LT1507
TYPICAL PERFORMANCE CHARACTERISTICS
Current Limit Foldback
2.5
*POSSIBLE
UNDESIRED
STABLE POINT
FOR CURRENT
SOURCE LOAD
FOLDBACK
CHARACTERISTICS
CURRENT
SOURCE LOAD
1.50
V
OUT
= 3.3V
1.25
L = 10µH
1.00
0.75
L = 3µH
0.50
0.5
MOS LOAD
0.25
RESISTOR LOAD
0
0
20
60
80
40
OUTPUT VOLTAGE (%)
100
0
4
6
8
10
INPUT VOLTAGE (V)
12
14
0
0
3
6
9
INPUT VOLTAGE (V)
12
15
L = 2µH
0.25
1.25
L = 10µH
1.00
L = 5µH
0.75
0.50
2.0
OUTPUT CURRENT (A)
CURRENT (A)
1.5
L = 5µH
1.0
LT1507 • TPC13
LT1507 • TPC14
CURRENT (A)
*SEE "MORE THAN JUST VOLTAGE FEEDBACK"
IN APPLICATIONS INFORMATION SECTION
Boost Pin Current
12
T
J
= 25°C
10
BOOST PIN CURRENT (mA)
CORE LOSS (W)
8
6
4
2
0
0.1
TYPE 52 POWDERED IRON
Kool Mµ
®
SWITCH VOLTAGE (V)
0
0.25
0.50
0.75
1.00
SWITCH CURRENT (A)
Kool Mµ is a registered trademark of Magnetics, Incorporated.
Metglas is a registered trademark of AlliedSignal Incorporated.
PIN FUNCTIONS
BOOST (Pin 1):
The BOOST pin is used to provide a drive
voltage, higher than the input voltage, to the internal
bipolar NPN power switch. Without this added voltage the
typical switch voltage loss would be about 1.5V. The
additional boost voltage allows the switch to saturate and
voltage loss approximates that of a 0.3Ω FET structure,
but with a much smaller die area. Efficiency improves from
70% for conventional bipolar designs to greater than 85%
for these new parts.
V
IN
(Pin 2):
Input Pin. The LT1507 is designed to operate
with an input voltage between 4.5V and 15V. Under certain
conditions, input voltage may be reduced down to 4V.
Actual minimum operating voltage will always be higher
than the output voltage. It may be limited by switch
U W
LT1507 • TPC16
Maximum Load Current
at V
OUT
= 3.3V
1.50
Maximum Load Current
at V
OUT
= 5V
L = 20µH
LT1507 • TPC15
Inductor Core Loss for 3.3V Output
1.0
V
OUT
= 3.3V
V
IN
= 5V
I
OUT
= 1A
0.6
0.8
Switch Voltage Drop
T
J
= 25°C
0.4
0.01
PERMALLOY
µ
= 125
Metglas
®
0.2
1.25
0.001
1
2
4
INDUCTANCE (µH)
6
8
10
0
0
0.25
0.50 0.75 1.00 1.25
SWITCH CURRENT (A)
1.50
LT1507 • TPC17
LT1507 • TPC18
CORE LOSS IS INDEPENDENT OF LOAD CURRENT
UNTIL LOAD CURRENT FALLS LOW ENOUGH
FOR CIRCUIT TO GO INTO DISCONTINUOUS MODE
U
U
U
5
LINER [ LINEAR TECHNOLOGY ]
