POWER LOSS (W)
10
0
0.1
1
0.001
100
1000 10000
10
1976 TA02
LOAD CURRENT (mA)
U
U
1976bfg
1
LT1976/LT1976B
ABSOLUTE
(Note 1)
AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
NC
SW
NC
V
IN
NC
BOOST
C
T
GND
1
2
3
4
5
6
7
8
17
16 PG
15 SHDN
14 SYNC
13 PGFB
12 FB
11 V
C
10 BIAS
9
C
SS
V
IN
, SHDN, PG, BIAS .............................................. 60V
BOOST Pin Above SW ............................................ 35V
BOOST Pin Voltage ................................................. 68V
SYNC, C
SS
, PGFB, FB ................................................ 6V
Operating JunctionTemperature Range
LT1976EFE/LT1976BEFE (Note 2) ... – 40°C to 125°C
LT1976IFE/LT1976BIFE (Note 2) ..... – 40°C to 125°C
LT1976HFE (Note 2) ........................ – 40°C to 140°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
ORDER PART
NUMBER
LT1976EFE
LT1976IFE
LT1976HFE
LT1976BEFE
LT1976BIFE
FE PART MARKING
1976EFE
1976IFE
1976HFE
1976BEFE
1976BIFE
FE PACKAGE
16-LEAD PLASTIC TSSOP
θ
JA
= 45°C/W,
θ
JC(PAD)
= 10°C/W
EXPOSED PAD IS GND (PIN 17)
MUST BE SOLDERED TO GND (PIN 8)
Order Options
Tape and Reel: Add #TR
Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF
Lead Free Part Marking: http://www.linear.com/leadfree/
Consult LTC Marketing for parts specified with wider operating temperature ranges.
The
●
denotes the specifications which apply over the full –40°C to 125°C
operating temperature range, otherwise specifications are at T
J
= 25°C. V
IN
= 12V, SHDN = 12V, BOOST = 15.3V, BIAS = 5V,
FB/PGFB = 1.25V, C
SS
/SYNC = 0V unless otherwise noted.
SYMBOL
V
SHDN
I
SHDN
I
VINS
PARAMETER
SHDN Threshold
SHDN Input Current
Minimum Input Voltage (Note 3)
Supply Shutdown Current
Supply Sleep Current (Note 4) (LT1976)
Supply Quiescent Current
Minimum BIAS Voltage (Note 5)
BIAS Sleep Current (Note 4) (LT1976)
BIAS Quiescent Current
Minimum Boost Voltage (Note 6)
Input Boost Current (Note 7)
Reference Voltage (V
REF
)
FB Input Bias Current
EA Voltage Gain (Note 8)
EA Voltage g
m
EA Source Current
EA Sink Current
V
C
to SW g
m
V
C
High Clamp
V
C
Switching Threshold (LT1976B)
CONDITIONS
●
ELECTRICAL CHARACTERISTICS
MIN
1.2
SHDN = 12V
●
●
I
VIN
SHDN = 0V, BOOST = 0V, FB/PGFB = 0V
BIAS = 0V, FB = 1.35V
●
●
FB = 1.35V
BIAS = 0V, FB = 1.15V, V
C
= 0.8V (V
C
= 0V LT1976B)
BIAS = 5V, FB = 1.15V, V
C
= 0.8V (V
C
= 0V LT1976B)
●
●
I
BIASS
I
BIAS
V
REF
I
FB
SYNC = 3.3V
I
SW
= 1.5A
I
SW
= 1.5A
3.3V < V
VIN
< 60V
●
1.225
dI(V
C
)=
±10μA
FB = 1.15V
FB = 1.35V
400
20
15
2.1
0.1
●
TYP
1.3
5
2.4
0.1
170
45
3.2
2.6
2.7
110
700
1.8
40
1.25
75
900
650
40
30
3
2.2
0.4
MAX
1.4
20
3
2
230
75
4.10
3.25
3
180
800
2.5
50
1.275
200
800
55
40
2.4
0.8
UNITS
V
μA
V
μA
μA
μA
mA
mA
V
μA
μA
V
mA
V
nA
V/V
μMho
μA
μA
A/V
V
V
1976bfg
2
U
W
U
U
W W
W
LT1976/LT1976B
The
●
denotes the specifications which apply over the full –40°C to 125°C
operating temperature range, otherwise specifications are at T
J
= 25°C. V
IN
= 12V, SHDN = 12V, BOOST = 15.3V, BIAS = 5V,
FB/PGFB = 1.25V, C
SS
/SYNC = 0V unless otherwise noted.
