ISL78020 Datasheet, PDF (13/19 Pages) Intersil Corporation – Automotive Grade TFT-LCD DC/DC with Integrated Amplifiers

ISL78020, ISL78022
V_BOOST
LX
0.9V
PG_LDOP ₊
-
+
-
GMP
LDO_ON
36V
ESD
CLAMP
R_BP
700Ω
DRVP
FBP
R_P1
R_P2
20kΩ
1: Np
0.1µF
CP (TO 36V)
0.1µF
V_ON (TO 35V)
C_ON
FIGURE 18. V_ON FUNCTIONAL BLOCK DIAGRAM
LX
0.1µF
PG_LDON _-
+
0.4V
LDO_OFF
V_REF
FBN
R_N2
20kΩ
CP (TO -26V)
0.1µF
1: Nn
-
+
GMN
36V
ESD
CLAMP
R_N1
DRVN
R_BN
700Ω
V_OFF (TO -20V)
C_OFF
FIGURE 19. V_OFF FUNCTIONAL BLOCK DIAGRAM
The V_ON 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
on-board 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
V_ON voltage supported by ISL78020 and ISL78022 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 V_OFF 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 on-board 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 V_OFF voltage supported by ISL78020 and
ISL78022 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 “Typical Application Circuit” on page 18, the output
voltages of V_ON, V_OFF and V_LOGIC are determined by
Equations 10 and 11:
V_ON
=
V_R
E
F
×
⎛
⎜1
⎝
+
RR_{-----11---21-⎠⎟⎞}
(EQ. 10)
V_OFF
=
V_R
E
F
N
+
R_-----2---2-
R₂₁
×
(V_R
E
FN
–
V_RE
F
)
(EQ. 11)
Where: V_REF = 1.2V, V_REFN = 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.
V_IN
CHARGE PUMP
OR V_{BOOST OUTPUT}
700Ω
DRVP
Q11
NPN
CASCODE
TRANSISTOR
ISL7802x
V_ON
FBP
FIGURE 20. CASCODE NPN TRANSISTOR CONFIGURATION
FOR HIGH CHARGE PUMP OUTPUT VOLTAGE
(>36V)
13
FN6386.2
December 6, 2007