TS19371CX6
Taiwan Semiconductor
4 Version: J1708
APPLICATION INFORMATION
Operation
The TS19371 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.
Soft Start and Current Limit
The internal soft start circuit minimizes the inrush current during turning on TS19371. The Typical switch current is
limited to about 650mA by the chip.
Over Voltage Protection
The TS19371 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 TS19371 will shutdown until input
condition changes to bring it out of the shutdown mode.
Inductor Selection
A 10μH inductor is recommended for most TS19371 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
Schottky diodes, with their low forward voltage drop and fast reverse recovery, are the ideal choices for TS19371
applications. The forward voltage drop of a Schottky diode represents the conduction losses in the diode while the
diode capacitance (CT or CD) represents the switching losses. For diode selection, both forward voltage drop and
diode capacitance need to be considered. 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 TS19371. A Schottky diode rated at 1000mA is sufficient for most TS19371 applications.
Capacitor Selection
The small size of ceramic capacitors makes them ideal for TS19371 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 4.7µF input capacitor and a 4.7µF output capacitor are sufficient for most TS19371
applications.
LED Current Control
The LED current is controlled by the feedback resistor (R1). The feedback reference is 95mV. The LED current is
95mV/R1. The formula and table 3 for R1 selection are shown below. R1=95mV/I
LED