SYMBOL
I
PK
PARAMETER
SW Current Limit
Switch On Resistance (Note 9)
Switching Frequency
Maximum Duty Cycle
Minimum SYNC Amplitude
SYNC Frequency Range
SYNC Input Impedance
I
CSS
I
PGFB
V
PGFB
I
CT
V
CT
C
SS
Current Threshold (Note 10)
PGFB Input Current
PGFB Voltage Threshold (Note 11)
C
T
Source Current (Note 11)
C
T
Sink Current (Note 11)
C
T
Voltage Threshold (Note 11)
PG Leakage (Note 11)
PG Sink Current (Note 11)
PG = 12V
PGFB = 1V, PG = 400mV
120
●
●
ELECTRICAL CHARACTERISTICS
CONDITIONS
LT1976
LT1976B
BOOST = OPEN
●
●
●
MIN
1.5
1.2
180
90
230
TYP
2.4
2.5
0.2
200
92
1.5
600
100
13
25
90
3.6
2
1.2
0.1
200
MAX
3.5
4
0.4
230
2.0
UNITS
A
A
Ω
kHz
%
V
kHz
kΩ
SYNC = 0.5V
FB = 0V
7
88
2
1
1.16
20
100
92
5.5
1.26
1
μA
nA
%
μA
mA
V
μA
μA
The
●
denotes the specifications which apply over the full –40°C to 140°C operating temperature range, otherwise specifications are
at T
J
= 25°C. V
IN
= 12V, SHDN = 12V, BOOST = 15.3V, BIAS = 5V, FB/PGFB = 1.25V, C
SS
/SYNC = 0V unless otherwise noted.
SYMBOL
V
SHDN
I
SHDN
I
VINS
PARAMETER
SHDN Threshold
SHDN Input Current
Minimum Input Voltage (Note 3)
Supply Shutdown Current
Supply Sleep Current (Note 4) (LT1976)
I
VIN
Supply Quiescent Current
Minimum BIAS Voltage (Note 5)
I
BIASS
I
BIAS
BIAS Sleep Current (Note 4)
BIAS Quiescent Current
Minimum Boost Voltage (Note 6)
Input Boost Current (Note 7)
V
REF
I
FB
Reference Voltage (V
REF
)
FB Input Bias Current
EA Voltage Gain (Note 8)
EA Voltage g
m
EA Source Current
EA Sink Current
V
C
to SW g
m
V
C
High Clamp
2.1
dI(V
C
)=
±10μA
FB = 1.15V
FB = 1.35V
400
20
15
SYNC = 3.3V
I
SW
= 1.5A
I
SW
= 1.5A
3.3V < V
VIN
< 60V
●
CONDITIONS
●
MIN
1.2
●
●
TYP
1.3
5
2.4
0.1
170
45
3.2
2.6
MAX
1.4
20
3
2
300
100
4.10
3.25
3
180
800
2.5
50
1.288
200
800
55
40
2.4
UNITS
V
μA
V
μA
μA
μA
mA
mA
V
μA
μA
V
mA
V
nA
V/V
μMho
μA
μA
A/V
V
1976bfg
SHDN = 12V
SHDN = 0V, BOOST = 0V, FB/PGFB = 0V
BIAS = 0V, FB = 1.35V
FB = 1.35V
BIAS = 0V, FB = 1.15V, V
C
= 0.8V
BIAS = 5V, FB = 1.15V, V
C
= 0.8V
●
●
●
●
2.7
110
700
1.8
40
1.212
1.25
75
900
650
40
30
3
2.2
3
LT1976/LT1976B
The
●
denotes the specifications which apply over the full –40°C to 140°C
operating temperature range, otherwise specifications are at T
J
= 25°C. V
IN
= 12V, SHDN = 12V, BOOST = 15.3V, BIAS = 5V,
FB/PGFB = 1.25V, C
SS
/SYNC = 0V unless otherwise noted.
SYMBOL
I
PK
PARAMETER
SW Current Limit
Switch On Resistance (Note 9)
Switching Frequency
Maximum Duty Cycle
Minimum SYNC Amplitude
SYNC Frequency Range
SYNC Input Impedance
I
CSS
I
PGFB
V
PGFB
I
CT
V
CT
C
SS
Current Threshold (Note 10)
PGFB Input Current
PGFB Voltage Threshold (Note 11)
C
T
Source Current (Note 11)
C
T
Sink Current (Note 11)
C
T
Voltage Threshold (Note 11)
PG Leakage (Note 11)
PG Sink Current (Note 11)
PG = 12V
PGFB = 1V, PG = 400mV
120
●
●
●
ELECTRICAL CHARACTERISTICS
CONDITIONS
MIN
TYP
2.4
0.2
MAX
0.6
260
2.0
UNITS
A
Ω
kHz
%
V
kHz
kΩ
BOOST = OPEN
●
150
90
230
200
92
1.5
600
85
13
25
90
3.6
2
1.2
0.1
200
SYNC = 0.5V
7
87
1.5
1
1.16
20
100
93
5.5
1.26
1
μA
nA
%
μA
mA
V
μA
μA
Note 1:
Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2:
The LT1976EFE/LT1976BEFE are guaranteed to meet performance
specifications from 0°C to 125°C junction temperature. Specifications over
the –40°C to 125°C operating junction temperature range are assured by
design, characterization and correlation with statistical process controls.
