ISL97649B Ver la hoja de datos (PDF) - Intersil
Número de pieza
componentes Descripción
fabricante
ISL97649B Datasheet PDF : 19 Pages
| |||
ISL97649B
VIN
UVLO
THRESHOLD
0
VGH
RESET
VDPM
1.215V
VFLK
VGHM
VGH
VTOGHVisMGfHIoSrWcFeHOdERtNCoEVDIN
GPM_LO
FALVLGS HTOwUhVeLnORAENSDET
SlLoOpPeEisIScontrolled
VGHgo>e3sVto low AND
bCyORNTEROLLED BY RE
VGH>3V
POPWowERer-OoNn DdeElLaAyYtiTmIMeE
DDEeLlaAyYtiTmIMeEisIScontrolled
COisNcToRnOtrLoLlEleDd BbYy CDPM
CDPM
bCyOCNTEROLLED BY CE
FIGURE 12. GATE PULSE MODULATOR TIMING DIAGRAM
VCOM Amplifier
The VCOM amplifier is designed to control the voltage on the
back plane of an LCD display. This plate is capacitively coupled to
the pixel drive voltage, which alternately cycles positive and
negative at the line rate for the display. Thus, the amplifier must
be capable of sourcing and sinking pulses of current, which can
occasionally be quite large (in the range of 100mA for typical
applications).
The ISL97649B VCOM amplifier output current is limited to
225mA typical. This limit level, which is roughly the same for
sourcing and sinking, is included to maintain reliable operation
of the part. It does not necessarily prevent a large temperature
rise if the current is maintained. (In this case, the whole chip may
be shut down by the thermal trip to protect functionality.) If the
display occasionally demands current pulses higher than this
limit, the reservoir capacitor will provide the excess and the
amplifier will top the reservoir capacitor back up once the pulse
has stopped. This will happen in the µs time scale in practical
systems and for pulses 2 or 3 times the current limit, the VCOM
voltage will have settled again before the next line is processed.
DCP (Digitally Controlled Potentiometer)
Figure 13 shows the relationship between the register value and
the resistor string of the DCP. Note that the register value of zero
actually selects the first step of the resistor string. The output
voltage of DCP is given by Equation 8:
VDCP
=
⎛
⎝
R-----e---g----i--s---t--e--2--r-5--V--6-a----l--u----e----+-----1--⎠⎞
⎛
⎝
A----2V----D0---D--⎠⎞
(EQ. 8)
AVDD
19R
AVDD
20
R
REGISTER VALUE
255
254
253
VDCP
252
251
2
1
0
FIGURE 13. SIMPLIFIED SCHEMATIC OF DIGITALLY
CONTROLLED POTENTIOMETER (DCP)
Current Sink
Figure 14 shows the schematic of the POS pin current sink. The
circuit is made up of amplifier A1, transistor Q1, and resistor
RSET, which form a voltage controlled current source.
12
FN7927.0
December 5, 2011
Share Link: 