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LT1578IS8-2.5#PBF

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1
LT1578/LT1578-2.5
1.5A, 200kHz Step-Down
Switching Regulator
3.3V Buck Converter
Efficiency vs Load Current
■
1.5A Switch Current
■
High Efficiency—Low Loss 0.2Ω Switch
■
Constant 200kHz Switching Frequency
■
4V to 15V Input VoltageRange
■
Minimum Output: 1.21V
■
Low Supply Current: 1.9mA
■
Low Shutdown Current: 20µA
■
Easily Synchronizable Up to 400kHz
■
Cycle-by-Cycle Current Limit
■
Reduced EMI Generation
■
Low Thermal Resistance SO-8 Package
■
Uses Small Low Value Inductors
The LT
®
1578 is a 200kHz monolithic buck mode switching
regulator. A 1.5A switch is included on the die along with
all the necessary oscillator, control and logic circuitry. The
topology is current mode for fast transient response and
good loop stability. The LT1578 is a modified version of the
LT1507 that has been optimized for noise sensitive appli-
cations. It will operate over a 4V to 15V input range.
In addition, the reference voltage has been lowered to al-
low the device to produce output voltages down to 1.2V.
Quiescent current has been reduced by a factor of two.
Switch on resistance has been reduced by 30%. Switch tran-
sition times have been slowed to reduce EMI generation.
The oscillator frequency has been reduced to 200kHz to
maintain high efficiency over a wide output current range.
The pinout has been changed to improve PC layout by al-
lowing the high current, high frequency switching circuitry
to be easily isolated from low current, noise sensitive con-
trol circuitry. The new SO-8 package includes a fused
ground lead that significantly reduces the thermal resistance
of the device to extend the ambient operating temperature
range. Standard surface mount external parts can be used
including the inductor and capacitors.
■
Portable Computers
■
Battery-Powered Systems
■
Battery Chargers
■
Distributed Power Systems
, LTC and LT are registered trademarks of Linear Technology Corporation.
LOAD CURRENT (A)
0
EFFICIENCY (%)
90
85
80
75
70
65
60
55
50
0.25
0.50 0.75 1.00
1578 TA02
1.25 1.50
V
OUT
= 3.3V
V
IN
= 5V
L = 25µH
DESCRIPTIO
U
FEATURES
APPLICATIO S
U
BOOST
LT1578
V
IN
SHDN
OUTPUT**
3.3V, 1.25A
* RIPPLE CURRENT RATING ≥ I
OUT
/2
** INCREASE L1 TO 30µH FOR LOAD
CURRENTS ABOVE 0.6A AND TO
60µH ABOVE 1A
SEE APPLICATIONS INFORMATION
INPUT
5V TO 15V
1578 TA01
C2
0.33µF
C
C
100pF
D1
1N5818
C1
100µF, 10V
SOLID
TANTALUM
C3*
10µF TO
50µF
OPEN = ON
D2
1N914
L1**
15µH
V
SW
FB
GND
V
C
+
+
R2
4.99k
R1
8.66k
TYPICAL APPLICATION
U
2
LT1578/LT1578-2.5
PARAMETER CONDITIONS MIN TYP MAX UNITS
Feedback Voltage 1.195 1.21 1.225 V
All Conditions ● 1.18 1.24 V
Sense Voltage (Fixed 2.5) 2.46 2.5 2.54 V
All Conditions ● 2.44 2.56 V
Sense Pin Resistance 5.7 9.5 13.7 kΩ
Reference Voltage Line Regulation 4.3V ≤ V
IN
≤ 15V ● 0.01 0.03 %/V
Feedback Input Bias Current ● 0.5 2 µA
Error Amplifier Voltage Gain (Notes 2, 10) 200 400
Error Amplifier Transconductance (Note 10) ∆I (V
C
) = ±10µA 800 1050 1300 µMho
● 400 1700 µMho
V
C
Pin to Switch Current Transconductance 1.5 A/V
Error Amplifier Source Current V
FB
= 1.1V ● 40 110 190 µA
Error Amplifier Sink Current V
FB
= 1.4V ● 50 130 200 µA
V
C
Pin Switching Threshold Duty Cycle = 0 0.8 V
V
C
Pin High Clamp 2.1 V
Switch Current Limit V
C
Open, V
FB
= 1.1V, DC ≤ 50% ● 1.5 2 3.5 A
Slope Compensation (Note 8) DC = 80% 0.3 A
Switch On Resistance (Note 7) I
SW
= 1.5A 0.2 0.35 Ω
● 0.45 Ω
Maximum Switch Duty Cycle V
FB
= 1.1V 90 94 %
● 86 94 %
Minimum Switch Duty Cycle (Note 9) 8%
Switch Frequency V
C
Set to Give 50% Duty Cycle 180 200 220 kHz
● 160 240 kHz
Switch Frequency Line Regulation 4.3V
≤ V
IN
≤ 15V ● 0 0.15 %/V
Frequency Shifting Threshold on FB Pin ∆f = 10kHz ● 0.4 0.74 1.0 V
Minimum Input Voltage (Note 3) ● 4.0 4.3 V
Minimum Boost Voltage (Note 4) I
SW
≤ 1.5A ● 2.3 3.0 V
ABSOLUTE MAXIMUM RATINGS
W
WW
U
PACKAGE/ORDER INFORMATION
W
U
U
(Note 1)
Input Voltage .......................................................... 16V
BOOST Pin Above Input Voltage ............................. 10V
SHDN Pin Voltage..................................................... 7V
SENSE Pin Voltage .................................................... 4V
FB Pin Voltage (Adjustable Part)............................ 3.5V
FB Pin Current (Adjustable Part)............................ 1mA
SYNC Pin Voltage ..................................................... 7V
Operating Junction Temperature Range
LT1578C............................................... 0°C to 125° C
LT1578I ........................................... –40°C to 125°C
Storage Temperature Range ................ –65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
The ● denotes specifications which apply over the full operating tempera-
ture range, otherwise specifications are at T
J
= 25°C. V
IN
= 5V, V
C
= 1.5V, Boost = V
IN
+ 5V, switch open, unless otherwise noted.
