Datasheet
FUNCTIONAL OVERVIEW
TPS65820
SLVS663B – MAY 2006 – REVISED APRIL 2008 ..............................................................................................................................................................
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Table 12. ADC Input Channel Oerview
Voltage Range Under Full Scale Reading
LSB
Channel Connection Parameter Sampled Normal Operating Special Features (Internal reference
Value
Conditions selected )
CH1 ANLG1 pin User defined User defined Internal pullup current 2.535 V Full-scale
source programmable reading
CH2 ANLG2 pin 2.535 V
via I
2
C : 0/10/50/60 µ A ÷ 1023
CH3 ISET1 pin Voltage proportional to 0 V (charger off) to — 2.535 V
charge current 2.525 V (fast charge)
CH4 TS pin Voltage proportional to pack 0 V (short) to 4.7 V (no Internal 20- µ A pullup 2.535 V
temperature thermistor) current source (ON
only when AC/USB
are present)
CH5 Internal Voltage proportional to IC 1.85 V at T
J
= 25 ° C, — 2.535 V
junction junction temperature – 6.5 mV/ ° C slope typ
temperature
CH6 RTC_OUT Internal LDO output voltage 0 V to 3.3 V — 4.7 V
pin
CH7 OUT pin System power bus voltage 0 V to 4.4 V — 4.7 V
CH8 BAT pin Battery pack positive 0 V to 4.4 V — 4.7 V
terminal voltage
The TPS65820 ADC can be subdivided in four sections:
1. Input selection: The input selection section has two major blocks, the input bias control and an 8 channel
MUX. The input bias control provides the bias currents that are applied to pins ANLG1 and ANLG2 and pin
TS. The TS pin bias current is fixed (20 µ A typ), and the bias currents for pins ANLG1 and ANLG2 are set on
I
2
C register ADC_WAIT.
The TS and ANLG1 pin current sources are automatically enabled when the input power is detected,
providing the required setup to measure a pack thermistor temperature (TS pin) or a battery ID resistor
(ANLG1 pin). ANLG1 and ANLG2 can be used to measure external resistive loads or analog voltages. The
bias current sources are always connected to the OUT pin internally.
The internal MUX connects one of the monitored analog inputs to the ADC engine, following the selection
defined on register ADC_SET.
2. ADC engine: The ADC engine uses an internal or external voltage reference, as defined by the ADC_REF
bit on the ADC_SET control register. If the internal reference is selected ADC_REF is connected to an
internal LDO that regulates the ADC_REF pin voltage to generate the ADC supply and internal voltage
reference. The internal LDO maximum output current is 6 mA typical, and a conversion should be started
only after the external capacitor is fully charged.
If an external reference is used it should be connected to the ADC_REF pin. When an external reference is
selected the internal LDO connected to ADC_REF is disabled. Care must be taken when selecting an
external reference as the ADC reference voltage, as it affects the ADC LSB absolute value.
3. Trigger control and synchronization : The ADC engine starts a conversion of the selected input when the
trigger control circuit sends a start command. The trigger control circuit starts the ADC conversion and
transfers the ADC output data to the arithmetic logic unit (ALU) at the end of the conversion. It also
synchronizes the data transfer from the ALU to the I
2
C ADC_READING register at the end of a conversion
cycle, and generates the ADC status information sent to the ADC registers.
An ADC engine conversion is triggered by the TPS65820 trigger control circuit using either an internal trigger
or an external trigger. The internal trigger is automatically generated by the TPS65820 at the end of each
ADC engine conversion, following the timing parameters set on I
2
C registers ADC_SET, ADC_DELAY and
ADC_WAIT.
The GPIO3 pin can be used as an external trigger if the bit ADC_TRG_GPIO3 is set HI, in the I
2
C register
ADC_DELAY. In the external trigger mode a new conversion is started after the GPIO3 pin has an edge
transition, following the timing parameters set on I
2
C registers ADC_SET, ADC_DELAY and ADC_WAIT.
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