MAX1530_09 Datasheet, PDF (20/33 Pages) Maxim Integrated Products – Multiple-Output Power-Supply Controllers for LCD Monitors

Multiple-Output Power-Supply
Controllers for LCD Monitors
LR2 is typically used to generate the TFT LCD gamma
reference voltage, which is usually 0.3V below the
source drive supply voltage.
LR2 is enabled when the step-down regulator is
enabled and the voltage on ONL2 exceeds ONL2 input
threshold (1.238V typ). (See the Startup Sequence
(ONL_,SEQ) section.) Each time it is enabled, the con-
troller goes through a soft-start routine that ramps up its
internal reference DAC. (See the Soft-Start section).
Linear Regulator Controller (LR3)
LR3 is an analog gain block with an open-drain N-
channel output. It drives an external PNP pass transis-
tor with a 6.8kΩ base-to-emitter resistor. Its guaranteed
base drive sink current is at least 2mA. The regulator,
including Q3 in Figure 1, uses a 0.47µF output capaci-
tor and is designed to deliver 20mA at 25V. The regula-
tor including Q3 in Figure 2 uses a 4.7µF output
capacitor and is designed to deliver 500mA at 10V.
For the MAX1531 (Figure 1), LR3 is typically used to gen-
erate the TFT LCD gate driver’s gate-on voltage. A suffi-
cient input voltage can be produced using a
charge-pump circuit as shown in Figure 1. Note that the
voltage rating of the DRV3 output is 28V. If higher volt-
ages are present, an external cascode NPN transistor
(Q6) should be used with the emitter connected to
DRV3, the base to V_IN (which is the connection point of
C1 and R12 in Figure 1), and the collector to the base of
the PNP pass transistor (Figure 1). For the MAX1530
(Figure 2), LR3 is typically used to generate the TFT LCD
source drive supply voltage. The input for this regulator
can come directly from the input supply, be produced
from an external step-up regulator, or from an extra wind-
ing coupled to the main step-down regulator inductor.
LR3 is enabled when the step-down regulator is
enabled and the voltage on ONL3 exceeds the ONL3
input threshold (1.238V typ). (See the Startup Sequence
(ONL_,SEQ) section.) Each time it is enabled, the con-
troller goes through a soft-start routine that ramps up its
internal reference DAC. (See the Soft-Start section.)
Source Drive Regulator Controller (LR4)
(MAX1531 Only)
LR4 is an analog gain block with an open-drain N-
channel output. It drives an external PNP pass transis-
tor with a 1.5kΩ base-to-emitter resistor. Its guaranteed
base drive sink current is at least 10mA. The regulator
including Q4 in Figure 1 uses a 4.7µF output capacitor
and is designed to deliver 500mA at 10V. The regula-
tor’s fast transient response allows it to handle brief
peak currents up to 2A.
LR4 is typically used to generate the TFT LCD source
drive supply voltage. The input for this regulator can
come directly from the input supply, be produced from
an external step-up regulator, or from an extra winding
coupled to the main step-down regulator inductor.
LR4 is enabled when the step-down regulator is
enabled and the voltage on ONL4 exceeds the ONL4
input threshold (1.238V typ). (See the Startup
Sequence (ONL_,SEQ) section.) Each time it is
enabled, the regulator goes through a soft-start routine
that ramps up its internal reference DAC from 0V to
1.238V (typ). (See the Soft-Start section.)
The standard application circuit in Figure 1 powers the
LR4 regulator directly from the input supply and uses
the MAX1531’s general-purpose overcurrent protection
function to protect the input supply from excessive load
currents. (See the Overcurrent Protection section.)
Gate-Off Regulator Controller (LR5) (MAX1531 Only)
LR5 is an analog gain block with an open-drain P-chan-
nel output. It drives an external NPN pass transistor
with a 6.8kΩ base-to-emitter resistor. Its guaranteed
base drive sink current is at least 2mA. The regulator
including Q5 in Figure 1 uses a 0.47µF output capacitor
and is designed to deliver 10mA at -10V.
LR5 is typically used to generate the TFT LCD gate dri-
ver’s gate-off voltage. A negative input voltage can be
produced using a charge-pump circuit as shown in
Figure 1. Use as many stages as necessary to obtain
the required output voltage.
LR5 is enabled when the step-down regulator is
enabled and the voltage on ONL5 exceeds the ONL5
input threshold (1.238V typ). (See the Startup
Sequence (ONL_,SEQ) section.) Each time it is
enabled, the regulator goes through a soft-start routine
that ramps down its internal reference DAC from VL to
125mV (typ). (See the Soft-Start section.)
Internal 5V Linear Regulator (VL)
All MAX1530/MAX1531 functions, except the thermal
sensor, are internally powered from the on-chip, low-
dropout 5V regulator. The maximum regulator input
voltage (V_IN) is 28V. Bypass the regulator’s output (VL)
with at least a 1µF ceramic capacitor to AGND. The
V_IN-to-VL dropout voltage is typically 200mV, so when
V_IN is less than 5.2V, VL is typically V_IN - 200mV. The
internal linear regulator can source up to 30mA to sup-
ply the device, power the low-side gate driver, charge
the external boost capacitor, and supply small external
loads. When driving particularly large MOSFETs, little or
no regulator current may be available for external
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