BELLING BL2046QN Temperature measurement Datasheet

BL2046
Low Voltage I/O TOUCH SCREEN CONTROLLER
Features
2.2V to 5.25V operation
1.5V to 5.25V digital I/O
Internal 2.5V reference
4-wire I/F
Programmable 8 or 12 bit Resolution
Direct battery measurement(0V to 6V)
Temperature measurement
Touch-pressure measurement
Available in QFN-16 and TSSOP-16 package
General Description
The BL2046 is a 4-wire touch screen controller which supports a low-voltage I/O interface from
1.5V to 5.25V. The BL2046 has an on-chip 2.5V reference that can be used for the auxiliary input,
battery monitor, and temperature measurement modes. The reference can also be powered down
when not used to conserve power. The internal reference operates down to 2.7V supply voltage,
while monitoring the battery voltage from 0V to 6V.
The BL2046 is a highly integrated controller for portable applications with 4-wire resistive touch
panel such as, PDA, portable instruments, cellular phone, etc.
Applications
Cellular phones
Personal digital assistants
Touch screen monitors
Portable instruments
Order Information
Part Number
Package
Shipping
BL2046QN
QFN-16
3000pcs / Tape & Reel
BL2046TS
TSSOP-16
2500pcs / Tape & Reel
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BL2046
Absolute Maximum Ratings
+VCC and IOVDD to GND…………………………………………….. –0.3V to +6V
Analog Inputs to GND…………………………………………. –0.3V to +VCC + 0.3V
Digital Inputs to GND ……………………………………… –0.3V to IOVDD + 0.3V
Power Dissipation ……………………………………………………………..250mW
Maximum Junction Temperature……………………………………………... +150°C
Operating Temperature Range ……………………………………….–40°C to +85°C
Storage Temperature Range………………………………………… –65°C to +150°C
Lead Temperature (soldering, 10s) ……………………………………………+300°C
Pin Diagrams
2046A - product code
Y - assembly year
WW - assembly week
SSSS - digits from lot number
Pin Description
No.
Pin Name
1
BUSY
2
DIN
3
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Description
Busy Output. This output is high impedance when
Serial Data Input. If
DCLK.
is high.
is low, data is latched on rising edge of
Chip Select Input. Controls conversion timing and enables the serial
input/output register.
high = power-down mode (ADC only).
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BL2046
4
DCLK
External Clock Input. This clock runs the SAR conversion process
and synchronizes serial data I/O.
5
+Vcc
Power Supply
6
X+
X+ Position Input
7
Y+
Y+ Position Input
8
X-
X– Position Input
9
Y-
Y– Position Input
10
GND
Ground
11
VBAT
Battery Monitor Input
12
AUX
Auxiliary Input to ADC
13
VREF
Voltage Reference Input/Output
14
IOVDD
Digital I/O Power Supply
15
16
Pen Interrupt
DOUT
Serial Data Output. Data is shifted on the falling edge of DCLK.
This output is high impedance when
is high.
