LP3936 Datasheet, PDF (15/30 Pages) National Semiconductor (TI) – Lighting Management System for Six White LEDs and One RGB or FLASH LED

LP3936
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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
SNVS259D – NOVEMBER 2003 – REVISED MAY 2013
Min
Typ
Max Units
0
250
mA
−5
+5
%
4.55
V
V_IN–V_(SCHOTTKY)
V
0.4
0.5
Ω
1
MHz
−6
±3
+6
%
−10
+10
25
ms
600
750
1050
mA
400
1200
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). During Boost Start-up all LEDs are turned off to reduce the load.
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.
Copyright © 2003–2013, Texas Instruments Incorporated
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