Datasheet

LTC3523/LTC3523-2
5
3523fb
Normalized R
DS(ON)
vs
Temperature
Step-Up No-Load Input Current
vs V
IN
PIN FUNCTIONS
FB1 (Pin 1): Step-Up Converter Feedback Input to the Er-
ror Amplifi er. Connect resistor divider tap to this pin. The
output voltage can be adjusted from 1.8V to 5.25V by:
V
OUT(STEP-UP)
=+
⎛
⎝
⎜
⎞
⎠
⎟
12 1
1
2
.•V
R
R
See Block Diagram.
V
IN1
(Pin 2): Step-Up Converter Power Voltage Input. This
pin can be connected to a different supply than V
IN2
. This
pin must be connected to a valid supply voltage.
PGOOD1 (Pin 3): Step-Up Converter Power Good Com-
parator Output. This open-drain output is pulled low when
V
FB1
< –9% of its regulation voltage.
V
OUT
(Pin 4): Step-Up Converter Output Voltage Sense Input
and Drain of the Internal Synchronous Rectifi er MOSFET.
Driver bias is derived from V
OUT
. PCB trace length from
V
OUT
to the output fi lter capacitor(s) should be as short
and wide as possible.
Mode Transition Response
TEMPERATURE (°C)
–45
NORMALIZED R
DS(ON)
(Ω)
1.2
15
3523 G10
0.9
0.7
–25 –5 35
0.6
0.5
1.3
1.1
1.0
0.8
55 75
PMOS
NMOS
INPUT VOLTAGE (V)
1.5
0
INPUT CURRENT (μA)
50
150
200
250
500
350
2.5
3.5
4
3523 G11
100
400
450
300
2
3
4.5
5
V
OUT
= 5V
V
OUT
= 3.3V
V
OUT
= 2.8V
V
OUT_BST
50mV/DIV
V
OUT_BCK
20mV/DIV
MODE
2V/DIV
200μs/DIV
3523 G12
V
OUT1
= 3.3V
V
OUT2
= 1.2V
V
IN
= 2.4V
I
OUT1
= 20mA
I
OUT2
= 25mA
C
OUT1
= C
OUT2
= 10μF
L1 = L2 = 4.7μH
Maximum I
OUT
vs V
IN
for the
Step-Up Converter
Maximum I
OUT
vs V
IN
for the
Step-Down Converter
INPUT VOLTAGE (V)
1
0
MAXIMUM OUTPUT CURRENT (mA)
50
150
200
250
500
350
2
3
3523 G13
100
400
450
300
4
5
V
OUT
= 2.5V
V
OUT
= 3.3V
V
OUT
= 5V
INPUT VOLTAGE (V)
1
MAXIMUM OUTPUT CURRENT (mA)
250
300
350
5
3523 G14
200
150
0
2
3
4
1.5
2.5
3.5
4.5
100
50
450
400
V
OUT
= 2.5V
V
OUT
= 1.8V
V
OUT
= 1.2V
TYPICAL PERFORMANCE CHARACTERISTICS
(T
A
= 25°C unless otherwise noted)