ELECTRICAL CHARACTERISTICS
Consult factory for Military grade parts.
ORDER PART
NUMBER
LT1578CS8
LT1578IS8
LT1578CS8-2.5
LT1578IS8-2.5
S8 PART MARKING
1578
1578I
1
2
3
4
8
7
6
5
TOP VIEW
S8 PACKAGE
8-LEAD PLASTIC SO
V
SW
V
IN
BOOST
GND
SHDN
FB/SENSE
V
C
SYNC
θ
JA
=80°C/W WITH FUSED GROUND PIN
CONNECTED TO GROUND PLANE OR
LARGE LANDS
157825
578I25
3
LT1578/LT1578-2.5
PARAMETER CONDITIONS MIN TYP MAX UNITS
Boost Current (Note 5) I
SW
= 0.5A ● 918 mA
I
SW
= 1.5A ● 27 50 mA
V
IN
Supply Current (Note 6) ● 1.9 2.7 mA
Shutdown Supply Current V
SHDN
= 0V, V
IN
≤ 15V, V
SW
= 0V, V
C
Open 20 50 µA
● 75 µA
Lockout Threshold V
C
Open ● 2.34 2.42 2.50 V
Shutdown Thresholds V
C
Open Device Shutting Down ● 0.13 0.37 0.60 V
Device Starting Up ● 0.25 0.45 0.7 V
Synchronization Threshold 1.5 2.2 V
Synchronizing Range 250 400 kHz
SYNC Pin Input Resistance 40 kΩ
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: Gain is measured with a V
C
swing equal to 200mV above the
switching threshold level to 200mV below the upper clamp level.
Note 3: Minimum input voltage is not measured directly, but is guaranteed
by other tests. It is defined as the voltage where internal bias lines are still
regulated so that the reference voltage and oscillator frequency remain
constant. Actual minimum input voltage to maintain a regulated output will
depend on output voltage and load current. See Applications Information.
Note 4: This is the minimum voltage across the boost capacitor needed to
guarantee full saturation of the internal power switch.
Note 5: Boost current is the current flowing into the boost pin with the pin
held 5V above input voltage. It flows only during switch on time.
Note 6: Input supply current is the bias current drawn by the input pin
with switching disabled.
Note 7: Switch on resistance is calculated by dividing V
IN
to V
SW
voltage
by the forced current (1.5A). See Typical Performance Characteristics for
the graph of switch voltage at other currents.
Note 8: Slope compensation is the current subtracted from the switch
current limit at 80% duty cycle. See Maximum Output Load Current in the
Applications Information section for further details.
Note 9: Minimum on-time is 400ns typical. For a 200kHz operating
frequency this means the minimum duty cycle is 8%. In frequency
foldback mode, the effective duty cycle will be less than 8%.
Note 10: Transconductance and voltage gain refer to the internal amplifier
exclusive of the voltage divider. To calculate gain and transconductance
referred to the sense pin on the fixed voltage parts, divide values shown by
the ratio 2.5/1.21.
TYPICAL PERFORMANCE CHARACTERISTICS
UW
Switch Voltage Drop
JUNCTION TEMPERATURE (°C)
–50
1.23
1.22
1.21
1.20
1.19
100
1576 G03
–25 0 25 50 75 125
FEEDBACK VOLTAGE (V)
SWITCH CURRENT (A)
0
SWITCH VOLTAGE (V)
0.5
0.4
0.3
0.2
0.1
0
0.25
0.50 0.75 1.00
1576 G01
1.25 1.50
125°C
–20°C
25°C
Feedback Pin VoltageSwitch Peak Current Limit
DUTY CYCLE (%)
0
SWITCH PEAK CURRENT (A)
2.5
2.0
1.5
1.0
0.5
0
80
1576 G02
20
40
60
100
TYPICAL
MINIMUM
The ● denotes specifications which apply over the full operating tempera-
ture range, otherwise specifications are at T
J
= 25°C. V
IN
= 5V, V
C
= 1.5V, Boost = V
IN
+ 5V, switch open, unless otherwise noted.
ELECTRICAL CHARACTERISTICS
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LT1578IS8-2.5#PBF

Mfr. #:
Buy LT1578IS8-2.5#PBF
Manufacturer:
Analog Devices / Linear Technology
Description:
Switching Voltage Regulators 1.5A, 200kHz Buck Sw Reg
Lifecycle:
New from this manufacturer.
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