ADM1169 Analog Devices, ADM1169 Datasheet - Page 23

• Manufacturer Part Number: ADM1169
• Description: Super Sequencer and Monitor with Margining Control and Non-Volatile Fault Recording
• Manufacturer: Analog Devices

Specifications of ADM1169

• # Supplies Monitored: 8
• Volt Monitoring Accuracy: 1%
• # Output Drivers: 8
• Fet Drive/enable Output: Both
• Voltage Readback: 12-bit ADC
• Supply Adj/margining: 12-bit ADC+4 DACs
• Package: 32 ld LQFP,40 ld LFCSP

SUPPLY MARGINING
OVERVIEW
It is often necessary for the system designer to adjust supplies,
either to optimize their level or force them away from nominal
values to characterize the system performance under these
conditions. This is a function typically performed during an
in-circuit test (ICT), such as when a manufacturer wants to
guarantee that a product under test functions correctly at
nominal supplies minus 10%.
OPEN-LOOP SUPPLY MARGINING
The simplest method of margining a supply is to implement an
open-loop technique (see Figure 32). A popular way to do this
is to switch extra resistors into the feedback node of a power
module, such as a dc-to-dc converter or low dropout regulator
(LDO). The extra resistor alters the voltage at the feedback or
trim node and forces the output voltage to margin up or down
by a certain amount.
The ADM1169 can perform open-loop margining for up to four
supplies. The four on-board voltage DACs (DAC1 to DAC4) can
drive into the feedback pins of the power modules to be margined.
The simplest circuit to implement this function is an attenuation
resistor that connects the DACx pin to the feedback node of a
dc-to-dc converter. When the DACx output voltage is set equal
to the feedback voltage, no current flows into the attenuation
resistor, and the dc-to-dc converter output voltage does not change.
Taking DACx above the feedback voltage forces current into the
CONVERTER
DC-TO-DC
FEEDBACK
CONVERTER
VIN
DC-TO-DC
OUTPUT
FEEDBACK
VIN
OUTPUT
GND
GND
Figure 33. Closed-Loop Margining System Using the ADM1169
Figure 32. Open-Loop Margining System Using the ADM1169
R1
R2
R1
R2
ATTENUATION
RESISTOR, R3
ATTENUATION
RESISTOR, R3
V
OUT
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PCB
TRACE NOISE
DECOUPLING
CAPACITOR
VH/VPx/VXx
PCB
TRACE NOISE
DECOUPLING
CAPACITOR
DACx
DACx
feedback node, and the output of the dc-to-dc converter is forced
to fall to compensate for this. The dc-to-dc converter output can be
forced high by setting the DACx output voltage lower than the
feedback node voltage. The series resistor can be split in two, and
the node between them can be decoupled with a capacitor to
ground. This can help to decouple any noise picked up from the
board. Decoupling to a ground local to the dc-to-dc converter is
recommended.
The ADM1169 can be commanded to margin a supply up or
down over the SMBus by updating the values on the relevant
DAC output.
CLOSED-LOOP SUPPLY MARGINING
A more accurate and comprehensive method of margining is to
implement a closed-loop system (see Figure 33). The voltage on
the rail to be margined can be read back to accurately margin the
rail to the target voltage. The ADM1169 incorporates all the circuits
required to do this, with the 12-bit successive approximation ADC
used to read back the level of the supervised voltages, and the
six voltage output DACs, implemented as described in the Open-
Loop Supply Margining section, used to adjust supply levels.
These circuits can be used along with other intelligence, such as
a microcontroller, to implement a closed-loop margining system
that allows any dc-to-dc converter or LDO supply to be set to
any voltage, accurate to within ±0.5% of the target.
ADM1169
MUX
ADM1169
DAC
ADC
DAC
MICROCONTROLLER
MICROCONTROLLER
CONTROLLER
(SMBus)
CONTROLLER
DEVICE
(SMBus)
DEVICE
ADM1169