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LT1959IS8#PBF

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1
LT1959
DESCRIPTIO
U
FEATURES
APPLICATIO S
U
TYPICAL APPLICATION
U
4.5A, 500kHz Step-Down
Switching Regulator
■
Operates with Input as Low as 4V
■
Output Range Down to 1.21V
■
Constant 500kHz Switching Frequency
■
Uses All Surface Mount Components
■
Inductor Size Reduced to 1.8
µ
H
■
Saturating Switch Design: 0.07Ω
■
Shutdown Current: 15µA
■
Easily Synchronizable
■
Cycle-by-Cycle Current Limiting
■
4.5A Switch
■
Current Mode Control
The LT
®
1959 is a 500kHz monolithic buck mode switching
regulator functionally identical to the LT1506 but optimized
for lower output voltage applications. It will operate down
to 1.21V output compared to 2.42V for the LT1506. A 4.5A
switch is included on the die along with all the necessary
oscillator, control and logic circuitry. High switching fre-
quency allows a considerable reduction in the size of ex-
ternal components. The topology is current mode for fast
transient response and good loop stability.
A special high speed bipolar process and new design tech-
niques achieve high efficiency at high switching frequency.
Efficiency is maintained over a wide output current range
by keeping quiescent supply current to 3.8mA
and by uti-
lizing a supply boost
capacitor to saturate the power switch.
The LT1959 fits into standard 7-pin DD and fused lead
SO-8 packages. Full cycle-by-cycle short-circuit protection
and thermal shutdown are provided. Standard surface
mount external parts are used, including the inductor and
capacitors. There is the optional function of shutdown or
synchronization. A shutdown signal reduces supply current
to 15µA. Synchronization allows an external logic level sig-
nal to increase the internal oscillator from 580kHz to 1MHz.
■
Portable Computers
■
Battery-Powered Systems
■
Battery Chargers
■
Distributed Power
■
5V to 3.3V Conversion
■
5V to 2.5V Conversion
■
5V to 1.8V Conversion
, LTC and LT are registered trademarks of Linear Technology Corporation.
Efficiency vs Load Current
5V to 1.8V Down Converter
BOOST
LT1959
V
IN
OUTPUT
1.8V
4A
INPUT
5V
1959 TA01
C2
0.68µF
C
C
1.5nF
D1
MBRS330T3
C1
100µF, 10V
SOLID
TANTALUM
C3
10µF TO
50µF
CERAMIC
D2
1N914
L1
5µH
V
SW
FBSHDN
OPEN
OR
HIGH
= ON
GND
V
C
+
+
R2
2.49k
R1
1.21k
LOAD CURRENT (A)
0
EFFICIENCY (%)
90
85
80
75
70
2.0 2.5 3.0 3.5
1959 TA02
0.5 1.0 1.5 4.0
V
OUT
= 3.3V
V
IN
= 5V
L = 10µH
2
LT1959
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C, T
J
= 25°C, V
IN
= 5V, V
C
= 1.5V, Boost = V
IN
+ 5V, switch open, unless
otherwise noted.
