LT1507
W
U
TYPICAL PERFORMANCE CHARACTERISTICS
Maximum Load Current
Maximum Load Current
at VOUT = 5V
at VOUT = 3.3V
Current Limit Foldback
2.5
2.0
1.5
1.0
0.5
0
1.50
1.25
1.50
1.25
V
OUT
= 3.3V
L = 20µH
L = 10µH
FOLDBACK
*POSSIBLE
UNDESIRED
CHARACTERISTICS
L = 10µH
L = 5µH
STABLE POINT
FOR CURRENT
SOURCE LOAD
CURRENT
SOURCE LOAD
1.00
0.75
1.00
0.75
L = 5µH
L = 3µH
0.50
0.25
0
0.50
0.25
0
L = 2µH
MOS LOAD
RESISTOR LOAD
0
20
40
60
80
100
4
6
8
10
12
14
0
3
6
9
12
15
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
OUTPUT VOLTAGE (%)
LT1507 • TPC13
LT1507 • TPC14
LT1507 • TPC15
*SEE "MORE THAN JUST VOLTAGE FEEDBACK"
IN APPLICATIONS INFORMATION SECTION
Inductor Core Loss for 3.3V Output
Boost Pin Current
Switch Voltage Drop
0.8
0.6
0.4
0.2
0
12
10
8
1.0
0.1
V
V
OUT
= 3.3V
OUT
IN
T
= 25°C
T = 25°C
J
J
= 5V
I
= 1A
TYPE 52 POWDERED IRON
Kool Mµ®
6
0.01
4
PERMALLOY
Metglas®
µ = 125
2
0
0.001
0
0.25 0.50 0.75 1.00 1.25 1.50
SWITCH CURRENT (A)
0
0.25
0.50
0.75
1.00
1.25
1
2
4
6
8
10
SWITCH CURRENT (A)
INDUCTANCE (µH)
LT1507 • TPC17
LT1507 • TPC18
LT1507 • TPC16
CORE LOSS IS INDEPENDENT OF LOAD CURRENT
UNTIL LOAD CURRENT FALLS LOW ENOUGH
FOR CIRCUIT TO GO INTO DISCONTINUOUS MODE
Kool Mµ is a registered trademark of Magnetics, Incorporated.
Metglas is a registered trademark of AlliedSignal Incorporated.
U
U
U
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,
butwithamuchsmallerdiearea.Efficiencyimprovesfrom
70% forconventionalbipolardesignstogreater than 85%
for these new parts.
VIN (Pin 2): Input Pin. The LT1507 is designed to operate
withaninputvoltagebetween4.5Vand15V.Undercertain
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
5
Linear [ Linear ]
