ISL97642 Просмотр технического описания (PDF) - Renesas Electronics
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ISL97642 Datasheet PDF : 19 Pages
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ISL97642
VBOOST
LX
0.9V
PG_LDOP +
-
+
-
GMP
LDO_ON
36V
ESD
CLAMP
RBP
700
DRVP
FBP
RP1
RP2
20k
1: Np
0.1µF
CP (TO 36V)
0.1µF
VON (TO 35V)
CON
FIGURE 18. VON FUNCTIONAL BLOCK DIAGRAM
LX
0.1µF
PG_LDON -
+
0.4V
LDO_OFF
VREF
FBN
RN2
20k
1: Nn
-
+
GMN
36V
ESD
CLAMP
RN1
DRVN
RBN
700
CP (TO -26V)
0.1µF
VOFF (TO -20V)
COFF
FIGURE 19. VOFF FUNCTIONAL BLOCK DIAGRAM
The VON power supply is used to power the positive supply of
the row driver in the LCD panel. The DC/DC consists of an
external diode-capacitor charge pump powered from the
inductor (LX) of the boost converter, followed by a low dropout
linear regulator (LDO_ON). The LDO_ON regulator uses an
external PNP transistor as the pass element. The onboard
LDO controller is a wide band (>10MHz) transconductance
amplifier capable of 5mA output current, which is sufficient for
up to 50mA or more output current under the low dropout
condition (forced beta of 10). Typical VON voltage supported by
ISL97642 ranges from +15V to +36V. A fault comparator is
also included for monitoring the output voltage. The
undervoltage threshold is set at 25% below the 1.2V reference.
The VOFF power supply is used to power the negative supply
of the row driver in the LCD panel. The DC/DC consists of an
external diode-capacitor charge pump powered from the
inductor (LX) of the boost converter, followed by a low dropout
linear regulator (LDO_OFF). The LDO_OFF regulator uses an
external NPN transistor as the pass element. The onboard
LDO controller is a wide band (>10MHz) transconductance
amplifier capable of 5mA output current, which is sufficient for
up to 50mA or more output current under the low dropout
condition (forced beta of 10). Typical VOFF voltage supported
by ISL97642 ranges from -5V to -25V. A fault comparator is
also included for monitoring the output voltage. The
undervoltage threshold is set at 200mV above the 0.2V
reference level.
Set-up Output Voltage
Refer to the “Typical Application Circuit” on page 18. The
output voltages of VON, VOFF and VLOGIC are determined by
Equations 9 and 10:
VON
=
VR
E
F
1
+
RR-----11---21-
(EQ. 9)
VOFF = VREFN + RR-----22---21- VREFN – VREF
(EQ. 10)
Where VREF = 1.2V, VREFN = 0.2V.
High Charge Pump Output Voltage (>36V)
Applications
In the applications where the charge pump output voltage is
over 36V, an external NPN transistor needs to be inserted in
between the DRVP pin and the base of pass transistor Q3, as
shown in Figure 20, or the linear regulator can control only one
stage charge pump and regulate the final charge pump output,
as shown in Figure 21.
VIN
CHARGE PUMP
OR VBOOST OUTPUT
700
DRVP
Q11
NPN
CASCODE
TRANSISTOR
ISL97642
VON
FBP
FIGURE 20. CASCODE NPN TRANSISTOR CONFIGURATION
FOR HIGH CHARGE PUMP OUTPUT VOLTAGE
(>36V)
FN6436 Rev 0.00
June 18, 2007
Page 13 of 19
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