LT1576CS8-5#TR Linear Technology, LT1576CS8-5#TR Datasheet - Page 13

• Manufacturer Part Number: LT1576CS8-5#TR
• Description: IC REG SW 5V 1.5A STEPDOWN 8SOIC
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LT1576CS8-5#TR

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 5V
• Current - Output: 1.5A
• Frequency - Switching: 200kHz
• Voltage - Input: 5 ~ 25 V
• Operating Temperature: 0°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -

APPLICATIONS
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
capacitors remain capacitive to beyond 300kHz and usu-
ally 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.
OUTPUT RIPPLE VOLTAGE
Figure 3 shows a typical output ripple voltage waveform
for the LT1576. 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:
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.
I
I
RIPPLE RMS
P
-P
dI
dt
V
V
L
OUT
IN
V
IN
V
0 29
IN
U
L f
V
V
OUT
INFORMATION
OUT
L f V
U
V
IN
IN
W
V
OUT
U
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
regulator input voltage. Average forward current in normal
operation can be calculated from:
I
I
200mA/DIV
200mA/DIV
V
V
P-P
D AVG
20mV/DIV
20mV/DIV
RIPPLE
RIPPLE
0 042 0 003 45
dt
dI
Figure 3. LT1576 Ripple Voltage Waveform
10 30 10
30 10
I
OUT
I
10
P-P
0 42
IN
V
=10V, V
IN
ESR
V
6
A
5 10 5
IN
0 1
V
0 33 10
6
OUT
mV
2 s/DIV
OUT
LT1576/LT1576-5
ESL
200 10
P-P
= 5V, L = 30 H, ESR = 0.1 ,
10 10
6
dI
dt
3
9
0 42
0 33 10
1576 F03
A
V
I
V
I
INDUCTOR
CURRENT
AT I
INDUCTOR
CURRENT
AT I
OUT
OUT
OUT
OUT
OUT
OUT
= 1A
13
= 50mA
AT
AT
= 50mA
= 1A
6