LT1956IGN#TR Linear Technology, LT1956IGN#TR Datasheet - Page 17

• Manufacturer Part Number: LT1956IGN#TR
• Description: IC SW REG STP-DWN HI VOLT 16SSOP
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LT1956IGN#TR

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 1.2 ~ 45 V
• Current - Output: 1.5A
• Frequency - Switching: 500kHz
• Voltage - Input: 5.5 ~ 60 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 16-SSOP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -
• Other names: LT1956IGNTR

APPLICATIO S I FOR ATIO
LAYOUT CONSIDERATIONS
As with all high frequency switchers, when considering
layout, care must be taken in order to achieve optimal
electrical, thermal and noise performance. For maximum
efficiency, switch rise and fall times are typically in the
nanosecond range. To prevent noise both radiated and
conducted, the high speed switching current path, shown
in Figure 5, must be kept as short as possible. This is
implemented in the suggested layout of Figure 6. Shorten-
ing this path will also reduce the parasitic trace inductance
of approximately 25nH/inch. At switch off, this parasitic
inductance produces a flyback spike across the LT1956
switch. When operating at higher currents and input
voltages, with poor layout, this spike can generate volt-
ages across the LT1956 that may exceed its absolute
maximum rating. A ground plane should always be used
under the switcher circuitry to prevent interplane coupling
and overall noise.
MINIMIZE LT1956
C3-D1 LOOP
U
GND
V
IN
U
GROUND PINS (4 CORNERS) FOR
GOOD THERMAL CONDUCTIVITY
PLACE FEEDTHROUGH AROUND
D1
C3
W
L1
GND
SW
V
BOOST
GND
C2
IN
U
LT1956
Figure 6. Suggested Layout
D2
BIAS
GND
GND
FB
V
C
SHDN
SYNC
The V
possible from the switch and boost nodes. The LT1956
pinout has been designed to aid in this. The ground for
these components should be separated from the switch
current path. Failure to do so will result in poor stability or
subharmonic like oscillation.
R1
C
FB
C1
C
GROUND PLANE
R
C
CONNECT TO
V
and FB components should be kept as far away as
C
C
IN
R2
C
F
Figure 5. High Speed Switching Path
KEEP FB AND V
AWAY FROM HIGH FREQUENCY,
HIGH CURRENT COMPONENTS
C3
V
GND
KELVIN SENSE
OUT
V
CIRCULATING
OUT
FREQUENCY
1956 F06
LT1956
HIGH
PATH
FOR THE FE PACKAGE,
SOLDER THE EXPOSED
PAD TO THE COPPER
GROUND PLANE
UNDERNEATH THE DEVICE
C
COMPONENTS
LT1956/LT1956-5
D1 C1
L1
LOAD
1956 F05
17
5V
1956f