PTB78520W Datasheet, PDF (2/15 Pages) Texas Instruments – 20-A, 18–60-V Input Auto-Track Compatible Isolated DC/DC Converter

PTB78520W
Not Recommended for New Designs
20-A, 18–60-V Input Auto-Track
Compatible Isolated DC/DC Converter
SLTS226A – JULY 2004 – REVISED OCTOBER 2005
Ordering Information
Output Voltage (PTB78520❒xx)
Code
Voltage
W
1.8 V to 3.6 V
Package Options (PTB78520x❒❒)
Code
AH
AS
Description
Horiz. T/H
SMD, Standard ⁽²⁾
Pkg Ref. ⁽¹⁾
(ERP)
(ERQ)
Notes: (1) Reference the applicable package reference drawing for the dimensions and PC board layout
(2) “Standard” option specifies 63/37, Sn/Pb pin solder material.
Pin Descriptions
+V_IN: The positive input for the module with respect to
–V_IN. When powering the module from a negative input
voltage, this input is connected to the input source ground.
–V_IN: The negative input supply for the module, and the
0-V reference for the ‘V_O Enable’ input. When powering
the module from a positive source, this input is connected
to the input source return.
Vo Enable*: An open-collector (open-drain) negative logic
input that is referenced to –V_IN. This input must be pulled
to –Vin potential to enable the output voltage. A high-
impedance connection will disable the module output. If
the output enable feature is not used, pin 2 should be
permanently connected to –V_IN. The module will then
produce an output whenever a valid input source is applied.
Vo Bus: Produces a positive power output with respect
to ‘V_O COM’. This is the main output from the converter
when operated in a stand-alone configuration. It is dc-
isolated from the input power pins and is the first output
to rise when the converter is either powered or enabled.
In power-up sequencing applications, this output can
provide a 3.3-V standby source to power the downstream
non-isolated modules.
Vo Seq: This is the sequenced output voltage from the
converter. This voltage can be directly controlled from
the Track pin. During power up, V_O Seq will rise with
the Track pin voltage, typically 20 ms after the V_O Bus
output has reached regulation.
Vo COM: This is the output power return for both the
‘V_O Bus’ and ‘V_O Seq’ output voltages. This node should
be connected to the load circuit common.
Track: The voltage at this pin directly controls the voltage
at the ‘V_O Seq’ regulated output. It is primarily used
to sequence the voltage at ‘V_O Seq’ with the regulated
outputs from any downstream non-isolated modules that
are powered from the converter’s ‘+V_O Bus’ output. In
these applications, the ‘Track’ pin is simply connected
to the track control of each of the non-isolated mod-
ules. The ‘Track’ pin of the PTB78520W has an internal
transistor, which holds it at ‘V_O COM’ potential for
approximately 20 ms after the ‘V_O Bus’ output is in
regulation. Following this delay, the ‘Track’ voltage and
‘V_O Seq’ will rise simultaneously with the output voltage
from all the non-isolated modules, that are under the con-
trol of Auto-Track.
Vo Adjust: A resistor must be connected between this pin
and ‘–Sense’ to set the converter’s output voltage. A
0.05-W rated resistor may be used, with tolerance and
temperature stability of 1% and 100 ppm/°C, respectively.
If this pin is left open, the converter output voltage will
default to its lowest value. The specification table gives
the preferred resistor values for the popular bus voltages.
+Sense: The ