LP3936 Datasheet, PDF (13/20 Pages) National Semiconductor (TI) – Lighting Management System for Six White LEDs and One RGB or FLASH LED

Boost Output Voltage Control
User can control the boost output voltage by boost output 8-bit register.
Boost[7:0]
Register 0Dh
Binary
Hex
0000 0000 00
0000 0001 01
0000 0011 03
0000 0111 07
0000 1111 0F
0001 1111 1F
0011 1111 3F
0111 1111 7F
1111 1111 FF
BOOST Output
Voltage
(typical)
4.10
4.25
4.40
4.55 Default
4.70
4.85
5.00
5.15
5.30
Boost Output Voltage Control
20081418
Magnetic Boost DC/DC Converter Electrical Characteristics
Symbol
Parameter
I_LOAD
Load Current
V_OUT Output Voltage Accuracy (FB Pin)
Output Voltage (FB Pin)
RDS_ON
f_PWF
Switch ON Resistance
PWM Mode Switching Frequency
Frequency Accuracy
Conditions
3.0V ≤ V_IN ≤ 4.5V
V_OUT = 4.55V
1 mA ≤ I_LOAD ≤ 225 mA
3.0V ≤ V_IN ≤ V (FB)−0.5V
V_OUT = 4.55V
1 mA ≤ I_LOAD ≤ 250 mA
3.0V < V_IN < 4.55V +
V_(SCHOTTKY)
1 mA ≤ I_LOAD ≤ 250 mA
V_IN > 4.55V + V_(SCHOTTKY)
V_DD1,2 = 3.6V, I_SW = 0.5A
RT = 82 kΩ
RT = 82 kΩ
t_STARTUP Startup Time
I_{CL_OUT} OUT Pin Current Limit
V_DD = 3.6V
Min
Typ
0
−5
4.55
V_IN– V_(SCHOTTKY)
0.4
1
−6
±3
−10
25
600
750
400
Max
250
+5
0.5
+6
+10
1050
1200
Units
mA
%
V
V
Ω
MHz
%
ms
mA
PFM/PWM Mode
User can change the Boost converters mode between PWM (Pulse Width Modulation) and PFM (Pulse Frequency Modulation).
The startup is done on PFM mode and then the device runs on PWM mode (as a default). User can set PFM mode by turning
“pfm_mode” register bit HIGH. PFM is recommended to use with light loads and PWM with high loads.
Boost Standby Mode
User can set boost converter to STANDBY mode by writing register bit EN_BOOST low. This mode can be useful when driving
LEDs directly from battery voltage. This may be possible if LED forward voltage is low, battery voltage is high and LED current
is low.
When EN_BOOST is written high, the converter starts for 10 ms in PFM mode and then goes to PWM mode if PWM mode has
been selected (default).
Unused Boost Converter
If the boost converter is not used, it should be disabled by writing bit en_boost low. OUT pin should be connected to GND and
FB pin to the LED supply voltage.
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