The LT1976IFE/LT1976BIFE/LT1976HFE are guaranteed and tested over
the full –40°C to 125°C operating junction temperature range. The
LT1976HFE is also tested to the LT1976HFE electrical characteristics table
at 140°C operating junction temperature. High junction temperatures
degrade operating lifetimes.
Note 3:
Minimum input voltage is defined as the voltage where switching
starts. Actual minimum input voltage to maintain a regulated output will
depend upon output voltage and load current. See Applications
Information.
Note 4:
Supply input current is the quiescent current drawn by the input
pin. Its typical value depends on the voltage on the BIAS pin and operating
state of the LT1976. With the BIAS pin at 0V, all of the quiescent current
required to operate the LT1976 will be provided by the V
IN
pin. With the
BIAS voltage above its minimum input voltage, a portion of the total
quiescent current will be supplied by the BIAS pin. Supply sleep current
for the LT1976 is defined as the quiescent current during the “sleep”
portion of Burst Mode operation. See Applications Information for
determining application supply currents.
Note 5:
Minimum BIAS voltage is the voltage on the BIAS pin when I
BIAS
is
sourced into the pin.
Note 6:
This is the minimum voltage across the boost capacitor needed to
guarantee full saturation of the internal power switch.
Note 7:
Boost current is the current flowing into the BOOST pin with the
pin held 3.3V above input voltage. It flows only during switch on time.
Note 8:
Gain is measured with a V
C
swing from 1.15V to 750mV.
Note 9:
Switch on resistance is calculated by dividing V
IN
to SW voltage by
the forced current (1.5A LT1976, 1.2A LT1976B). See Typical Performance
Characteristics for the graph of switch voltage at other currents.
Note 10:
The C
SS
threshold is defined as the value of current sourced into
the C
SS
pin which results in an increase in sink current from the V
C
pin.
See the Soft-Start section in Applications Information.
Note 11:
The PGFB threshold is defined as the percentage of V
REF
voltage
which causes the current source output of the C
T
pin to change from
sinking (below threshold) to sourcing current (above threshold). When
sourcing current, the voltage on the C
T
pin rises until it is clamped
internally. When the clamp is activated, the output of the PG pin will be set
to a high impedance state. When the C
T
clamp is inactive the PG pin will
be set active low with a current sink capability of 200μA.
1976bfg
4
LT1976/LT1976B
TYPICAL PERFOR A CE CHARACTERISTICS
LT1976 Efficiency and Power Loss
vs Load Current
100
EFFICIENCY
75
EFFICIENCY (%)
5V
3.3V
50
TYPICAL
POWER LOSS
25
0.01
0.1
1
POWER LOSS (W)
75
10
100
EFFICIENCY
1
EFFICIENCY (%)
VOLTAGE (V)
0
0.1
1
0.001
100
1000 10000
10
1976 TA02
LOAD CURRENT (mA)
Oscillator Frequency
250
240
230
FREQUENCY (kHz)
220
210
200
190
180
170
160
150
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
1976 G02
VOLTAGE (V)
1.25
1.20
0.15
1.10
1.05
1.00
–50 –25
CURRENT (μA)
Shutdown Supply Current
25
240
220
20
V
IN
= 60V
200
180
CURRENT (μA)
CURRENT (μA)
CURRENT (μA)
15
10
5
V
IN
= 42V
0
–50 –25
0
V
IN
= 12V
25 50 75 100 125 150
TEMPERATURE (°C)
1976 G05
U W
LT1976B Efficiency and Power
Loss vs Load Current
10
FB Voltage
1.30
1.29
1.28
1.27
1.26
1.25
1.24
1.23
1.22
1.21
POWER LOSS (W)
5V
3.3V
50
TYPICAL
POWER LOSS
25
0.01
0.1
0
0.1
1
100
1000
10
LOAD CURRENT (mA)
0.001
10000
1976 G25
1.20
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
1976 G01
SHDN Threshold
1.40
1.35
1.30
5.5
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0
SHDN Pin Current
T
J
= 25°C
0
25 50 75 100 125 150
TEMPERATURE (°C)
1976 G03
0
10
30
40
20
SHDN VOLTAGE (V)
50
60
1976 G04
LT1976 Sleep Mode Supply
Current
200
180
V
BIAS
= 0V
LT1976 Bias Sleep Current
160
140
120
100
80
60
40
20
160
140
120
100
80
60
40
20
0
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
1976 G06
V
BIAS
= 5V
0
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
1976 G07
1976bfg
5
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