TS19452 Datasheet, PDF (3/7 Pages) Taiwan Semiconductor Company, Ltd – AC/DC WLED Driver with Internal MOSFET

TS19452
AC/DC WLED Driver with Internal MOSFET
Universal Switch Mode
Function Description
The TS19452 is a PWM peak current controller for controlling a buck converter topology in continuous conduction
mode (CCM). The output current is internally preset at 100mA
When the input voltage of 20~400V appears at the Drain pin, the internal high-voltage linear regulator seeks to
maintain a voltage of 7.5VDC at the VDD pin. Until this voltage exceeds the internally programmed under-voltage
threshold, the output switching MOSFET is non-conductive. When the threshold is exceeded, the MOSFET turns
on. The input current begins to flow into the Drain pin. Hysteresis in provided in the under-voltage comparator to
prevent oscillation.
When the input current exceeds the internal preset level, a current sense comparator resets an RS flip-flop, and the
MOSFE turns off, At the same time, a one-shot circuit is activated that determines the duration of the off-state
(12µS typ.) As soon as this time is over, the flip-flop sets again. The new switching cycle begins.
A “blanking” delay of 300nS is provided that presents false triggering of the current sense comparator due to the
leading edge spike caused by circuit parasitic.
Application Information
The TS19452 is specifically designed for driving multi LED strings. It can be operated from either universal AC line
range of 85~264VAC or 20~400VDC, and drives up to tens of high brightness LEDs. All LEDs can be run in series
and this device regulates at constant current, yielding uniform illumination.
Selecting L1 and D1
There is a certain trade-off to be considered between optimal sizing of the output inductor L1 and the tolerated
output current ripple. The required value of L1 is inversely proportional to the ripple current ∆I_O in it.
L1 = (V_O x T_OFF) / ∆I_O
V_O is the forward voltage of the LED string. T_OFF is the off-time of the TS19452. The output current in the LED string
(I_O) is calculated as:
I_O = I_H – (∆I_O / 2)
Where I_TH is the current sense comparator threshold. The ripple current introduces a peak-to-average error in the
output current setting that needs to be accounted for. Due to constant off-time control technique used in the
TS19452, the ripple current is independent of the input AC or DC line voltage variation. Therefore, the output
current will remain unaffected by the varying input voltage.
According a filter capacitor across the LED string can reduce the output current ripple even further, thus permitting
a reduced value of L1. However, one must keep in mind that the peak-to-average current error is affected by the
variation of T_OFF. Therefore, the initial output current accuracy might be sacrificed at large ripple current in L1.
Another important aspect of designing an LED driver with TS19452 is related to certain parasitic elements of the
circuit, including distributed coil capacitance of L1, junction capacitance and reverse recover of the rectifier diode
D1, capacitance of the PCB traces C_PCB and output capacitance C_DRAIN of the controller itself. These parasitic
elements affect the efficiency of the switching converter and could potentially cause false triggering of the current
sense comparator if not properly managed. Minimizing these parasitic is essential for efficient and reliable
operation of the TS19452.
Coil capacitance of inductors is typically provided in the manufacturer’s data books either directly or in terms of the
self-resonant frequency (SRF).
SRF = 1 / (2π · √ (L · CL))
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Version: A12