lp55271tlx National Semiconductor Corporation, lp55271tlx Datasheet - Page 8

• Manufacturer Part Number: lp55271tlx
• Description: Tiny Led Driver For Camera Flash And 4 Leds With I2c Programmability, Connectivity Test And Audio Synchronization
• Manufacturer: National Semiconductor Corporation

www.national.com
Magnetic Boost DC/DC Converter
MAGNETIC BOOST DC/DC CONVERTER ELECTRICAL CHARACTERISTICS
Note 10: Specified currents are the worst case currents. If input voltage is larger or output voltage is smaller, current can be increased according to graph "Boost
Maximum Output Current".
BOOST STANDBY MODE
User can set the boost converter to STANDBY mode by
writing the register bit EN_BOOST low when there is no load
to avoid idle current consumption. When EN_BOOST is
written high, the converter starts in low current PWM (Pulse
Width Modulation) mode for 10 ms and then goes to normal
PWM mode.
BOOST CONTROL REGISTERS
User can control the boost output voltage and the switching
frequency according to the following tables.
Limits in standard typeface are for T
range (-30
3.6V, C
C
Symbol
I
V
RDS
f
t
t
I
LOAD
PWF
PULSE
STARTUP
CL_OUT
OUT
VDD2
Boost Output Voltage
ON
[3:0] Register
= 100 nF, L
IN
= 10 µF, C
o
0000
0001
1000
1001
0011
0111
1011
1111
C
<
Parameter
Load Current
(Note 10)
Output Voltage Accuracy
(FB pin)
Output Voltage
(FB Pin)
Switch ON Resistance
PWM Mode Switching
Frequency
Frequency Accuracy
Switch Pulse Minimum
Width
Startup Time
SW1 + SW2 current limit
T
A
1
<
= 4.7 µH. (Note 9)
OUT1
+85
o
= 10 µF, C
C). Unless otherwise noted, specifications apply to the LP55271 Block Diagram with: V
Boost Output Voltage (V)
4.60 default
J
OUT2
(Typical)
= 25
4.00
4.20
4.40
4.80
5.00
5.20
5.40
Conditions
3.2V ≤ V
V
3.2V ≤ V
V
active load off
3.0V ≤ V
active load off
V
V
RT = 82 kΩ
FREQ_SEL (bit) = 1
FREQ_SEL (bit) = 0
3.2V ≤ V
RT = 82 kΩ
no load
= 10 µF, C
o
OUT
OUT
IN
IN
C. Limits in boldface type apply over the operating ambient temperature
= 3.6V, I
>
= 5.0V
(target value) = 5.0V,
(5.0V + V
IN
IN
IN
DD1,2
VDDIO
≤ 4.5V
≤ 4.5V
≤ (5.0V+V
SW
≤ 5.0V
(Continued)
= 1.0A
SCHOTTKY
= 100 nF, C
8
SCHOTTKY
)
FREQ_SEL Bit
VREF
)
= 100 nF, C
0
1
Min
−5
−6
-9
VDDA
Typ
5.0
V
0.20
2.0
1.0
25
10
1.7
±
IN
3
- V
= 4.7 µF, C
SCHOTTKY
Boost Switching
1.0 MHz default
Frequency
(Typical)
2.0 MHz
VDD1
Max
670
+5
0.4
+6
+9
= 100 nF,
IN
Units
mA
%
V
Ω
MHz
%
ns
ms
A
=