TS19370_10 Datasheet, PDF (4/8 Pages) Taiwan Semiconductor Company, Ltd – Boost (Step-up) WLED Driver with OVP

TS19370
Boost (Step-up) WLED Driver with OVP
Application Information
Operation
The TS19370 uses a constant frequency, current mode control scheme to provide excellent line and load
regulation. Operation can be best understood by referring to the block diagram. At the start of each oscillator cycle,
the RS latch is set, which turns on the power switch Q1. A voltage proportional to the switch current is added to a
stabilizing ramp and the resulting sum is fed into the positive terminal of the PWM comparator A2. When this
voltage exceeds the level at the negative input of A2, the RS latch is reset turning off the power switch. The level at
the negative input of A2 is set by the error amplifier A1, and is simply an amplified version of the difference
between the feedback voltage and the reference voltage of 95mV. In this manner, the error amplifier sets the
correct peak current level to keep the output in regulation. If the error amplifier’s output increases, more current is
delivered to the output; if it decreases, less current is delivered.
Minimum Output Current
The TS19370 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 20mA operation. As the
current is further reduced, the device will begin skipping pulses. This will result in some low frequency ripple,
although the LED current remains regulated on an average basis down to zero.
Soft Start and Current Limit
The internal soft start circuit minimizes the inrush current during turning on TS19370. The Typical switch current is
limited to about 320mA by the chip.
Over Voltage Protection
The TS19370 has design an internal latched off open-circuit protection circuit, the additional sense pin to detect the
voltage when the LEDs are disconnected from the circuit or fail open, the TS19370 will shutdown until input
condition changes to bring it out of the shutdown mode.
Inductor Selection
A 22µH inductor is recommended for most TS19370 applications. Although small size and high efficiency are major
concerns, the inductor should have low core losses at 1.2MHz and low DCR (copper wire resistance).
Diode Selection
To maintain high efficiency, the average current rating of the Schottky diode should be large than the peak inductor
current, IPK. Schottky diode with a low forward drop and fast switching speeds are ideal for increase efficiency in
portable application. Choose a reverse breakdown of the Schottky diode large than the output voltage. A Schottky
diode rated at 100mA to 200mA is sufficient for most TS19370 applications.
Capacitor Selection
The small size of ceramic capacitors makes them ideal for TS19370 applications. X5R and X7R types are
recommended because they retain their capacitance over wider voltage and temperature ranges than other types
such as Y5V or Z5U. A 1µF input capacitor and a 0.22µF output capacitor are sufficient for most.
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Version: D08