Datasheet

5
LTC1159
LTC1159-3.3/LTC1159-5
PI FU CTIO S
U
UU
SENSE
+
: The (+) Input for the Current Comparator. A built-
in offset between the SENSE
+
and SENSE
–
pins, in conjunc-
tion with R
SENSE
, sets the current trip threshold.
N-Gate: High Current Drive for the Bottom N-Channel
MOSFET. The N-Gate pin swings from ground to V
CC
.
P-Gate: Level-Shifted Gate Drive Signal for the Top
P-Channel MOSFET. The voltage swing at the P-gate pin is
from V
IN
to V
IN
– V
CC
.
P-Drive: High Current Gate Drive for the Top P-Channel
MOSFET. The P-drive pin(s) swing(s) from V
CC
to ground.
CAP: Charge Compensation Pin. A capacitor to V
CC
pro-
vides charge required by the P-gate level-shift capacitor
during supply transitions. The charge compensation ca-
pacitor must be larger than the gate drive capacitor .
SHDN1: This pin shuts down the control circuitry only (V
CC
is not affected). Taking SHDN1 pin high turns off the
control circuitry and holds both MOSFETs off. This pin
must be at ground potential for normal operation.
SHDN2: Master Shutdown Pin. Taking SHDN2 high shuts
down V
CC
and all control circuitry.
V
IN
: Main Supply Input Pin.
SGND: Small-Signal Ground. Must be routed separately
from other grounds to the (–) terminal of C
OUT
.
PGND: Driver Power Grounds. Connect to source of N-
channel MOSFET and the (–) terminal of C
IN
.
V
CC
: Outputs of internal 4.5V linear regulator, EXTV
CC
switch, and supply inputs for driver and control circuits.
The driver and control circuits are powered from the higher
of the 4.5V regulator or EXTV
CC
voltage. Must be closely
decoupled to power ground.
C
T
: External capacitor C
T
from this pin to ground sets the
operating frequency. (The frequency is also dependent on
the ratio V
OUT
/V
IN
.)
I
TH
: Gain Amplifier Decoupling Point. The current com-
parator threshold increases with the I
TH
pin voltage.
V
FB
: For the LTC1159 adjustable version, the V
FB
pin
receives the feedback voltage from an external resistive
divider used to set the output voltage.
SENSE
–
: Connects to internal resistive divider which sets
the output voltage in fixed output versions. The SENSE
–
pin
is also the (–) input of the current comparator.
EXTV
CC
Switch Drop Current Sense Threshold Voltage
Off-Time vs V
OUT
SWITCH CURRENT (mA)
0
0
EXTV
CC
– V
CC
(mV)
100
200
300
400
500
600
5101520
LTC1159 • TPC07
OUTPUT VOLTAGE (V)
1
OFF-TIME (µs)
40
50
60
5
LTC1159 • TPC08
30
20
0
2
34
10
80
70
0
LTC1159-5
LTC1159-3.3
TEMPERATURE (°C)
20
SENSE VOLTAGE (mV)
80
100
120
100
LTC1159 • TPC09
60
40
0
40
60 80
20
160
140
0
MAXIMUM
THRESHOLD
MINIMUM
THRESHOLD
TYPICAL PERFOR A CE CHARACTERISTICS
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