LTC1771I Linear Technology, LTC1771I Datasheet - Page 3

• Manufacturer Part Number: LTC1771I
• Description: Low Quiescent Current High Efficiency Step-Down DC/DC Controller
• Manufacturer: Linear Technology

PI FU CTIO S
RUN/SS (Pin 1): The voltage level on this pin controls
shutdown/run mode (ground = shutdown, open/high =
run). Connecting an external capacitor to this pin provides
soft-start.
I
current comparator threshold increases with this control
voltage. Nominal voltage range for this pin is 0V to 3V.
V
to Internal 1.23V Reference. An external resistive divider
across the output is returned to this pin.
GND (Pin 4): Ground Pin.
SYMBOL
V
I
PGATE t
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: T
dissipation P
Note 3: The LTC1771E is guaranteed to meet performance specifications
from 0 C to 70 C. Specifications over the – 40 C to 85 C operating
temperature range are assured by design, characterization and correlation
with statistical process controls. The LTC1771I is guaranteed and tested
over the – 40 C to 85 C operating temperature range.
ELECTRICAL CHARACTERISTICS
The
V
RUN
TH
RUN/SS
FB
IN
LTC1771S8: T
LTC1771MS8: T
U
= 10V, V
(Pin 2): Error Amplifier Compensation Point. The
(Pin 3): Feedback of Output Voltage for Comparison
denotes specifications which apply over the full operating temperature range, otherwise specifications are T A = 25 C.
r
, t
J
is calculated from the ambient temperature T
f
D
U
RUN
according to the following formulas:
PARAMETER
RUN/SS Pin Threshold
Source Current
PGATE Transition Time (Note 7)
J
= open unless otherwise specified.
= T
Rise Time
Fall Time
J
= T
A
+ (P
A
+ (P
U
D
)(110 C/W)
D
)(150 C/W)
A
and power
CONDITIONS
V
V
C
C
RUN/SS
RUN
LOAD
LOAD
= 0V, V
= 2000pF
= 2000pF
Rising
IN
= 2.8V to 18V
Note 4: Dynamic supply current is higher due to the gate charge being
delivered at the switching frequency. See Applications Information.
Note 5: The LTC1771 is tested in a feedback loop that servos V
balance point for the error amplifier (V
Note 6: No-load supply current consists of sleep mode current (9 A
typical) plus a small switching component necessary to overcome
Schottky diode leakage and feedback resistor current.
Note 7: t
PGATE (Pin 5): High Current Gate Driver for External
P-Channel MOSFET Switch. Voltage swing is from ground
to V
V
SENSE (Pin 7): Current Sense Input for Monitoring Switch
Current. Maximum switch current and Burst Mode
threshold is programmed with an external resistor be-
tween SENSE and V
MODE (Pin 8): Burst Mode Enable/Disable Pin. Connect-
ing this pin to V
operation, while connecting this pin to ground disables
Burst Mode operation. Do not leave floating.
IN
(Pin 6): Main Input Voltage Supply Pin.
IN
.
r
and t
f
measured at 10% to 90% levels.
IN
IN
(or above 2V) enables Burst Mode
.
MIN
0.5
0.3
ITH
= 1.23V).
TYP
1.0
80
90
1
LTC1771
MAX
2
3
FB
to the
UNITS
3
ns
ns
V
A