MAX1513 Datasheet, PDF (15/28 Pages) Maxim Integrated Products – TFT-LCD Power-Supply Controllers

TFT-LCD Power-Supply Controllers
Logic Linear-Regulator Controller
The logic linear-regulator controller (REG L) is an analog
gain block with an open-drain N-channel output. It dri-
ves an external PNP pass transistor with a 680Ω base-
to-emitter resistor (Figure 1). Its guaranteed base-drive
sink current is at least 10mA. The regulator, including
transistor Q1 in Figure 1, uses a 10µF ceramic output
capacitor and is designed to deliver 500mA at 3.3V.
Other output voltages and currents are possible by scal-
ing the pass transistor, input capacitor, and output
capacitor. See the Pass-Transistor Selection and
Stability Requirements sections.
REG L is typically used to generate low-voltage logic
supplies for the timing controller and the digital sec-
tions of the TFT-LCD source/gate-drive ICs.
REG L is automatically enabled when the input voltage
is above the UVLO threshold. Each time it is enabled,
the controller goes through a soft-start routine that
ramps up its internal reference DAC in 128 steps.
Gate-Off Linear-Regulator Controller
The gate-off linear-regulator controller (REG N) is an ana-
log gain block with an open-drain P-channel output. It dri-
ves an external NPN pass transistor with a 3.6kΩ
base-to-emitter resistor (Figure 1). Its guaranteed base-
drive source current is at least 2mA. The regulator,
including Q2 in Figure 1, uses a 0.47µF ceramic output
capacitor and is designed to deliver 30mA at -10V. Other
output voltages and currents are possible by scaling the
pass transistor, input capacitor, and output capacitor.
See the Pass-Transistor Selection and Stability Require-
ments sections.
REG N is typically used to provide the TFT-LCD gate dri-
vers’ gate-off voltage. A negative voltage can be pro-
duced using a charge-pump circuit as shown in Figure 1.
V_MAIN
FROM CHARGE-
PUMP OUTPUT
DRVP
NPN CASCODE
TRANSISTOR
MAX1513
MAX1514
FBP
PNP PASS
TRANSISTOR
V_GON
REG N is enabled after the logic linear-regulator REG L
soft-start has completed. Each time it is enabled, the
control goes through a soft-start routine that ramps
down its internal reference DAC from V_REF to 250mV in
about 100 steps.
Gate-On Linear-Regulator Controller
The gate-on linear-regulator controller (REG P) is an
analog gain block with an open-drain N-channel output.
It drives an external PNP pass transistor with a 6.8kΩ
base-to-emitter resistor (Figure 1). Its guaranteed base-
drive sink current is at least 1mA. The regulator includ-
ing Q3 in Figure 1 uses a 0.47µF ceramic output
capacitor and is designed to deliver 20mA at 25V.
Other output voltages and currents are possible by
scaling the pass transistor, input capacitor, and output
capacitor. See the Pass-Transistor Selection and
Stability Requirements sections.
REG P is typically used to provide the TFT-LCD gate
drivers’ gate-on voltage. Use a charge pump with as
many stages as necessary to obtain a voltage exceed-
ing the required gate-on voltage (see the Selecting the
Number of Charge-Pump Stages section). Note that the
voltage rating of the DRVP output is 28V. If the charge-
pump output voltage can exceed 28V, an external cas-
code-connected NPN transistor should be added
(Figure 6). Alternately, the linear regulator can control
an intermediate charge-pump state while regulating the
final charge-pump output (Figure 7).
REG P is enabled after the step-up regulator soft-start
has completed and the voltage on DEL exceeds 1.25V.
Each time it is enabled, the controller goes through a
soft-start routine that ramps up its internal reference DAC
in 128 steps.
0.1µF
0.1µF
LX
V_MAIN
13V
DRVP
6.8kΩ
Q1
MAX1513
MAX1514
FBP
0.47µF
267kΩ
1%
10.0kΩ
1%
V_GON
35V
0.22µF
Figure 6. Using an NPN Cascode for Charge-Pump Output
Voltages > 28V
Figure 7. Linear Regulator Controls Intermediate Charge-Pump
Stage
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