Typical Application Circuit
Figure 1 Typical Application Circuit of the BL2046
Electrical Characteristics
At TA = –40°C to +85°C, +VCC = +2.7V, VREF = 2.5V internal voltage, fSAMPLE = 125kHz, fCLK =
16 • fSAMPLE = 2MHz, 12-bit mode, digital inputs = GND or IOVDD, and +VCC must be •IOVDD,
unless otherwise noted
PARAMETER
CONDITIONS
BL2046
MIN
REFERENCE OUTPUT
2.46
Internal Reference Voltage
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TYP
MAX
2.54
250
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UNITS
V
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BL2046
Internal Reference Drift
15
ppm/℃
Quiescent Current
500
uA
ANALOG INPUT
Full-Scale Input Span
Absolute Input Range
Positive Input-Negative Input
0
VREF
V
Positive Input
-0.2
+VCC+0.2
V
Negative Input
-0.2
+0.2
V
Capacitance
25
PF
Leakage Current
0.1
uA
TEMPERATURE
MEASUREMENT
Temperature Range
Resolution
Accuracy
-40℃
+85
3
Differential Method
TEMPO:
4
3
Differential Method
4
TEMPO
℃
1.6
℃
0.3
℃
±2
℃
±3
℃
SYSTEM PERFORMANCE
Resolution
12
No Missing Codes
Bits
11
Bits
Integral Linearity Error
±2
LSB1
Offset Error
±6
LSB
±4
LSB
Gain Error
Noise
External VREF
Including Internal VREF
Power-Supply Rejection
70
uVrms
70
dB
SAMPLING DYNAMICS
Conversion Time
12
Acquisition Time
CLKCycles
3
CLKCycles
Throughput Rate
125
Multiplexer Settling Time
khz
500
ns
Aperture Delay
30
ns
Aperture Jitter
100
ps
100
dB
Channel-to-Channel Isolation
VIN = 2.5Vp-p at 50kHz
BATTERY MONITOR
Input Voltage Range
0.5
6.0
V
Input Impedance
Sampling Battery
10
kΩ
Battery Monitor Off
1
GΩ
Accuracy
VBAT = 0.5V to 5.5V, External
VREF =2.5V
-2
+2
%
-3
+3
%
VBAT = 0.5V to 5.5V,
Internal Reference
REFERENCE INPUT
1.0
+VCC
Range
Input Impedance
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V
SER/DFR = D, PD1 = 0,
Internal Reference Off
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GΩ
1
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BL2046
Internal Reference On
250
Ω
DIGITAL INPUTfOUTPUT
Logic Family
CMOS
VIH
I︱IH︱≤+5uA
VIL
I︱IL︱≤+5uA
VOH
LOH = -250 uA
VOL
LOL = 250uA
IOVDD·0.7
-0.3
IOVDD+0.3
V
0.3 • IOVDD
V
V
IOVDD·0.8
Data Format
0.4
V
Straight
Binary
POWER-SUPPLY
REQUIREMENTS
+VCC5
Specified Performance
2.7
3.6
V
Operating Range
2.2
5.25
V
1.5
+VCC
V
650
uA
6
IOVDO
Quiescent Current
7
Internal Reference Off
280
Internal Reference On
780
uA
220
uA
fSAMPLE= 12.5kHz
Power-Down Mode with
3
uA
1.8
mW
+85
℃
CS=DCLK=DIN=IOVDD
Power Dissipation
+VCC=+2.7V
TEMPERATURE RANGE
Specified Performance
-40
SWITCH DRIVERS
Qn-Resistance
Y+, X+
Y-.XDrive Current
2
Duration 100ms
5
Ω
6
Ω
50
NOTES: (1) LSB means least significant bit. With VREF = +2.5V, one LSB is 610µV. (2) Assured by design, but
not tested. Exceeding 50mA source current may result in device degradation. (3) Difference between TEMP0 and
TEMP1 measurement, no calibration necessary. (4) Temperature drift is –2.1mV/°C. (5) BL2046 operates down to
2.2V. (6) IOVDD must be - +VCC. (7) Combined supply current from +VCC and IOVDD. Typical values obtained
from conversions on AUX input with PD0 = 0.
Analog Input
Table 1 and Table 2 show the relationship between the A2, A1, A0, and SER/
control bits
and the configuration of the BL2046. The control bits are provided serially via the DIN pin (see
the Digital Interface section of this data sheet for more details).
When the converter enters the hold mode, the voltage difference between the +IN and –IN inputs
is captured on the internal capacitor array. The input current into the analog inputs depends on the
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mA
BL2046
conversion rate of the device. During the sample period, the source must charge the internal
sampling capacitor . After the capacitor has been fully charged, there is no further input current.
The rate of charge transfer from the analog source to the converter is a function of conversion rate.
