ISL45042_14 Datasheet, PDF (6/9 Pages) Intersil Corporation – LCD Module Calibrator

ISL45042
Expected Output Voltage
The ISL45042 provides an output sink current, which lowers
the voltage on the external voltage divider (V_COM output
voltage). Equations 1 and 2 can be used to calculate the
output current (I_OUT) and output voltage (V_OUT) values.
I_OUT
=
S_-----e_----t_--t_--i_--n_----g_-
128
x
-₂---₀--^A--₍--_RV-----_SD----_ED---_T----₎
(EQ. 1)
V_OUT
=
⎛
⎜
⎝
-_R----₁--^R---+--²--_R-----₂-_{⎠⎟⎞}
A
V_D
⎛
D _⎝⎜
1
–
S_-----e_----t_--t_--i_--n_----g_-
128
x
-₂---₀----₍--_R-^R----_S1----_E---_T----_{)⎠⎟⎞}
(EQ. 2)
(Where “Setting” is an integer between 1 and 128.)
1kΩ
0.01µF
ISL45042
CTL
FIGURE 3. EXTERNAL ESD PROTECTION ON CTL PIN
Table 1 gives the calculated value of V_OUT for resistors
values of: R_SET = 24.9kΩ, R₁ = 200kΩ, R₂ = 243kΩ, and
AV_DD = 10V.
TABLE 1. CALCULATED VCOM OUTPUT VOLTAGES
SETTING VALUE
1
V_OUT
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
TABLE 1. CALCULATED VCOM OUTPUT VOLTAGES
SETTING VALUE
90
V_OUT
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 (see Figure 1). The voltage difference between the
V_OUT pin and I_SET pin (see Figure 5) has to be greater than
1.75V. This will keep the output MOS transistor in the saturation
region. Expected current settings and 7-bit accuracy occurs
when the output MOS transistor is operating in the saturation
region. Figure 5 shows the internal connection for the output
MOS transistor. The value of the AV_DD supply sets the voltage
at the source of the output transistor. This voltage is equal to
(Setting/128) x (AV_DD/20). The I_SET current is therefore equal
to (Setting/128) x (AV_DD/20 x R_SET). The value of the Drain
voltage is found using Equation 2. The values of R₁ and R₂ in
Equation 2, should be determined (setting equal to 128) so the
minimum value of V_OUT is greater than 1.75V + AV_DD/20.
S-----E----T-----T----I--N-----G--- _x ^{A-----V-----D----D---}
128
20
VOUT PIN ^{AVDD = 15V}
R1
AVDD
VSAT
R2
0.5V
RSET
ISET PIN
FIGURE 5. OUTPUT CONNECTION CIRCUIT EXAMPLE
AVDD
R_a
-
R_b
+
R_c
VCOM
R₁ = R_a
R₂ = R_b + R_c
AVDD
AVDD
ISL45042
SET
OUT
R_SET
R₁
-
+
R₂
VCOM
R_SET = (R_a(R_b + Rc)) / 20R_b
FIGURE 4. EXAMPLE OF THE REPLACEMENT FOR THE MECHANICAL POTENTIOMETER CIRCUIT USING THE ISL45042
6
FN6072.9
April 13, 2011