LTC3202 Datasheet, PDF (10/12 Pages) Linear Technology – Low Noise, High Efficiency Charge Pump for White LEDs

LTC3202
U
OPERATIO
Layout Considerations
Due to its high switching frequency and the transient
currents produced by the LTC3202, careful board layout is
necessary. A true ground plane and short connections to
all capacitors will improve performance and ensure proper
regulation under all conditions. Figure 6 shows the recom-
mended layout configurations.
The flying capacitor pins C1⁺, C2⁺, C1^– and C2^– will have
very high edge rate waveforms. The large dv/dt on these
pins can couple energy capacitively to adjacent printed
circuit board runs. Magnetic fields can also be generated
if the flying capacitors are not close to the LTC3202 (i.e.
the loop area is large). To decouple capacitive energy
transfer, a Faraday shield may be used. This is a grounded
PC trace between the sensitive node and the LTC3202
pins. For a high quality AC ground it should be returned to
a solid ground plane that extends all the way to the
LTC3202.
Thermal Management
For higher input voltages and maximum output current
there can be substantial power dissipation in the LTC3202.
If the junction temperature increases above approxi-
mately 160°C the thermal shutdown circuitry will auto-
matically deactivate the output. To reduce the maximum
junction temperature, a good thermal connection to the
PC board is recommended. Connecting the GND pin (Pin
5 and Pin 11 on the DFN package) to a ground plane, and
maintaining a solid ground plane under the device can
reduce the thermal resistance of the package and PC
board considerably.
Brightness Control Using Pulse Width Modulation
An alternative approach to dimming is to use pulse width
modulation rather than the internal digital to analog con-
verter. By connecting both the D0 and D1 pins to a PWM
signal, continuous brightness control can be achieved.
Frequencies from 100Hz to 500Hz are acceptable with a
1µF to 4.7µF output capacitor.
V_OUT
GND
V_IN
D1
D0
V_{OUT VIN}
V_{D0, D1}
10
D0
1
LTC3202
D1
t
3202 F07
Figure 7. Alternative Brightness Control
GND
3202 F06
Figure 6. Recommended Layouts
3202fa
10