TABLE 1. Input Configuration (DIN), Single-Ended Reference Mode (SER/
TABLE 2. Input Configuration (DIN), Differential Reference Mode (SER/
high).
low).
Internal Reference
The BL2046 has an internal 2.5V voltage reference that can be turned on or off with the control bit,
PD1 (see Table 5 ). Typically, the internal reference voltage is only used in the single-ended mode
for battery monitoring, temperature measurement, and for using the auxiliary input. Optimal touch
screen performance is achieved when using the differential mode.
Reference Input
The voltage difference between +REF and –REF sets the analog input range. The BL2046
operates with a reference in the range of 1V to +VCC. There are several critical items concerning
the reference input and its wide voltage range. As the reference voltage is reduced, the analog
voltage weight of each digital output code is also reduced. This is often referred to as the LSB
size and is equal to the reference voltage divided by 4096 in 12-bit mode. Any offset or gain error
inherent in the ADC appears to increase, in terms of LSB size, as the reference voltage is reduced.
With a lower reference voltage, more care must be taken to provide a clean layout including
adequate bypassing, a clean power supply, a low-noise reference, and a low-noise input signal.
The voltage into the VREF input directly drives the capacitor digital-to-analog converter (CDAC)
portion of the BL2046. Therefore, the input current is very low.
There is also a critical item regarding the reference when making measurements while the switch
drivers are ON. For this discussion, it is useful to consider the typical application of the BL2046.
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BL2046
This particular application shows the device being used to digitize a resistive touch screen. A
measurement of the current Y-Position of the pointing device is made by connecting the X+ input
to the ADC, turning on the Y+ and Y– drivers, and digitizing the voltage on X+. For this
measurement, the resistance in the X+ lead does not affect the conversion. However, since the
resistance between Y+ and Y– is fairly low, the on-resistance of the Y drivers does make a small
difference. Under the situation outlined so far, it is not possible to achieve a 0V input or a
full-scale input regardless of where the pointing device is on the touch screen because some
voltage is lost across the internal switches. In addition, the internal switch resistance is unlikely to
track the resistance of the touch screen, providing an additional source of error.
Figure 2. Diagram of Single-Ended Reference (SER/
analog input).
high, Y switches enabled, X+ is
This situation can be remedied (see Figure 3) . By setting the SER/
bit low, the +REF and
–REF inputs are connected directly to Y+ and Y–, respectively, which makes the analog-to-digital
conversion ratiometric. The result of the conversion is always a percentage of the external
resistance, regardless of how it changes in relation to the on-resistance of the internal switches.
Note that there is an important consideration regarding power dissipation when using the
ratiometric mode of operation.
As a final note about the differential reference mode, it must be used with +VCC as the source of
the +REF voltage and cannot be used with VREF. It is possible to use a high-precision reference on
VREF and single-ended reference mode for measurements which do not need to be ratiometric. In
some cases, it is possible to power the converter directly from a precision reference. Most
references can provide enough power for the BL2046, but might not be able to supply enough
current for the external load (such as a resistive touch screen).
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BL2046
Figure 3. Diagram of Differential Reference (SER/
analog input).
low, Y switches enabled, X+ is
Touch Screen Setting
In some applications, external capacitors may be required across the touch screen for filtering
noise picked up by the touch screen. These capacitors provide a low-pass filter to reduce the noise,
but cause a settling time requirement when the panel is touched that typically shows up as a gain
error. There are several methods for minimizing or eliminating this issue. The problem is the input
and/or reference has not settled to the final steady-state value prior to the ADC sampling the
input(s) and providing the digital output. Additionally, the reference voltage may still be changing
during the measurement cycle. Option 1 is to stop or slow down the BL2046 DCLK for the
required touch screen settling time. This allows the input and reference to have stable values for
the Acquire period (3 clock cycles of the BL2046; see Figure 7). This works for both the
single-ended and the differential modes. Option 2 is to operate the BL2046 in the differential
mode only for the touch screen measurements and command the BL2046 to remain on (touch
screen drivers ON) and not go into power-down (PD0 = 1). Several conversions are made
depending on the settling time required and the BL2046 data rate. Once the required number of
conversions have been made, the processor commands the BL2046 to go into its power-down state
on the last measurement. This process is required for X-Position, Y-Position, and Z-Position
measurements. Option 3 is to operate in the 15 Clock-per-Conversion mode, which overlaps the
analog-to-digital conversions and maintains the touch screen drivers on until commanded to stop
by the processor (see Figure 11).
