tk65933 Crystalfontz America, Inc.,, tk65933 Datasheet - Page 10

• Manufacturer Part Number: tk65933
• Description: Large El Lamp Driver Features
• Manufacturer: Crystalfontz America, Inc.,

With properly selected components, the TK6593x will
nominally support peak output voltages to 90 V
(180 V
from the driver outputs, the removal of the load can cause
the output voltage to increase beyond 90 V. To protect
against this fault condition, a clamp circuit exists on the
high voltage output which nominally limits the output
voltage to a typical value of 105 V (210 V
In an effort to extend EL lamp life, reduce EMI emissions,
and reduce the power draw of the IC, current sources to
control the charging and discharging of the EL lamp panel
and special sequencing control of the H-bridge FETs were
added to the H-bridge of TK659xx.
Current sources were added between ground and the
sources of the low-side N-channel FETs (Figure 2).
Therefore, the current into and out of the EL panel is
controlled and limited.
The FETs are turned off and on in the sequence shown in
Figure 3. As is noted in Figure 3, there is a period of time
when both of lower N-channel FETs are turned on and both
of upper P-channel FETs are turned off. This provides a
period of time to discharge the EL panel capacitance
completely; before starting to recharge it again with current
from HV voltage rail. Therefore, this special sequencing
method prevents taking current off the HV voltage rail
during the discharge of EL panel capacitance and operates
more efficiently.
TK6593xM
Page 10
THEORY OF OPERATION (CONT.)
H-BRIDGE SECTION OPERATION
PK-PK
DETAILS CONCERNING THE
). Should the EL Panel become disconnected
PK-PK
).
FIGURE 3: H-BRIDGE SEQUENCING WAVEFORMS
Current Source 1
V EL =
V EL + V EL -
FIGURE 2: H-BRIDGE SCHEMATIC
UL
UR
LL
LR
V EL -
V EL +
-
EL -
HVP
OFF
OFF
ON
ON
UL
BOTH OFF
LL
BOTH ON
EL Panel
Capacitance
Discharging
OFF
OFF
EL Panel
ON
ON
HV
February 2001 TOKO, Inc.
UR
LR
OFF
OFF
ON
ON
HVP
EL +
Current Source 2
OFF
OFF
ON
ON