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 10

μH 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

R1(Ω)

5

19.1

10

9.53

12

7.87

15

6.34

20

4.75