Analog Devices ADP50460008 Owner's Manual page 32

ADP50460008
Channel 7 Backlight Boost Regulator and
LED Driver
The Channel 7 boost regulator has a constant-current sink
LED driver. An external resistor connected to ISET7 defines the
reference current for the LED driver. The LED current is pro-
2
grammable through the I C interface in 32 steps. An external
PWM interface circuit, connected to ISET7, can be used in
applications where the LED brightness must be controlled with
fine adjustments. The PWM interface circuit is based on an RC
filter producing a dc level that is proportional to the duty cycle
of the PWM signal supplied from an external microprocessor.
Channel 7 is an asynchronous, current mode regulator that
supports up to four LEDs connected in series. The operating
switching frequency of this boost regulator can be 1.25 MHz
or 2.5 MHz. The frequency selection is a factory-programming
LSTR7
4B
BLGND7
3A
ISET7
3C
CURRENT SENSE AMP
MAX DUTY
PWM COMP
ERROR AMP
2.5MHz
REF
Figure 56. Channel 7 Backlight Boost Regulator Block Diagram
option with a default value of 2.5 MHz. Channel 7 includes an
overvoltage detection circuit that protects the regulator in case
of an LED failure or string disconnection. The overvoltage
protection is a latched event with a delay to avoid false
triggering.
Channel 7 has a programmable soft start ramp that is controlled
by Bit 1 in Register SFTTIM at Address 2 (see Table 16, Table 17,
and Table 21). The LED current for Channel 7 is controlled by
Bits[7:3] in Register VID78 at Address 11 (see Table 42 and
Table 43). The overvoltage protection status for Channel 7 can
be tested by reading Bit 6 in Register OVPST at Address 13 (see
Table 47 and Table 48). The forward voltage of the LEDs used in
the application affects the selected soft start time. The regulator
on/off activation for Channel 7 is controlled by Bit 2 in Register
PCTRL at Address 32 (see Table 51 and Table 52).
REF
SAFETY AMP
Rev. Sp0 | Page 32 of 60
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SW7
1A
+
Li+
–
PGND7
PGND7
2A
OVP7
3B