Tempeature Mesurement
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BL2046
In some applications, such as battery recharging, a measurement of ambient temperature is
required. The temperature measurement technique used in the BL2046 relies on the characteristics
of a semiconductor junction operating at a fixed current level. The forward diode voltage (VBE)
has a well-defined characteristic versus temperature. The ambient temperature can be predicted in
applications by knowing the +25°C value of the VBE voltage and then monitoring the delta of that
voltage as the temperature changes. The BL2046 offers two modes of operation. The first mode
requires calibration at a known temperature, but only requires a single reading to predict the
ambient temperature. A diode is used (turned on) during this measurement cycle. The voltage
across the diode is connected through the MUX for digitizing the forward bias voltage by the
ADC with an address of A2 = 0, A1 = 0, and A0 = 0 (see Table 1 and Figure 4 for details). This
voltage is typically 600mV at +25°C with a 20µA current through the diode. The absolute value of
this diode voltage can vary a few millivolts. However, the TC of this voltage is very consistent at
–2.1mV/°C. During the final test of the end product, the diode voltage would be stored at a
known room temperature, in memory, for calibration purposes by the user. The result is an
equivalent temperature measurement resolution of 0.3°C/LSB (in 12-bit mode).
Figure 4. Functional Block Diagram of Temperature Measurement Mode.
The second mode does not require a test temperature calibration, but uses a two-measurement
method to eliminate the need for absolute temperature calibration and for achieving 2°C accuracy.
This mode requires a second conversion with an address of A2 = 1, A1 = 1, and A0 = 1, with a 91
times larger current. The voltage difference between the first and second conversion using 91
times the bias current is represented by kT/q • ln (N), where N is the current ratio = 91, k =
Boltzmann’s constant (1.38054 • 10–23 electron volts/ degrees Kelvin), q = the electron charge
(1.602189 • 10–19 C), and T = the temperature in degrees Kelvin. This method can provide
improved absolute temperature measurement over the first mode at the cost of less resolution
(1.6°C/LSB). The equation for solving for °K is:
where,
°K = q • △V/(k • ln (N))
V = V (I91) – V (I1) (in mV)
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BL2046
∴°K = 2.573 °K/mV • △V
°C = 2.573 •△V(mV) – 273°K
NOTE: The bias current for each diode temperature measurement is only on for 3 clock cycles
(during the acquisition mode) and, therefore, does not add any noticeable increase in power,
especially if the temperature measurement only occurs occasionally.
Battery Mesruement
An added feature of the BL2046 is the ability to monitor the battery voltage on the other side of
the voltage regulator (DC/DC converter), as shown in Figure 5. The battery voltage can vary from
0V to 6V, while maintaining the voltage to the BL2046 at 2.7V, 3.3V, etc. The input voltage
(VBAT) is divided down by 4 so that a 5.5V battery voltage is represented as 1.375V to the ADC.
This simplifies the multiplexer and control logic. In order to minimize the power consumption, the
divider is only on during the sampling period when A2 = 0, A1 = 1, and A0 = 0 (see Table 1 for
the relationship between the control bits and configuration of the BL2046).
Figure 5. Battery Measurement Functional Block Diagram.
