SMH4046 Datasheet, PDF (16/51 Pages) List of Unclassifed Manufacturers – Hot-Swap, Active DC Output Control (ADOCTM) Power Manager with I2C lnterface

APPLICATIONS INFORMATION (CONTINUED)
SMH4046
Preliminary Information
Figure 9: SMH4046EV Margining Waveforms
Tektronix TDS3054: Time/Horizontal division = 1S
Ch 1(2V/Div) = 12V output (Yellow trace)
Ch 2 (1V/Div) = 1.8V DC-DC converter output (Blue trace)
Ch 3 (1V/Div) = 2.5V DC-DC converter output (Purple trace)
Ch 4 (1V/Div) = 5.0V output (Green trace)
Figure 10 displays the SMH4046 shutting the power
supplies (Force Shutdown) during the Sequence-On
interval due to the time-out of the Sequence
Termination Timer.
COMMENTS & PRECAUTIONS
The SMH4046 is a precision integrated circuit
requiring certain attention is spent with regards to
component selection and printed circuit board layout to
ensure the greatest possible performance. Bypass all
DC-DC converter outputs with a suitable low value
capacitor to decrease the high frequency noise and
thereby improve the SMH4046’s accuracy.
Locate the VCC bypass capacitors nearby the
SMH4046 returning the low side directly to a ground
pin on the device. Do the same for the bulk capacitor
for the DC-DC converter inputs, the 3.3V and 12V
inputs; if used. Add an additional low value bypass
capacitor if the supplies are noisy.
VCC5 Noise
Noise introduced onto the supply (VCC5 pin) of the
SMH4046 by the DC/DC converters or other sources
may affect the ADC and ADOC^tm (margining)
accuracy. The result is that the ADC reading and final
ADOC^tm (margined) voltage may exhibit an error or the
actual ADOC voltage may differ noticeably from the
target value. To obtain more accurate results, an
external series 20Ω (R47 in Figure 6) resistor should
be added in series between the VCC5 pin 41 and the
supply voltage and a 10µF ceramic bypass capacitor
(C24 in Figure 6) added from VCC5 to GND to form a
low pass filter.
ADC Function – VOUT Noise
The ADC can appear to return erroneous readings
when connected to a power supply DC/DC converter
output exhibiting a low frequency noise component.
Adding additional filter capacitance to the VMX pins
15, 18 and 21 can reduce this effect by lowering the
corner frequency of the low pass filter (C25, C26 and
C27 in Figure 6). The maximum recommended value
is 150nF.
Figure 10: SMH4046EV Forced Sequence-Off
Tektronix TDS3054: Time/Horizontal division = 40mS
Ch 1(2V/Div) = 12V output (Yellow trace)
Ch 2 (1V/Div) = 1.8V DC-DC converter output (Blue trace)
Ch 3 (1V/Div) = 2.5V DC-DC converter output (Purple trace)
Ch 4 (1V/Div) = 5.0V output (Green trace)
Summit Microelectronics, Inc
2082 1.7 08/23/04
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