isppac-powr1220at8 Lattice Semiconductor Corp., isppac-powr1220at8 Datasheet - Page 20

• Manufacturer Part Number: isppac-powr1220at8
• Description: In-system Programmable Power Supply Monitoring, Sequencing And Margining Controller
• Manufacturer: Lattice Semiconductor Corp.

Lattice Semiconductor
VMON Voltage Measurement with the On-chip Analog to Digital Converter (ADC)
The ispPAC-POWR1220 has an on-chip analog to digital converter that can be used for measuring the voltages at
the VMON inputs. The ADC is also used in closed loop trimming of DC-DC converters. Close loop trimming is cov-
ered later in this document.
Figure 1-9. ADC Monitoring VMON1 to VMON12
Figure 1-9 shows the ADC circuit arrangement within the ispPAC-POWR1220AT8 device. The ADC can measure
all analog input voltages through the multiplexer, ADC MUX. The programmable attenuator between the ADC mux
and the ADC can be configured as divided-by-3 or divided-by-1 (no attenuation). The divided-by-3 setting is used to
measure voltages from 0V to 6V range and divided-by-1 setting is used to measure the voltages from 0V to 2V
range.
A microcontroller can place a request for any VMON voltage measurement at any time through the I
the receipt of an I
ADC output is then latched into the I
Calculation
The algorithm to convert the ADC code to the corresponding voltage takes into consideration the attenuation bit
value. In other words, if the attenuation bit is set, then the 10-bit ADC result is automatically multiplied by 3 to cal-
culate the actual voltage at that V
formula can always be used to calculate the actual voltage from the ADC code.
Voltage at the VMONx Pins
1
Note: ADC_VALUE_HIGH (8 bits), ADC_VALUE_LOW (4 bits) read from I
VMON = ADC code (12 bits
VMON12
VDDINP
VMON1
VMON2
VMON3
VDDA
2
C command, the ADC will be connected to the I
From Closed
Loop Trim
ADC
MUX
Circuit
1
, converted to decimal) * 2mV
MON
4
5
2
C readout registers.
input. Thus, the I
Programmable
5
ADC MUX
Attenuator
From I
Register
Analog
3
2
5
1
C
1
Control Signal
2
1-20
C readout register is 12 bits instead of 10 bits. The following
Internal
2
C/SMBUS interface
ADC
Internal
2.048V
VREF-
2
C selected VMON through the ADC MUX. The
ispPAC-POWR1220AT8 Data Sheet
10
Programmable
Multiplier
Digital
3
1
12
To Closed
Loop Trim
Readout
Register
To I
Circuit
2
C bus. Upon
2
C