LT1959CR#TR Linear Technology, LT1959CR#TR Datasheet - Page 22

• Manufacturer Part Number: LT1959CR#TR
• Description: IC REG SW 4.5A 500KHZ STPDWN 7DD
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LT1959CR#TR

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 1.21 ~ 38 V
• Current - Output: 4.5A
• Frequency - Switching: 500kHz
• Voltage - Input: 4.3 ~ 15 V
• Operating Temperature: 0°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: D²Pak, TO-263 (7 leads + tab)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -

LT1959
APPLICATIONS
converters 120 out of phase with each other reduces
input and output ripple currents. This reduces the ripple
rating, size and cost of filter capacitors.
Current Sharing/Split Input Supplies
Current sharing is accomplished by joining the V
a common compensation capacitor. The output of the
error amplifier is a gm stage, so any number of devices can
be connected together. The effective gm of the composite
error amplifier is the multiple of the individual devices. In
Figure 15, the compensation capacitor C4 has been
increased by 3. Tolerances in the reference voltages
result in small offset currents to flow between the V
The overall effect is that the loop regulates the output at a
voltage between the minimum and maximum reference of
the devices used. Switch current matching between
devices will be typically better than 300mA. The negative
temperature coefficient of the V
ductance prevents current hogging.
A common V
same switch current, not duty cycle. Each device operates
at the duty cycle defined by its respective input voltage. In
Figure 15, the input could be split and each device oper-
ated at a different voltage. The common V
loading is shared between inputs.
22
4.3V TO 15V
INPUT
+
C
V
C
voltage forces each LT1959 to operate at the
L1A
6.8 H
SYNC SW GND
C3A
10 F
25V
D1A
U
LT1959
1.8MHz
330nF
INFORMATION
C2A
10V
U
V
D2A
IN
C
BOOST FB
to switch current transcon-
W
3-BIT RING
COUNTER
Figure 15. Current Sharing 12A Supply
+
V
C
L1B
6.8 H
C
SYNC SW GND
U
C3B
10 F
25V
D1B
C
C1, C3: MARCON THCS50E1E106Z
D1: ROHM RB051L-40
D2: 1N914
L1: DO3316P-682
ensures
pins to
C
pins.
LT1959
330nF
C2B
10V
V
D2B
IN
Synchronized Ripple Currents
A ring counter generates three synchronization signals at
600kHz, 33% duty cycle phased 120 apart. The sync
input will operate over a wide range of duty cycles, so no
further pulse conditioning is needed. Each device’s maxi-
mum input ripple current is a 4A square wave at 600kHz.
When synchronously added together, the ripple remains
at 4A but frequency increases to 1.8MHz. Likewise, the
output ripple current is a 1.8MHz triangular waveform,
with maximum amplitude of 350mA at 5V V
ingly, at 7.6V and 15V V
ripple current cancels completely. To reduce board space
and ripple voltage, C1 and C3 are ceramic capacitors. Loop
compensation C4 must be adjusted when using ceramic
output capacitors due to the lack of effective series resis-
tance. The typical tantalum compensation of 1.5nF is
increased to 22nF ( 3) for the ceramic output capacitor.
If synchronization is not used and the internal oscillators
free run, the circuit will operate correctly, but ripple
cancellation will not occur. Input and output capacitors
must be ripple rated for the total output current.
BOOST FB
+
C4
68nF
25V
+
V
C
L1C
6.8 H
SYNC SW GND
C3C
10 F
25V
D1C
IN
LT1959
, the theoretical summed output
330nF
C2C
10V
V
D2C
IN
BOOST FB
1959 F15
R1
2.67k
1%
R2
2.49k
1%
IN
. Interest-
+
C1
10 F
25V
2.5V
12A