LM1937 HTC Korea TAEJIN Technology Co., LM1937 Datasheet
LM1937
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LM1937 Summary of contents
Page 1
... MP3 Players • GPS Receivers DESCRIPTION The LM1937 is a step-up DC/DC converter specifically designed to drive white LEDs with a constant current. The device can drive two, three or four LEDs in series from a Li-Ion cell. Series connection of the LEDs provides identical LED currents resulting in uniform brightness and eliminating the need for ballast resistors. The output capacitor can be as small as 0.22µ ...
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... BLOCK DIAGRAM ABSOLUTE MAXIMUM RATING Input Voltage (Vin) SW Voltage FB Voltage Voltage SHDN Operating Temperature (Topr) Maximum Junction Temperature Storage Temperature (Tstg) Lead Temperature (soldering, 5 sec) (Note +70 °C 125 °C -65 ~+125 °C 260 °C − 2 − LM1937 HTC ...
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... Minimum Output Current The LM1937 can regulate three series LEDs connected at low output currents, down to approximately 4mA from a 4.2V supply, without pulse skipping, using the same external components as specified for 15mA operation. As current is further reduced, the device will begin skipping pulses ...
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... Schottky diodes with higher current ratings usually have lower forward voltage drop and larger diode capacitance, which can cause significant switching losses at the 1.2MHz switching frequency of the LM1937. A Schottky diode rated at 100mA to 200mA is sufficient for most LM1937 applications. Some recommended Schottky diodes are listed in Table 3. ...
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... Using a PWM Signal to SHDN Pin With the PWM signal applied to theSHDN pin, the LM1937 is turned on or off by the PWM signal. The LEDs operate at either zero or full current. The average LED current increases proportionally with the duty cycle of the PWM signal duty cycle will turn off the LM1937 and corresponds to zero LED current ...
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... WHITE LED STEP-UP CONVERTER Figure 6. Dimming Control Using a Filtered PWM Signal − 6 − LM1937 HTC ...