LT1959IS8#TRPBF Linear Technology, LT1959IS8#TRPBF Datasheet - Page 14

• Manufacturer Part Number: LT1959IS8#TRPBF
• Description: IC SW REG STEPDN 500KHZ 8SOIC
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LT1959IS8#TRPBF

• 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: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -

LT1959
APPLICATIONS
Keep the connections from the resistors to the shutdown
pin short and make sure that interplane or surface capaci-
tance to the switching nodes are minimized. If high
resistor values are used, the shutdown pin should be
bypassed with a 1000pF capacitor to prevent coupling
problems from the switch node. If hysteresis is desired in
the undervoltage lockout point, a resistor R
added to the output node. Resistor values can be calcu-
lated from:
25k suggested for R
V
Example: output voltage is 5V, switching is to stop if input
voltage drops below 6V and should not restart unless
input rises back to 7.5V. V is therefore 1.5V and V
Let R
14
IN
V = Hysteresis in input voltage level
R
R
= Input voltage at which switching stops as input
HI
FB
LO
voltage descends to trip level
= 25k.
R
R
LO IN
HI
V
V
INPUT
OUT
2 38
2 38
U
LO
C1
V
INFORMATION
R
U
V V
2 3 5
R
R
LO
HI
OUT
A
W
IN
SHDN
LT1959
1
V
Figure 4. Undervoltage Lockout
FB
3.5 A
U
IN
can be
2.38V
= 6V.
0.4V
GND
R
FB
SWITCH NODE CONSIDERATIONS
For maximum efficiency, switch rise and fall times are
made as short as possible. To prevent radiation and high
frequency resonance problems, proper layout of the com-
ponents connected to the switch node is essential. B field
(magnetic) radiation is minimized by keeping catch diode,
switch pin, and input bypass capacitor leads as short as
possible. E field radiation is kept low by minimizing the
length and area of all traces connected to the switch pin
and BOOST pin. A ground plane should always be used
under the switcher circuitry to prevent interplane cou-
pling. A suggested layout for the critical components is
shown in Figure 5. Note that the feedback resistors and
compensation components are kept as far as possible
R
R
HI
FB
25 5 2
25 6 2 38 1 5 5 1
48 5 1 5
2 29
k
k
k
.
LOCKOUT
TOTAL
SHUTDOWN
2 38 25 3 5
.
/ .
.
.
V
48
SW
160
k
. /
k
k
.
A
+
1 5
.
OUTPUT
1959 F04