ZXLD1322DCTC ZETEX [Zetex Semiconductors], ZXLD1322DCTC Datasheet - Page 12

• Manufacturer Part Number: ZXLD1322DCTC
• Description: Buck/boost mode DC-DC converter for LED driving with 700mA output and current control
• Manufacturer: ZETEX [Zetex Semiconductors]

PWM control
A wider dimming range can be achieved by applying a PWM control signal to the ADJ pin to turn
the device on and off, giving an average output current proportional to the duty cycle of the
control signal. The ADJ pin can be driven directly from the open drain NMOS output of a
microcontroller, or indirectly with a low saturation voltage NPN transistor such as the Zetex
ZXTN25015DFL. (Fig 2).
In the circuit of Fig 4, the average LED output current will be
Where duty cycle
A PWM frequency of 200Hz, or lower is recommended, to minimize errors due to the rise and fall
times of the converter output.
Issue 1 - January 2008
© Zetex Semiconductors plc 2008
I
D
LED
(
=
avg
(
)
T
1
T
+
=
2
T
) 2
I
LED
(
nom
* )
D
ZXTN25015DFL
Fig 1
Fig 2
12
ADJ
ZXLD1322
ZXLD1322
www.zetex.com