LP3958 Datasheet, PDF (9/36 Pages) National Semiconductor (TI) – Lighting Management Unit with High Voltage Boost Converter

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LP3958
SNVS423C – JANUARY 2006 – REVISED MARCH 2013
1 MHz clock
Duty control
V_IN
SW
UVCOMP
-
2V
+
OVPCOMP
+
-
-
+
ERRORAMP
SLOPER
R
S
R
R
RESETCOMP
+
-
R
SWITCH
+
-
+
-
OLPCOMP
R
ACTIVE
R
LOAD
LOOPC
OCPCOMP
+
-
IMAX
V _OUT
FB
Figure 3. Boost Converter Topology
MAGNETIC BOOST DC/DC CONVERTER ELECTRICAL CHARACTERISTICS
Symbol
I_LOAD
V_OUT
RDS_ON
f_PWM
Parameter
Maximum Continuous Load
Current
Output Voltage Accuracy
(FB Pin)
Switch ON Resistance
PWM Mode Switching
Frequency
Frequency Accuracy
t_PULSE
t_STARTUP
Switch Pulse Minimum
Width
Startup Time
I_MAX
SW Pin Current Limit
Test Conditions
3.0V = V_IN
V_OUT = 18V
3.0V ≤ V_IN ≤ 5.5V
V_OUT = 18V
I_SW = 0.5A
RT = 82 kΩ
RT = 82 kΩ
no load
Boost startup from STANDBY to V_OUT = 18V,
no load
Min
−3.5
−7
−9
Typ
0.15
1.0
45
15
800
Max
70
+3.5
0.3
+7
+9
1150
Unit
mA
%
Ω
MHz
%
ns
ms
mA
BOOST STANDBY MODE
User can set the Boost Converter to STANDBY mode by writing the register bit EN_BOOST low. When
EN_BOOST is written high, the converter starts for 20ms in low current PWM mode and then goes to normal
PWM mode. All LED outputs are off during the 20ms delay to ensure smooth startup.
BOOST OUTPUT VOLTAGE CONTROL
User can control the boost output voltage by Boost Output 8-bit register.
Boost Output [7:0]
Register 0DH
Bin
Dec
0000 1000
8
0000 1001
9
0000 1010
10
0000 1011
11
Boost Output
Voltage (typical)
8.0V
9.0V
10.0V
11.0V
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