Pressure Mesurement
Measuring touch pressure can also be done with the BL2046. To determine pen or finger touch,
the pressure of the touch needs to be determined. Generally, it is not necessary to have very high
performance for this test, therefore, the 8-bit resolution mode is recommended (however,
calculations will be shown here in the 12-bit resolution mode). There are several different ways of
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BL2046
performing this measurement. The BL2046 supports two methods. The first method requires
knowing the X-plate resistance, measurement of the X-Position, and two additional cross panel
measurements (Z1 and Z2) of the touch screen, as shown in Figure 6. Using Equation 2 calculates
the touch resistance:
The second method requires knowing both the X-plate and Y-plate resistance, measurement of
X-Position and Y-Position, and Z1. Using Equation 3 also calculates the touch resistance:
Figure 6. Pressure Measurement Block Diagrams.
Digital Interface
Figure 7 shows the typical operation of the BL2046 digital interface. This diagram assumes that
the source of the digital signals is a microcontroller or digital signal processor with a basic serial
interface. Each communication between the processor and the converter, such as SPI or SSI
synchronous serial interface, consists of eight clock cycles. One complete conversion can be
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BL2046
accomplished with three serial communications for a total of 24 clock cycles on the DCLK input.
The first eight clock cycles are used to provide the control byte via the DIN pin. When the
converter has enough information about the following conversion to set the input multiplexer and
reference inputs appropriately, the converter enters the acquisition (sample) mode and, if needed,
the touch panel drivers are turned on. After three more clock cycles, the control byte is complete
and the converter enters the conversion mode. At this point, the input sample-and-hold goes into
the hold mode and the touch panel drivers turn off (in single-ended mode). The next 12 clock
cycles accomplish the actual analog-to-digital conversion. If the conversion is ratiometric
(SER/
= 0), the drivers are on during the conversion and a 13th clock cycle is needed for the
last bit of the conversion result. Three more clock cycles are needed to complete the last byte
(DOUT will be low), which are ignored by the converter.
Control Byte
The control byte (on DIN), as shown in Table 3, provides the start conversion, addressing, ADC
resolution, configuration, and power-down of the BL2046. Tables 3 and 4 give detailed
information regarding the order and description of these control bits within the control byte.
Bit7
(MSB)
Bit 6
Bit 5
Bit 4
Bit 3
S
A2
A1
A0
MODE
Bit 2
SER/
Bit 1
Bit 0
(LSB)
PD1
PD0
TABLE 3. Order of the Control Bits in the Control Byte.
BIT
NAME
DESCRIPTION
7
S
6-4
A2-A0
3
MODE
2
SER/
1-0
PD1-PD0
Start bit. Control byte starts with first high bit on DIN.A new control byte
can start every 15th clock cycle in 12-bit conversion mode or every 11th
clock cycle in 8-bit conversion mode (see Figure 11).
Channel Select bits. Along with the SER/
bit, these bits control the
setting of the multiplexer input, touch driver switches, and reference inputs
(see Tables 1 and 2).
12-Bit/8-Bit Conversion Select bit. This bit controls the number of bits for
the next conversion: 12-bits (low) or 8-bits (high).
Single-Ended/Differential Reference Select bit. Along with bits A2-A0, this
bit controls the setting of the multiplexer input, touch driver switches, and
reference
inputs (see Tables 1 and 2).
Power-Down Mode Select bits. Refer to Table V for details.
TABLE 4. Descriptions of the Control Bits within the Control Byte.
Initiate START—The first bit, the S bit, must always be high and initiates the start of the
control byte. The BL2046 ignores inputs on the DIN pin until the start bit is detected.
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BL2046
Addressing—The next three bits (A2, A1, and A0) select the active input channel(s) of the input
multiplexer (see Tables 1, 2), touch screen drivers, and the reference inputs.
MODE—The mode bit sets the resolution of the ADC. With this bit low, the next conversion has
12 bits of resolution, whereas with this bit high, the next conversion has 8 bits of resolution.
