Datasheet

6
LTC1266
LTC1266 -3.3/LTC1266 -5
TDRIVE (Pin 1): High Current Drive for Topside MOSFET.
This MOSFET can be either P-channel or N-channel, user
selectable by Pin 3. Voltage swing at this pin is from PWR
V
IN
to ground.
PWR V
IN
(Pin 2): Power Suppy for Drive Signals. Must be
closely decoupled to power ground (Pin 15).
PINV (Pin 3): Phase Invert. Sets the phase of the topside
driver to drive either a P-channel or an N-channel MOSFET
as follows:
P-channel: Pin 3 = 0V
N-channel: Pin 3 = PWR V
IN
BINH (Pin 4): Burst Mode Operation Inhibit. A CMOS logic
high on this pin will disable the Burst Mode operation
feature forcing continuous operation down to zero load.
V
IN
(Pin 5): Main Supply Pin.
C
T
(Pin 6): External Capacitor. C
T
from Pin 4 to ground sets
the operating frequency. The actual frequency is also
dependent on the input voltage.
I
TH
(Pin 7): Gain Amplifier Decoupling Point. The current
comparator threshold increases with the Pin 7 voltage.
SENSE
–
(Pin 8): Connects to internal resistive divider
which sets the output voltage in LTC1266-3.3 and
LTC1266-5 versions. Pin 8 is also the (–) input for the
current comparator.
SENSE
+
(Pin 9): The (+) Input to the Current Comparator.
A built-in offset between Pins 8 and 9 in conjunction with
R
SENSE
sets the current trip threshold.
V
FB
(Pin 10): For the LTC1266 adjustable version, Pin 10
serves as the feedback pin from an external resistive
divider used to set the output voltage. On LTC1266-3.3
and LTC1266-5 versions this pin is not used.
SHDN (Pin 11): When grounded, the LTC1266 series
operates normally. Pulling Pin 11 high holds both
MOSFETs off and puts the LTC1266 in micropower shut-
down mode. Requires CMOS logic signal with t
r
, t
f
< 1µs.
Should not be left floating.
SGND (Pin 12): Small-Signal Ground. Must be routed
separately from other grounds to the (–) terminal of C
OUT
.
LB
IN
(Pin 13): Input to the Low-Battery Comparator. This
input is compared to an internal 1.25V reference.
LB
OUT
(Pin 14): Open Drain Output of the Low-Battery
Comparator. This pin will sink current when Pin 13 is
below 1.25V.
PGND (Pin 15): Driver Power Ground. Connects to source
of N-channel MOSFET and the (–) terminal of C
IN
.
BDRIVE (Pin 16): High Current Drive for Bottom
N-Channel MOSFET. Voltage swing at Pin 16 is from
ground to PWR V
IN
.
UU
U
PI FU CTIO S
OUTPUT VOLTAGE (V)
01
OFF-TIME (µs)
40
60
5
1266 G10
20
0
2
34
100
80
LTC1266-3.3
LTC1266-5
V
SENSE
–
= V
OUT
(V
IN
– V
OUT
) VOLTAGE (V)
0
NORMALIZED FREQUENCY
2.5
3.0
12108
1266 G11
0.5
1.5
2.0
1.0
0
2
4
6
14
16
V
OUT
= 3.3V
0°C
70°C
25°C
TEMPERATURE (°C)
0
SENSE VOLTAGE (mV)
100
150
200
80
1266 G12
50
0
–50
20
40
60
100
MAX THRESHOLD
MIN THRESHOLD (Burst Mode
OPERATION INHIBIT)
MIN THRESHOLD (Burst Mode
OPERATION ENABLED)
Off-Time vs Output Voltage
Operating Frequency
vs (V
IN
– V
OUT
) Voltage Current Sense Threshold Voltage
TYPICAL PERFOR A CE CHARACTERISTICS
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