Diodes AP3616 - Manual (Page 12)

SIXTEEN-CHANNEL, 75mA CURRENT SINK WITH CURRENT MATCH AP3616
Data Sheet
12
BCD Semiconductor Manufacturing Limited Jul. 2012 Rev. 1. 2
Function Description
1. LED Current Setting
The maximum LED current per channel can be
adjusted up to 75mA via ISET pin. When ≥ 75mA
current is needed in application, two or more channels
can be paralleled to provide larger drive current. Con-
nect a resistor R
ISET
between ISET pin and GND to
set the reference current I
SET
. The LED current is
determined by the following equation.
2. Dimming Control
The AP3616 provides two dimming methods: external
PWM signal or DC voltage input. Applying a PWM
signal to DIM pin to adjust the LED current, that
means, the LED current of all enabled channels can be
adjusted at the same time and the LED brightness can
be adjusted from 1%*I
CHX_MAX
to 100%*I
CHX_MAX
.
During the high level period of PWM signal, the LED
is turned on and 100% of the current flows through
LED, while during the low level period of the PWM
signal, the LED is turned off and almost no current
flows through the LED, thus changing the average
current through LED and finally adjusting LED
brightness. The external PWM signal frequency
applied to PWM pin is allowed to be 80Hz or higher.
3.Over Voltage Protection
The AP3616 integrates an OVP circuit. The OVP pin
is connected to the center tap of voltage-divider (R
OV3
and R
OV4
) that placed between high voltage output
and GND (Figure 19). If the voltage on OVP pin
exceeds 1.194V, which may results from open loop or
excessive output voltage, the AP3616 will start LED
open protection.
4. LED Short-circuit Protection
The AP3616 integrates an LED short-circuit
protection circuit. During normal operation, any short-
circuited LED will cause the corresponding LED pin
voltage to rise. If any LED pin voltage exceeds 8
times of the voltage at SCP pin, the corresponding
LED current sink will be latched off, while the
remaining string(s) keep normal operation. Toggle the
VIN and/or EN to reset the latch. An internal current
source was connected to this pin, a resistor connected
here is used to set the shorting LED trigger voltage.
5. LED Open-circuit Protection
The AP3616 integrates an LED Open-Circuit Protec-
tion circuit. When any LED string is open, V
OUT
will
boost up until the voltage at OVP pin reaches an
approximate 1.194V threshold. The IC will automati-
cally ignore the open string(s) whose CHX pin voltage
is less than 100mV.
) (
194 . 1 0 156
) (
) (
Ω
×
=
Ω
⋅
=
k R k R
V k
mA I
ISET ISET
ISET
LED
OV4
OV4 OV3
OVP R
V 194 . 1 ) R (R
V
Ч +
=