LT1576IS8-5SYNC Linear Technology, LT1576IS8-5SYNC Datasheet - Page 24

• Manufacturer Part Number: LT1576IS8-5SYNC
• Description: IC REG SW 5V 1.5A STEPDOWN 8SOIC
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LT1576IS8-5SYNC

• 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: -40°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: -

LT1576/LT1576-5
APPLICATIONS
with large inductors. Output ripple voltage for the positive-
to-negative converter will be much higher than a buck
converter. Ripple current in the output capacitor will also
be much higher. The following equations can be used to
calculate operating conditions for the positive-to-negative
converter.
Maximum load current:
I
V
V
V
0.35 = Switch voltage drop at 1.5A
Example: with V
V
does not take into account that maximum rated switch
current (I
cycles above 50%. If duty cycle is expected to exceed 50%
(input voltage less than output voltage), use the actual I
value from the Electrical Characteristics table.
Operating duty cycle:
(This formula uses an average value for switch loss, so it
may be several percent in error.)
With the conditions above:
24
P
IN
OUT
F
F
I
= Maximum rated switch current
MAX
DC
DC
= Catch diode forward voltage
= 0.5V, I
= Minimum input voltage
= Output voltage
V
5 5 0 3 5 0 5
P
IN
.
I
) on the LT1576 is reduced slightly for duty
P
P
= 1.5A: I
V
0 3
5 0 5
2
OUT
.
IN(MIN)
V
V
OUT
OUT
U
V
.
V
IN
OUT
MAX
V
F
= 5.5V, V
INFORMATION
V
V
V
U
= 0.6A. Note that this equation
.
OUT
IN
IN
V
F
f L
51
0 35
.
%
OUT
W
V
V
OUT
OUT
= 5V, L = 30 H,
V
V
IN
U
F
0 35
.
P
This duty cycle is close enough to 50% that I
assumed to be 1.5A.
OUTPUT DIVIDER
If the adjustable part is used, the resistor connected to
V
calculated from:
INDUCTOR VALUE
Unlike buck converters, positive-to-negative converters
cannot use large inductor values to reduce output ripple
voltage. At 200kHz, values larger than 75 H make almost
no change in output ripple. The graph in Figure 16 shows
peak-to-peak output ripple voltage for a 5V to – 5V con-
verter versus inductor value. The criteria for choosing the
OUT
Figure 16. Ripple Voltage on Positive-to-Negative Converter
R
1
(R2) should be set to approximately 5k. R1 is
R V
2
150
120
90
60
30
OUT
0
1 21
0
1 21
15
DISCONTINUOUS
I
INDUCTOR SIZE ( H)
LOAD
CONTINUOUS
I
LOAD
30
= 0.1A
5V TO –5V CONVERTER
OUTPUT CAPACITOR’S
ESR = 0.1
> 0.38A
DISCONTINUOUS
I
45
LOAD
= 0.25A
60
1576 F16
75
P
can be