TS19378 Datasheet, PDF (4/7 Pages) Taiwan Semiconductor Company, Ltd – 2A Buck (Step-down) WLED Driver

TS19378
2A Buck (Step-down) WLED Driver
Function Descriptions
PWM Control
The TS19378 consists of DC/DC converters that employ a pulse-width modulation (PWM) system. In converters of
the TS19378, the pulse width varies in a range from 0 to 100%, according to the load current. The ripple voltage
produced by the switching can easily be removed through a filter because the switching frequency remains
constant. Therefore, these converters provide a low-ripple power over broad ranges of input voltage and load
current
Setting I_LED Current
Application circuit item shows the basic application circuit with TS19378 adjustable output version. The external
resistor sets the LED output current according to the following formula:
I_LED=(0.25V/R5), V_FB=0.2V
Resistor select for LED output current setting
I_LED
350mA
R2
0.57Ω
70mW
750mA
0.266Ω
150mW
1000mA
0.2Ω
200mW
Current Liming
The current limit threshold is setting by the internal circuit.
Compensation
In all LED driver applications. Connecting a resistor (R2) and a capacitor (C7) from COMP pin to GND. Please
refer the application circuit table to design.
EN/SS
This pin can be supplied shutdown or soft start function. It is inside pull high function. For normal application, the
pin must be connected a capacitor to ground. There is a 5uA current to charge this capacitor, vary the different
capacitor value to control soft start time. Allow the switching regulator circuit to be shutdown pulling this pin below
a 0.8V threshold voltage; the shutdown supply current is approximately 150uA
Inductor Selection
For most designs, the different frequency can be reducing the inductor value; The TS19378 is suggested 33uH.
Where is inductor Ripple Current. Large value inductors lower ripple current and small value inductors result in high
ripple currents. Choose inductor ripple current approximately 20% of the maximum load current 2A, ∆IL=0.4A. The
DC current rating of the inductor should be at least equal to the maximum load current plus half the ripple current to
prevent core saturation (2A+0.2A).
Input Capacitor Selection
This capacitor should be located close to the IC using short leads and the voltage rating should be approximately
1.5 times the maximum input voltage. The RMS current rating requirement for the input capacitor of a buck
regulator is approximately 1⁄2 the DC load current. A low ESR input capacitor sized for maximum RMS current
must be used. A 220µF low ESR capacitor for most applications is sufficient.
Over Voltage Protection
The OVP voltage is set by outside resistance (R1 and R4). The external resistor sets the OVP voltage according to
the following equation:
R4
V_OUT (OVP) =
V_OVP
× (1+
)
R1
If V_OVP >0.85V, The OVP is happened that to disable the driver until V_OVP <0.85V.
4/7
Version: A13