Datasheet

MAX17094
Internal-Switch Boost Regulator with Integrated
7-Channel Driver, VCOM Calibrator, Op Amp, and LDO
22 ______________________________________________________________________________________
Input-Voltage Detector
The falling-edge input-voltage threshold used by the volt-
age detector to drive YDCHG to VGON1 during power-
down is adjusted by connecting a resistive voltage-
divider from V
IN
to AGND with the center tap connected
to SENSE (see Figure 2). Select R6 in the 10kΩ range.
Calculate R5 with the following equation:
Setting the VCOM Adjustment Range
The external resistive voltage-divider sets the maximum
value of the VCOM adjustment range. R
SET
sets the full-
scale sink current, I
OUT
, which determines the minimum
value of the VCOM adjustment range. Large R
SET
val-
ues increase resolution but decrease the VCOM adjust-
ment range. Calculate R3, R4, and R
SET
using the
following procedure:
1) Choose the maximum VCOM level (V
MAX
), the mini-
mum VCOM level (V
MIN
), and the AVDD supply
voltage (V
AVDD
).
2) Select R3 between 10kΩ and 500kΩ based on the
acceptable power loss from the V
MAIN
supply rail
connected to AVDD.
3) Calculate R4:
4) Calculate R
SET
:
5) Verify that I
SET
does not exceed 120μA:
6) If I
SET
exceeds 120μA, return to step 2 and choose
a larger value for R1.
The resulting resolution is:
A complete design example is given below:
V
MAX
= 4V, V
MIN
= 2.4V, V
MAIN
= 8V
If R3 = 200kΩ, then R4 = 200kΩ and R
SET
= 24.9kΩ.
Resolution = 12.5mV
Applications Information
Power Dissipation
An IC’s maximum power dissipation depends on the
thermal resistance from the die to the ambient environ-
ment and the ambient temperature. The thermal resis-
tance depends on the IC package, PCB copper area,
other thermal mass, and airflow.
The MAX17094, with its exposed backside paddle sol-
dered to 1in
2
of PCB copper, can dissipate about
2222mW into +70°C still air. More PCB copper, cooler
ambient air, and more airflow increase the possible dis-
sipation, while less copper or warmer air decreases the
IC’s dissipation capability. The major components of
power dissipation are the power dissipated in the step-
up regulator and the power dissipated by the opera-
tional amplifiers.
The MAX17094’s largest on-chip power dissipation
occurs in the step-up switch, the VCOM amplifiers, the
LDO, and the high-voltage scan driver outputs.
Step-Up Regulator
The largest portions of the power dissipated by the
step-up regulator are the internal MOSFET, the induc-
tor, and the output diode. If the step-up regulator with
3.3V input and 300mA output has approximately 85%
efficiency, approximately 5% of the power is lost in the
internal MOSFET, approximately 3% in the inductor,
and approximately 5% in the output diode. The remain-
ing few percent are distributed among the input and
output capacitors and the PCB traces. If the input
power is approximately 3W, the power lost in the inter-
nal MOSFET is approximately 150mW.
Operational Amplifiers
The power dissipated in the operational amplifiers
depends on the output current, the output voltage, and
the supply voltage:
where I
VCOM_SOURCE
is the output current sourced by
one operational amplifier, and I
VCOM_SINK
is the output
current that the operational amplifier sinks.
In a typical case where the supply voltage is 8V and the
output voltage is 4V with an output source current of
30mA for each of the four operational amplifiers, the
power dissipated is 480mW.
PD I V V
PD
SOURCE VCOM SOURCE AVDD VCOM
SINK
=×
()
=
_
-
IIV
VCOM SINK VCOM_
×
(V - V
127
MAX MIN
)
I
SET
AVDD
=
×
V
20 R
SET
RR
SET
=
×
×
V
20 (V - V
MAX
MAX MIN
)
3
RR43≅
()
×
V
V-V
MAX
AVDD MAX
RR56 1=×
⎛
⎝
⎜
⎞
⎠
⎟
V
1.235V
IN(THRESHOLD)
-