Sony BVM-L230 Service Manual page 78

. Latching of LED driver errors (XERR: open error and
temperature defect)
Among the error signals (XERR) of a LED driver, an
open detection error can be detected only during driving
because of IC specifications. Therefore, it is uncertain
that the error can be detected during ordinary PWM
control. For this reason, the error signal (XERR) from a
driver is input to pin 25, latched during error detection
(H → L), and output to an H8 microcomputer (to pin 33
of ERR_IN). Latching is canceled using the clear signal
(input signal at pin 23 of ERR_CLR) from an H8
microcomputer.
2. Peripheral circuits of LED driver (TLC5941)
. Forty-eight L/S (write source) (x 4 channels) LED is
driven using twelve 16-channel LED drivers (IC6502 to
IC6513).
. Data signals (SIN and SOUT) are connected in series
with the H8 microcomputer (IC6704) as a starting point.
. An SCLK clock is distributed from an H8
microcomputer to each IC through a clock buffer
(IC6500 and IC6501). A GSCLK clock is distributed
from CPLD (IC6900) to each IC through a clock buffer
(IC6500 and IC6501).
. Blanking signals (BLANK_A to BLANK_M) are
generated using CPLD and supplied to each IC.
Setting current
. In hardware, maximum setting current I max is set using
a resistance value (Riref) connected to IREF (pin 27).
The current maximum setting current is as follows:
. Imax = 44.4 mA
. The current during unit shipping is set by software.
. The current default setting is R: 33.1 mA, G: 29.6 mA,
and B: 39.5 mA.
Terminal overvoltage applying protection circuit
A terminal applied voltage is 17 V (maximum) because of
IC specifications. Therefore, only the green/blue drive
terminal in which 17 V or more is applied is limited to 12
V (maximum) by the gate grounding of FET (Q6601 to
Q6791) (by applying 12 V (BL_12V) from LMD1 to a
gate voltage).
2-10
LED leak inspection circuit
The maximum current setting of a LED driver is changed
to inspect the minute leak of LED.
By setting the control line (LK_CHK_X) from an H8
microcomputer from high to low, FET is turned off and
Viref is changed from 0.8 kZ to 680 kZ. In this case,
Imax becomes 57 µA.
This leak is inspected in each color output current of about
10 µA by software setting.
BVM-L230