LT1578 Linear Technology, LT1578 Datasheet - Page 3

• Manufacturer Part Number: LT1578
• Description: 1.5A/ 200kHz Step-Down Switching Regulator
• Manufacturer: Linear Technology

ELECTRICAL CHARACTERISTICS
ture range, otherwise specifications are at T
PARAMETER
Boost Current (Note 5)
V
Shutdown Supply Current
Lockout Threshold
Shutdown Thresholds
Synchronization Threshold
Synchronizing Range
SYNC Pin Input Resistance
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: Gain is measured with a V
switching threshold level to 200mV below the upper clamp level.
Note 3: Minimum input voltage is not measured directly, but is guaranteed
by other tests. It is defined as the voltage where internal bias lines are still
regulated so that the reference voltage and oscillator frequency remain
constant. Actual minimum input voltage to maintain a regulated output will
depend on output voltage and load current. See Applications Information.
Note 4: This is the minimum voltage across the boost capacitor needed to
guarantee full saturation of the internal power switch.
Note 5: Boost current is the current flowing into the boost pin with the pin
held 5V above input voltage. It flows only during switch on time.
Note 6: Input supply current is the bias current drawn by the input pin
with switching disabled.
TYPICAL PERFORMANCE CHARACTERISTICS
IN
0.5
0.4
0.3
0.2
0.1
Supply Current (Note 6)
0
Switch Voltage Drop
0
0.25
SWITCH CURRENT (A)
0.50
0.75
25 C
1.00
–20 C
C
swing equal to 200mV above the
125 C
W
1.25
1576 G01
1.50
U
CONDITIONS
I
I
V
V
V
Device Starting Up
SW
SW
SHDN
C
C
Open
Open Device Shutting Down
J
= 0.5A
= 1.5A
= 25 C. V
= 0V, V
2.5
2.0
1.5
1.0
0.5
0
Switch Peak Current Limit
0
IN
IN
15V, V
= 5V, V
20
The
SW
DUTY CYCLE (%)
MINIMUM
TYPICAL
C
denotes specifications which apply over the full operating tempera-
40
= 0V, V
= 1.5V, Boost = V
Note 7: Switch on resistance is calculated by dividing V
by the forced current (1.5A). See Typical Performance Characteristics for
the graph of switch voltage at other currents.
Note 8: Slope compensation is the current subtracted from the switch
current limit at 80% duty cycle. See Maximum Output Load Current in the
Applications Information section for further details.
Note 9: Minimum on-time is 400ns typical. For a 200kHz operating
frequency this means the minimum duty cycle is 8%. In frequency
foldback mode, the effective duty cycle will be less than 8%.
Note 10: Transconductance and voltage gain refer to the internal amplifier
exclusive of the voltage divider. To calculate gain and transconductance
referred to the sense pin on the fixed voltage parts, divide values shown by
the ratio 2.5/1.21.
C
60
Open
80
1576 G02
IN
100
+ 5V, switch open, unless otherwise noted.
1.23
1.22
1.21
1.20
1.19
LT1578/LT1578-2.5
–50
Feedback Pin Voltage
–25
MIN
2.34
0.13
0.25
250
JUNCTION TEMPERATURE ( C)
0
2.42
0.37
0.45
TYP
1.9
1.5
27
20
40
9
25
IN
50
MAX
2.50
0.60
400
2.7
0.7
2.2
18
50
50
75
to V
75
SW
voltage
100
UNITS
1576 G03
3
kHz
mA
mA
mA
125
k
A
A
V
V
V
V