ABSOLUTE MAXIMUM RATINGS
W
WW
U
Input Voltage .......................................................... 16V
BOOST Voltage ........................................................ 30V
BOOST Pin Above Input Voltage ............................. 15V
SHDN Pin Voltage..................................................... 7V
FB Pin Voltage ....................................................... 3.5V
FB Pin Current ....................................................... 1mA
SYNC Pin Voltage ..................................................... 7V
Operating Junction Temperature Range
LT1959C................................................ 0°C to 125°C
LT1959I ........................................... –40°C to 125°C
Storage Temperature Range ................ –65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
ELECTRICAL CHARACTERISTICS
PARAMETER CONDITIONS MIN TYP MAX UNITS
Feedback Voltage (Adjustable) All Conditions ● 1.19 1.21 1.23 V
Reference Voltage Line Regulation 4.3V ≤ V
IN
≤ 15V 0.01 0.03 %/V
Feedback Input Bias Current ● –0.5 0 0.5 µA
Error Amplifier Voltage Gain (Note 2) 200 400
Error Amplifier Transconductance ∆I (V
C
) = ±10µA 1500 2000 2700 µMho
● 1000 3100 µMho
V
C
Pin to Switch Current Transconductance 5.3 A/V
Error Amplifier Source Current V
FB
= 1.05V ● 140 225 320 µA
Error Amplifier Sink Current V
FB
= 1.35V ● 140 225 320 µA
V
C
Pin Switching Threshold Duty Cycle = 0 0.9 V
V
C
Pin High Clamp 2.1 V
Switch Current Limit V
C
Open, V
FB
= 1.05V, DC ≤ 50% ● 4.5 6 8.5 A
Slope Compensation DC = 80% 0.8 A
PACKAGE/ORDER INFORMATION
W
U
U
ORDER PART
NUMBER
ORDER PART
NUMBER
LT1959CR
LT1959IR
1959
1959I
S8 PART MARKING
LT1959CS8
LT1959IS8
(Note 1)
1
2
3
4
8
7
6
5
TOP VIEW
S8 PACKAGE
8-LEAD PLASTIC SO
V
IN
BOOST
GND**
V
SW
SYNC
SHDN
V
C
FB
R PACKAGE
7-LEAD PLASTIC DD
FRONT VIEW
FB
BOOST
V
IN
GND
V
SW
7
6
5
4
3
2
1
SHDN
V
C
TAB
IS
GND
**WITH (FUSED GND) GROUND PIN
CONNECTED TO GROUND PLANE OR
LARGE LANDS
T
JMAX
= 150°C, θ
JA
= 30°C/W
WITH PACKAGE SOLDERED TO 0.5 SQUARE INCH
COPPER AREA OVER BACKSIDE GROUND PLANE OR
INTERNAL POWER PLANE. θ
JA
CAN VARY FROM 20°C/W
TO >40°C/W DEPENDING ON MOUNTING TECHNIQUES
T
JMAX
= 150°C, θ
JA
= 80°C/W
3
LT1959
ELECTRICAL CHARACTERISTICS
PARAMETER CONDITIONS MIN TYP MAX UNITS
Switch On Resistance (Note 7) I
SW
= 4.5A 0.07 0.1 Ω
● 0.13 Ω
Maximum Switch Duty Cycle V
FB
= 1.05V 90 93 %
● 86 93 %
Switch Frequency V
C
Set to Give 50% Duty Cycle 460 500 540 kHz
● 440 560 kHz
Switch Frequency Line Regulation 4.3V
≤ V
IN
≤ 15V ● 0 0.15 %/V
Frequency Shifting Threshold on FB Pin ∆f = 10kHz ● 0.5 0.7 1.0 V
Minimum Input Voltage (Note 3) ● 4.0 4.3 V
Minimum Boost Voltage (Note 4) I
SW
≤ 4.5A ● 2.3 3.0 V
Boost Current (Note 5) I
SW
= 1A ● 20 35 mA
I
SW
= 4.5A ● 90 140 mA
Input Supply Current (Note 6) ● 3.8 5.4 mA
Shutdown Supply Current V
SHDN
= 0V, V
SW
= 0V, V
C
Open 15 50 µA
● 75 µA
Lockout Threshold V
C
Open ● 2.3 2.38 2.46 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 580 1000 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 (4.5A). See Typical Performance Characteristics for
the graph of switch voltage at other currents.
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C, T
J
= 25°C, V
IN
= 5V, V
C
= 1.5V, Boost = V
IN
+ 5V, switch open, unless
otherwise noted.
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LT1959IS8#PBF

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Buy LT1959IS8#PBF
Manufacturer:
Analog Devices / Linear Technology
Description:
Switching Voltage Regulators 4.5A, 500kHz Buck Sw Reg
Lifecycle:
New from this manufacturer.
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