LT1976 Datasheet PDF - Linear Technology

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LT1976
Linear Technology

Part Number LT1976
Description High Voltage 1.5A/ 200kHz Step-Down Switching Regulator with 100mA Quiescent Current
Page 24 Pages


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LT1976
High Voltage 1.5A, 200kHz
Step-Down Switching Regulator
with 100µA Quiescent Current
FEATURES
s Wide Input Range: 3.3V to 60V
s 1.5A Peak Switch Current
s Burst Mode® Operation: 100µA Quiescent Current**
s Low Shutdown Current: IQ < 1µA
s Power Good Flag with Programmable Threshold
s Load Dump Protection to 60V
s 200kHz Switching Frequency
s Saturating Switch Design: 0.2On-Resistance
s Peak Switch Current Maintained Over
Full Duty Cycle Range*
s 1.25V Feedback Reference Voltage
s Easily Synchronizable
s Soft-Start Capability
s Small 16-Pin Thermally Enhanced TSSOP Package
U
APPLICATIO S
s High Voltage Power Conversion
s 14V and 42V Automotive Systems
s Industrial Power Systems
s Distributed Power Systems
s Battery-Powered Systems
DESCRIPTIO
The LT®1976 is a 200kHz monolithic buck switching
regulator that accepts input voltages up to 60V. A high
efficiency 1.5A, 0.2switch is included on the die along
with all the necessary oscillator, control and logic cir-
cuitry. 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. 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 CSS pin to the output
provides a controlled output voltage ramp (soft-start). The
device also has a power good flag with a programmable
threshold and time-out and thermal shutdown protection.
The LT1976 is available in a 16-pin TSSOP package with
exposed pad leadframe for low thermal resistance.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a registered trademark of Linear Technology Corporation.
*U.S. Patent 6,498,466 **See Burst Mode Operation section for conditions
TYPICAL APPLICATIO
14V to 3.3V Step-Down Converter with
100µA No Load Quiescent Current
VIN
3.3V TO 60V
0.047µF
12.5k
4.7µF
100V
CER
100pF
1µF
VIN BOOST
SHDN
SW
0.33µF 33µH 4148
LT1976 0.1µF
10MQ100N
VC CSS
CT
SYNC
GND
VBIAS
FB
PGFB
PG
27pF
165k
1%
100k
1%
VOUT
3.3V
1A
100µF
6.3V
TANT
1976 TA01
Supply Current vs
Input Voltage
150
VOUT = 3.3V
TA = 25°C
125
100
75
50
25
0
0 10 20 30 40 50 60
INPUT VOLTAGE (V)
1976 F05
Efficiency vs Load Current
100
90
VOUT = 5V
80
TA = 25°C
70 VOUT = 3.3V
60
50
40
30
20
10
0
0.0001 0.001 0.01
0.1
LOAD CURRENT (A)
1
10
1976 TA02
1976f
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LT1976
ABSOLUTE AXI U RATI GS
(Note 1)
VIN, SHDN, BIAS ..................................................... 60V
BOOST Pin Above SW ............................................ 35V
BOOST Pin Voltage ................................................. 68V
SYNC, CSS, PGFB, FB ................................................ 6V
Operating JunctionTemperature Range
LT1976EFE (Note 2) ........................ – 40°C to 125°C
LT1976IFE (Note 2) ......................... – 40°C to 125°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
UW U
PACKAGE/ORDER I FOR ATIO
NC 1
SW 2
NC 3
VIN 4
NC 5
BOOST 6
TCAP 7
GND 8
TOP VIEW
16 PGOOD
15 SHDN
14 SYNC
13 PGFB
17
12 FB
11 VC
10 BIAS
9 CSS
ORDER PART
NUMBER
LT1976EFE
LT1976IFE
FE PACKAGE
16-LEAD PLASTIC TSSOP
TJMAX = 125°C, θJA = 45°C/W, θJC(PAD) = 10°C/W
EXPOSED PAD IS GND (PIN 17)
MUST BE SOLDERED TO GND (PIN 8)
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS The q denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TJ = 25°C. VIN = 12V, SHDN = 12V, BOOST = 15.3V, BIAS = 5V, FB/PGFB = 1.25V,
CSS/SYNC = 0V unless otherwise noted.
SYMBOL PARAMETER
CONDITIONS
MIN TYP MAX UNITS
VSHDN SHDN Threshold
q 1.2 1.3 1.4
V
ISHDN
SHDN Input Current
Minimum Input Voltage (Note 3)
SHDN = 12V
q
5 20
µA
q
2.4 3
V
IVINS Supply Shutdown Current
SHDN = 0V, BOOST = 0V, FB/PGFB = 0V
0.1 2
µA
Supply Sleep Current (Note 4)
BIAS = 0V, FB = 1.35V
FB = 1.35V
q
170 230
µA
q
45 75
µA
IVIN Supply Quiescent Current
Minimum BIAS Voltage (Note 5)
BIAS = 0V, FB = 1.15V, VC = 0.8V
BIAS = 5V, FB = 1.15V, VC = 0.8V
3.2 4.10
2.6 3.25
mA
mA
