Product Errata
LTC3887
October 2017
LTC3887 ERRATA
The errata below describes conditions that cause an
LTC
®
3887
device to operate differently than expected or
described in the data sheet.
ERRATA SUMMARY
ERRATA
NUMBER DESCRIPTION
1
2
MFR_ADC_CONTROL Short Round Robin Loop
When V
OUT
is Set Between 3.1V and 4.1V,
IOUT_OC_WARN May Erroneously be Detected
PAGE
1
1
based on the temperature telemetry, may be incorrect. If
the temperature readback error is above the OT or below
the UT fault limits, the part may incorrectly detect a tem-
perature fault and turn off one or both of the output rails.
Root Cause:
The MFR_ADC_COMMAND when used to only monitor a
single parameter does not update the other parameters
causing stale data. The standard round robin ADC must
be run periodically to assure data is up to date.
Workarounds:
Select Round Robin Mode all the time – This is the most
common way the part will be used.
When using MFR_ADC_CONTROL always go to standard
round robin mode after using short round robin mode for
1 round robin period, nominally 100ms.
This is required
to avoid excess temperature readings and to keep the
temperature data up to date.
ERRATA #2: IOUT_OC_WARN
The device may incorrectly detect an overcurrent warning
condition when the current is within limits if V
OUT
is set
between 3.1 and 4.1 volts.
Conditions:
The following conditions, when present simultaneously,
may expose this problem:
1) V
OUT
command is set between 3.1 and 4.1 volts
2) A large voltage transient occurs on V
OUT
due to a large
load transient or the part is turned on or off or margined
high or margined low.
L,
LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
ERRATA #1: SHORT ROUND ROBIN LOOP
When using MFR_ADC_CONTROL command 0xD8 to
monitor a specific ADC parameter or group of parameters,
the user must select standard round robin mode 0x00
for at least one round robin period, nominally 100ms.
Conditions:
The following conditions may expose this problem:
1) MFR_ADC_CONTROL command 0xD8 is set to some
value other than standard round robin mode 0x00.
2) The user commands short round robin mode directly
without first returning to standard round robin mode
0x00 for at least one full ADC period.
or
1) MFR_ADC_CONTROL command 0xD8 is set to short
round robin mode 0x0D.
2) The user commands a different non-zero mode without
first returning to standard round robin mode 0x00 for
at least one full standard round robin period.
Impact:
Erroneous temperature telemetry or out of date temperature
telemetry may be reported. In addition calculations such
as current readback and overcurrent limits, which are
er3887fa
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
1
Product Errata
Impact:
If the output voltage is set between 3.1 and 4.1 volts and
the output voltage moves, the ADC may detect a large cur-
rent when no such current exists. This large current can
trigger an overcurrent warning, possibly asserting
ALERT
low. The ADC error will have no impact on LTC3887 PWM
control or over current supervisor operation.
Root Cause:
An internal ADC calculation can cause errors when V
OUT
is set between 3.1 and 4.1 volts and the output voltage
is moving.
Workarounds:
Two workarounds are possible, depending on the system
configuration and requirements. Additional workarounds
may be possible. Contact Factory Applications for additional
assistance if required.
Work Around 1:
Use the MASK_STATUS_IOUT command 0x7b and set
bit[5] for IOUT_OC_WARN so the condition does not cause
ALERT
to pull low if an over current warning is detected.
Set command 0x7B to 0x20 (assert bit[5]). The default
MASK_STATUS_IOUT command is set to 0x20.
Work Around 2:
Set the IOUT_OC_WARN_LIMIT to 20mV divided by
IOUT_CAL_GAIN. The over current warning may exceed
the over current limit in this case causing a design rule
violation in the GUI. Ignore the design rule check and allow
the large over current warn limit. This will have no impact
on over current supervisor operation.
REVISION HISTORY
REV
A
DATE
10/17
DESCRIPTION
Delete Erratas 1 & 2 to reflect current product; Add new Errata 2
PAGE NUMBER
All
2
er3887fa
LT 1017 REV A • PRINTED IN USA
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