LT1376CS Linear Technology, LT1376CS Datasheet - Page 13

• Manufacturer Part Number: LT1376CS
• Description: IC SW REG 1.5A ADJ STP-DWN16SOIC
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LT1376CS

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 2.42 ~ 21.5 V
• Current - Output: 1.5A
• Frequency - Switching: 500kHz
• Voltage - Input: 5 ~ 25 V
• Operating Temperature: 0°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 16-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -

APPLICATIONS
discharge surges, such as when the regulator output is
dead shorted, do not harm the capacitors.
Unlike the input capacitor, RMS ripple current in the
output capacitor is normally low enough that ripple cur-
rent rating is not an issue. The current waveform is
triangular with a typical value of 200mA
to calculate this is:
Output Capacitor Ripple Current (RMS):
Ceramic Capacitors
Higher value, lower cost ceramic capacitors are now
becoming available in smaller case sizes. These are tempt-
ing for switching regulator use because of their very low
ESR. Unfortunately, the ESR is so low that it can cause
loop stability problems. Solid tantalum capacitor’s ESR
generates a loop “zero” at 5kHz to 50kHz that is instrumen-
tal in giving acceptable loop phase margin. Ceramic ca-
pacitors remain capacitive to beyond 300kHz and usually
resonate with their ESL before ESR becomes effective.
They are appropriate for input bypassing because of their
high ripple current ratings and tolerance of turn-on surges.
For further information on ceramic and other capacitor
types please refer to Design Note 95.
OUTPUT RIPPLE VOLTAGE
Figure 3 shows a typical output ripple voltage waveform
for the LT1376. Ripple voltage is determined by the high
frequency impedance of the output capacitor, and ripple
current through the inductor. Peak-to-peak ripple current
through the inductor into the output capacitor is:
For high frequency switchers, the sum of ripple current
slew rates may also be relevant and can be calculated
from:
I
I
RIPPLE RMS
P
-P
=
( )
( )
V
OUT
( )( )( )
V
=
IN
(
V
0 29
IN
.
U
L f
−
( )
V
V
OUT
( )( )( )
INFORMATION
OUT
L f V
U
)
(
V
IN
IN
−
W
V
OUT
RMS
)
. The formula
U
Peak-to-peak output ripple voltage is the sum of a triwave
created by peak-to-peak ripple current times ESR, and a
square wave created by parasitic inductance (ESL) and
ripple current slew rate. Capacitive reactance is assumed
to be small compared to ESR or ESL.
Example: with V
ESL = 10nH:
CATCH DIODE
The suggested catch diode (D1) is a 1N5818 Schottky, or
its Motorola equivalent, MBR130. It is rated at 1A average
forward current and 30V reverse voltage. Typical forward
voltage is 0.42V at 1A. The diode conducts current only
during switch off time. Peak reverse voltage is equal to
20mV/DIV
0.5A/DIV
I
Σ
V
Σ
V
=
P-P
RIPPLE
RIPPLE
0 05 0 01 60
dt
dt
dI
dI
Figure 3. LT1376 Ripple Voltage Waveform
.
=
=
=
( )
10 10 10
+
10 10
V
=
=
L
IN
( )( )
( )( )
•
.
I
⎛
⎝
10
0 5
P-P
.
IN
=
A
−
=10V, V
( )
•
ESR
6
5 10 5
=
0 1
(
mV
0.5µs/DIV
.
−
10
6
⎞
⎠
+
+ ⎛ ⎝
−
P-P
OUT
6
⎛
⎝
( )
500 10
ESL
10 10
)
= 5V, L = 10µH, ESR = 0.1Ω,
LT1375/LT1376
•
•
Σ
dI
dt
−
3
9
⎞
⎠
⎞
⎠
1375/76 F03
=
⎛
⎝
10
0 5
.
V
V
INDUCTOR CURRENT
AT I
6
INDUCTOR CURRENT
AT I
OUT
OUT
A
⎞
⎠
OUT
OUT
AT I
AT I
= 50mA
= 1A
OUT
OUT
13
= 1A
= 50mA
13756fd