SER/
—The SER/
bit controls the reference mode, either single-ended (high) or
differential (low). The differential mode is also referred to as the ratiometric conversion mode and
is preferred for X-Position, Y-Position, and Pressure- Touch measurements for optimum
performance. The reference is derived from the voltage at the switch drivers, which is almost the
same as the voltage to the touch screen. In this case, a reference voltage is not needed as the
reference voltage to the ADC is the voltage across the touch screen. In the single-ended mode, the
converter reference voltage is always the difference between the VREF and GND pins.
If X-Position, Y-Position, and Pressure-Touch are measured in the single-ended mode, an external
reference voltage is needed. The BL2046 must also be powered from the external reference.
Caution should be observed when using the single-ended mode such that the input voltage to the
ADC does not exceed the internal reference voltage, especially if the supply voltage is greater than
2.7V.
NOTE: The differential mode can only be used for X-Position, Y-Position, and Pressure-Touch
measurements. All other measurements require the single-ended mode.
PD0 and PD1—Table 5 describes the power-down and the internal reference voltage
configurations. The internal reference voltage can be turned on or off independently of the ADC.
This can allow extra time for the internal reference voltage to settle to the final value prior to
making a conversion. Make sure to also allow this extra wake-up time if the internal reference is
powered down. The ADC requires no wake-up time and can be instantaneously used. Also note
that the status of the internal reference power-down is latched into the part (internally) with BUSY
going high. In order to turn the reference off, an additional write to the BL2046 is required after
the channel has been converted.
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BL2046
Figure 7. Conversion Timing, 24 Clocks-per-Conversion, 8-Bit Bus Interface. No DCLK delay
required with dedicated serial port.
DESCRIPTION
PD1
PD0
0
0
Enabled
0
1
Disabled
Power-Down Between Conversions. When each conversion is
finished, the converter enters a low-power mode. At the start of
the next conversion, the device instantly powers up to full power.
There is no need for additional delays to ensure full operation,
and the very first conversion is valid. The Y– switch is on when
in power-down.
Reference is off and ADC is on.
1
0
Enabled
Reference is on and ADC is off.
1
1
Disabled
Device is always powered. Reference is on andADC is ON.
TABLE 5. Power-Down and Internal Reference Selection.
OUTPUT
The pen-interrupt output function is shown in Figure 8. While in power-down mode with PD0 = 0,
output is
the Y– driver is on and connects the Y-plane of the touch screen to GND. The
connected to the X+ input through two transmission gates. When the screen is touched, the X+
input is pulled to ground through the touch screen.
In most of the BL2046 models, the internal pullup resistor value is nominally 50kΩ, but this may
vary between 36K and 67kΩ given process and temperature variations. In order to assure a logic
low of 0.35VDD is presented to the
terminals must be less than 21kΩ.
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circuitry, the total resistance between the X+ and Y- 14 -
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BL2046
The -90 version of the BL2046 uses a nominal 90kΩ pullup resistor, which allows the total
resistance between the X+ and Y- terminals to be as high as 30kΩ. Note that the higher pullup
resistance will cause a slower response time of the
should take this into account.
to a screen touch, so user software
The
output goes low due to the current path through the touch screen to ground, which
initiates an interrupt to the processor. During the measurement cycle for X-, Y-, and Z-Position,
the X+ input is disconnected from the
internal pull-up resistor. This is done to eliminate
any leakage current from the internal pull-up resistor through the touch screen, thus causing no
errors.
Figure 8.
Functional Block Diagram.
Furthermore, the
output is disabled and low during the measurement cycle for X-, Y-,
and Z-Position. The
output is disabled and high during the measurement cycle for battery
monitor, auxiliary input, and chip temperature. If the last control byte written to the BL2046
contains PD0 = 1, the pen-interrupt output function is disabled and is not able to detect when the
screen is touched. In order to re-enable the pen-interrupt output function under these
circumstances, a control byte needs to be written to the BL2046 with PD0 = 0. If the last control
byte written to the BL2046 contains PD0 = 0, the pen-interrupt output function is enabled at the
end of the conversion. The end of the conversion occurs on the falling edge of DCLK after bit 1 of
the converted data is clocked out of the BL2046.
