Datasheet

3
LTC1649
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a part may be impaired.
Note 2: All currents into device pins are positive; all currents out of device
pins are negative. All voltages are referenced to ground unless otherwise
specified.
Note 3: Maximum Duty Cycle limitations will limit the output voltage
obtainable at very low supply voltages.
Note 4: Supply current at P
VCC1
and P
VCC2
is dominated by the current
needed to charge and discharge the external MOSFET gates. This current
will vary with the operating voltage and the external MOSFETs used.
Note 5: Under normal operating conditions, the charge pump will skip
cycles to maintain regulation and the apparent frequency will be lower than
700kHz.
Note 6: The I
LIM
amplifier can sink but not source current. Under normal
(not current limited) operation, the I
LIM
output current will be zero.
Note 7: Driver rise and fall times are measured from 10% to 90%.
TYPICAL PERFOR A CE CHARACTERISTICS
UW
TEMPERATURE (°C)
–40
210
220
240
20 60
1649 G02
200
190
–20 0
40 80 100
180
170
230
OSCILLATOR FREQUENCY (kHz)
V
CC
= 5V
Oscillator Frequency
vs Temperature
TEMPERATURE (°C)
–40
12.5
13.0
14.0
20 60
1649 G01
12.0
11.5
–20 0
40 80 100
11.0
10.5
13.5
I
MAX
CURRENT (µA)
V
CC
= 5V
I
MAX
Pin Current vs Temperature
TEMPERATURE (°C)
–40
70
DUTY CYCLE (%)
75
85
90
95
0
40
60
1649 G03
80
–20 20
80
100
100
V
COMP
= V
CC
V
FB
= 1.265V
V
CC
= 5V
Maximum Duty Cycle
vs Temperature
Error Amplifier Transconductance
vs Temperature
TEMPERATURE (°C)
–40
350
TRANSCONDUCTANCE (µmho)
400
500
550
600
850
700
0
40
60 100
1649 G04
450
750
800
650
–20 20
80
g
m
=
∆I
COMP
∆V
FB
V
CC
= 5V
Output Voltage vs Load Current
with Current Limit
LOAD CURRENT (A)
0
OUTPUT VOLTAGE (V)
1.5
2.0
2.5
6
10
1649 G07
1.0
0.5
0
24 8
3.0
3.5
4.0
12
T
A
= 25°C
V
CC
= 5V
FIGURE 1
R
IMAX
= 16k R
IMAX
= 33k
Load Regulation
LOAD CURRENT (A)
0
–1.0
∆V
OUT
(mV)
–0.8
–0.4
–0.2
0
0.4
1
5
7
1649 G06
–0.6
0.2
4
9
10
2
3
68
T
A
= 25°C
V
OUT
= 3.3V
V
CC
= 5V
FIGURE 1
ELECTRICAL CHARACTERISTICS