q
2.7 3
V
IBIASS
BIAS Sleep Current (Note 4)
q
110 180
µA
IBIAS BIAS Quiescent Current
Minimum Boost Voltage (Note 6)
SYNC = 3.3V
ISW = 1.5A
700 800
1.8 2.5
µA
V
Input Boost Current (Note 7)
VREF Reference Voltage (VREF)
ISW = 0.5A
ISW = 1.5A
3.3V < VVIN < 60V
10 15
40 50
q 1.225 1.25 1.275
mA
mA
V
IFB FB Input Bias Current
75 200
nA
EA Voltage Gain (Note 8)
900 V/V
EA Voltage gm
EA Source Current
dI(VC)= ±10µA
FB = 1.15V
500 650 800 µMho
25 40 55
µA
EA Sink Current
FB = 1.35V
20 30 40
µA
VC to SW gm
VC High Clamp
3
2.1 2.2 2.4
A/V
V
IPK SW Current Limit
q 1.5 2.4 3.5
A
1976f
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LT1976
ELECTRICAL CHARACTERISTICS The q denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TJ = 25°C. VIN = 12V, SHDN = 12V, BOOST = 15.3V, BIAS = 5V, FB/PGFB = 1.25V,
CSS/SYNC = 0V unless otherwise noted.
SYMBOL PARAMETER
CONDITIONS
MIN TYP MAX UNITS
Switch On Resistance (Note 9)
q
0.2 0.4
Switching Frequency
q 180 200 230
kHz
Maximum Duty Cycle
90 92
%
Minimum SYNC Amplitude
1.5 2.0
V
SYNC Frequency Range
600 kHz
SYNC Input Impedance
85 k
ICSS
IPGFB
VPGFB
ICT
VCT
CSS Current Threshold (Note 10)
PGFB Input Current
PGFB Voltage Threshold (Note 11)
CT Source Current (Note 11)
CT Sink Current (Note 11)
CT Voltage Threshold (Note 11)
PG Leakage (Note 11)
10 13 16
25 100
q 88 90 92
q3
3.6 5.5
12
1.16 1.2 1.24
0.1 1
µA
nA
%
µA
mA
V
µA
PG Sink Current (Note 11)
PGFB = 1V, PG = 400mV
120 200
µA
Note 1: Absolute Maximum Ratings are those values beyond which the life of
a device may be impaired.
Note 2: The LT1976EFE is 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 is guaranteed and tested over the full –40°C to 125°C operating
junction temperature range.
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 VIN 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 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 IBIAS 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 VC swing from 1.15V to 750mV.
Note 9: Switch on resistance is calculated by dividing VIN to SW voltage by the
forced current (1.5A). See Typical Performance Characteristics for the graph
of switch voltage at other currents.
Note 10: The CSS threshold is defined as the value of current sourced into the
CSS pin which results in an increase in sink current from the VC pin. See the
Soft-Start section in Applications Information.
Note 11: The PGFB threshold is defined as the percentage of VREF voltage
which causes the current source output of the CT pin to change from
sinking (below threshold) to sourcing current (above threshold). When
sourcing current, the voltage on the CT 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 CT clamp is inactive the PG pin will
be set active low with a current sink capability of 200µA.
1976f
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LT1976
TYPICAL PERFOR A CE CHARACTERISTICS
FB Voltage
1.30
1.29
1.28
1.27
1.26
1.25
1.24
1.23
1.22
1.21
1.20
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
1976 G01
SHDN Pin Current
5.5
TJ = 25°C
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0
0 10 20 30 40
SHDN VOLTAGE (V)
50 60
1976 G04
Bias Sleep Current
200
180
160
140
120
100
80
60
40
20
0
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
1976 G07
Oscillator Frequency
250
240
230
220
210
200
190
180
170
160
150
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
1976 G02
Shutdown Supply Current
25
20
VIN = 60V
15
10
5
VIN = 42V VIN = 12V
0
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
1976 G05
PGFB Threshold
1.20
1.18
1.16
1.14
1.12
1.10
1.08
1.06
1.04
1.02
1.00
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
1976 G08
SHDN Threshold
1.40
1.35
1.30
1.25
1.20
0.15
1.10
1.05
1.00
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
1976 G03
Sleep Mode Supply Current
200
180
160 VBIAS = 0V
140
120
100
80
60 VBIAS = 5V
40
20
0
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
1976 G06
PG Sink Current
250
200
150
100
50
0
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
1976 G08
1976f
4



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