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BL2046
is associated with whenever the
It is recommended that the processor mask the interrupt
processor sends a control byte to the BL2046. This prevents false triggering of interrupts when the
output is disabled in the cases discussed in this section.
Figure 9. Conversion Timing, 16 Clocks-per-Conversion, 8-Bit Bus Interface. No DCLK delay
required with dedicated serial port.
16 Clocks-per-Conversion
The control bits for conversion n + 1 can be overlapped with conversion n to allow for a
conversion every 16 clock cycles, as shown in Figure 9. This figure also shows possible serial
communication occurring with other serial peripherals between each byte transfer from the
processor to the converter. This is possible, provided that each conversion completes within 1.6ms
of starting. Otherwise, the signal that is captured on the input sample-and-hold may droop enough
to affect the conversion result. Note that the BL2046 is fully powered while other serial
communications are taking place during a conversion.
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BL2046
TABLE 6. Timing Specifications, TA = –40°C to +85°C.
Figure 10. Detailed Timing Diagram.
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BL2046
Figure 11. Maximum Conversion Rate, 15 Clocks-per-Conversion.
Digital Timing
Figures 7 and 10 and Table 6 provide detailed timing for the digital interface of the BL2046.
15 Clocks-per-Conversion
Figure 12. Ideal Input Voltages and Output Codes.
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BL2046
Figure 11 provides the fastest way to clock the BL2046. This method does not work with the serial
interface of most microcontrollers and digital signal processors, as they are generally not capable
of providing 15 clock cycles per serial transfer. However, this method can be used with field
programmable gate arrays (FPGAs) or application specific integrated circuits (ASICs). Note that
this effectively increases the maximum conversion rate of the converter beyond the values given
in the specification tables, which assume 16 clock cycles per conversion.
Data Format
The BL2046 output data is in Straight Binary format, as shown in Figure 12. This figure shows the
ideal output code for the given input voltage and does not include the effects of offset, gain, or
noise.
8-Bit Conversion
The BL2046 provides an 8-bit conversion mode that can be used when faster throughput is needed
and the digital result is not as critical. By switching to the 8-bit mode, a conversion is complete
four clock cycles earlier. Not only does this shorten each conversion by four bits (25% faster
throughput), but each conversion can actually occur at a faster clock rate. This is because the
internal settling time of the BL2046 is not as critical—settling to better than 8 bits is all that is
needed. The clock rate can be as much as 50% faster. The faster clock rate and fewer clock cycles
combine to provide a 2x increase in conversion rate.
Power Dissipation
There are two major power modes for the BL2046: full-power (PD0 = 1) and auto power-down
(PD0 = 0). When operating at full speed and 16 clocks-per-conversion (see Figure 9), the BL2046
spends most of the time acquiring or converting. There is little time for auto power-down,
assuming that this mode is active. Therefore, the difference between full-power mode and auto
power-down is negligible. If the conversion rate is decreased by slowing the frequency of the
DCLK input, the two modes remain approximately equal. However, if the DCLK frequency is
kept at the maximum rate during a conversion but conversions are done less often, the difference
between the two modes is dramatic.
also puts the BL2046 into power-down mode. When
goes high, the BL2046 immediately
goes into power-down mode and does not complete the current conversion. The internal reference,
going high. To turn the reference off, an additional write is
however, does not turn off with
required before
goes high (PD1 = 0).
When the BL2046 first powers up, the device draws about 20µA of current until a control byte is
written to it with PD0 = 0 to put it into power-down mode. This can be avoided if the BL2046 is
powered up with
= 0 and DCLK = IOVDD.
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Total 19 Pages
BL2046
Package Dimensions
QFN-16
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BL2046
TSSOP-16
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