ISL45042_06 Datasheet, PDF (6/8 Pages) Intersil Corporation – LCD Module Calibrator

ISL45042
Table 1 gives the calculated value of VOUT for resistors
values of: R_SET = 24.9kΩ, R1 = 200kΩ, R2 = 243kΩ, and
V_ADD = 10V.
TABLE 1. CALCULATED VCOM OUTPUT VOLTAGES
SETTING VALUE
VOUT
1
5.468
10
5.313
20
5.141
30
4.969
40
4.797
50
4.625
60
4.453
70
4.281
80
4.109
90
3.936
100
3.764
110
3.592
128
3.282
R_SET Resistor
The external R_SET resistor sets the full-scale sink current
that determines the lowest voltage of the external voltage
divider R₁ and R₂ (Figure 1). The maximum I_SET current has
to be less than 120μA. The minimum R_SET resistor with
A_VDD equal to 10V is 4.17kΩ (10V/(20*120μA). Typical
applications with A_VDD equal to 10V and R_SET equal to
24.9kΩ will result in a set current equal to 20μA.
Power Supply Sequence
The recommendation for power supply sequence would be
to power down the part first (Vdd, AVdd), after 100msec if
programming has occurred, and then power down the
control power supplies (CTL, CE).
Verifying the Programmed Value
The following sequence can be used to verify the
programmed value without having to sequence the V_DD
supply. To verify the programmed value, follow the steps
below. The ISL45042 will read memory contents and be set
to that value when the CE pin is grounded.
1. Power up the ISL45042.
2. CE pin = V_DD.
3. Change counter value with CTL pin to desired value.
4. CTL = more than 4.9V and 200msec. Counter value
programmed.
5. Change the counter value with CTL pin to a different
value.
6. CE pin = Ground.
7. Check that the output value is the one programmed in
step #4.
Generating VDD and CE supply from a Larger
Voltage Source
The CE pin has an internal pull-down resistor (R_INTERNAL
Figure 5). The impedance of this resistor is 400kΩ-500kΩ. If
your design is using a resistor divider network to generate
the 3.3V supply (for both V_DD and CE to enable
programming) from a larger voltage source, the 400kΩ
(worst case) resistor needs to be taken into account as a
parallel resistance when the CE pin is connected to this
source. Another design concern is to be able to provide
enough supply current during programming. The ISL45042
draws about 2mA during this process. Recommended
resistor values are shown in Figure 5. This design will result
in an additional 0.83mA quiescent current flowing through
resistors R_A and R_B..
VCC= 5V
R_A
2kΩ
CE
VCE
R_B
4kΩ
ISL45042
CE LOGIC
R_INTERNAL = 400kΩ to 500kΩ
FIGURE 5. APPLICATION GENERATING VDD AND VCE
VOLTAGES
ISL45042 Truth Table
The ISL45042 truth table is shown in Table 2. For proper
operation the CE should be disabled (pulled low) before
powering the device down to assure that the glitches and
transients will not cause unwanted EEPROM overwriting.
TABLE 2. TRUTH TABLE
INPUT
OUTPUT
CTL
CE
VDD
OUT
ICC MEMORY
Mid to Hi Hi
VDD Increment Normal
X
Mid to Lo Hi
VDD Decrement Normal
X
X
Lo
VDD No Change Increased Read
>4.9V Hi
VDD No Change Increased Program
6
FN6072.6
November 14, 2006