MAX1997ETJ Maxim Integrated Products, MAX1997ETJ Datasheet - Page 21

• Manufacturer Part Number: MAX1997ETJ
• Description: LCD Drivers
• Manufacturer: Maxim Integrated Products

Specifications of MAX1997ETJ

• Dc: 0618
• Lead Free Status / Rohs Status: No

The maximum inductor current, input voltage, output
voltage, and switching frequency determine the induc-
tor value. To ensure an adequate inductor current-
sense signal in the IC, always calculate the inductor
value with the maximum guaranteed inductor current
even though the actual operating current may be much
lower. For the MAX1997/MAX1998, the maximum guar-
anteed inductor current is the minimum value of the
internal LX current limit (1.6A, see the Electrical
Characteristics). The equations provided here include a
constant defined as LIR, which is the ratio of the peak-
to-peak inductor current ripple to the average DC
inductor current. For a good compromise between the
size of the inductor, power loss, and output voltage rip-
ple, select an LIR of 0.3 to 0.5. The inductance value is
then given by:
where f
trical Characteristics), and I
the typical application circuit, the typical input voltage
is 3.3V, the main output voltage is 9V, and the switching
frequency is 1.5MHz. Based on the above equations,
the inductance value is 4.3µH for an LIR of 0.2. The
inductance value is 1.7µH for an LIR of 0.5. The induc-
tance in the standard application circuit is chosen to be
3.3µH.
Figure 8. Startup and Fault Protection Logic
Quintuple/Triple-Output TFT LCD Power Supplies
L
OSC
=



V
V
IN(TYP)
is the oscillator frequency (see Elec-
MAIN
STEP-UP REGULATOR FAULT
______________________________________________________________________________________
OVERCURRENT FAULT



REFERENCE READY



THERMAL FAULT
with Fault Protection and VCOM Buffer
V
MAIN
REG N FAULT
REG P FAULT
REG 2 FAULT
REG 1 FAULT
I
L(MAX) OSC
f
L(MAX)
OSC
SHDN
UVLO
FREQ
PFLT
- V
/128
IN(TYP)
f
is 1.6A. Considering






CLK
FAULT TIMER
LIR
COUNTER
1
RIPPLE
R



R
S
LATCH
FAULT
Q
STEP-UP REGULATOR
SOFT-START DONE
V
V
V
CT
CT
CT
The inductor’s peak current rating should be higher
than the expected peak inductor current throughout the
normal operating range. The expected peak inductor
current is given by:
where η is the efficiency of the regulator. For most
applications, the efficiency is between 75% and 85%.
Under fault conditions, the inductor current may reach
the internal LX current limit (see Electrical Character-
istics). However, soft saturation inductors and the con-
troller’s fast current-limit circuitry protect the device
from failure during such a fault condition.
The inductor’s DC resistance can significantly affect
efficiency due to the resistive power loss (P
can be approximated by the following equation:
where I
the inductor’s series resistance. For best performance,
select inductors with resistance less than the internal
N-channel MOSFET’s on-resistance (0.25Ω typ). To
minimize radiated noise in sensitive applications, use a
shielded inductor.
READY
> V
> V
> V
GATE
ONDC
ONP
ONN
ON2
LAVG
P
LR
I



PEAK
2
1
=
is the average inductor current and R



I
LAVG



V
=
IN(MIN)
V
GATE
ENABLES REG 1 LINEAR-REGULATOR
ENABLES REG 2 LINEAR-REGULATOR
ENABLES STEP-UP REGULATOR
ENABLES REG P LINEAR-REGULATOR
ENABLES REG N LINEAR-REGULATOR



MAIN
2
I
MAIN(MAX) MAIN
R
L
≅
V



IN(MIN)






I
MAIN
V
MAIN
V
V
Lf
×
IN
V
- V
OSC
MAIN
IN(MIN)






1
η




 +

2
R



L
LR
), which
L
21
is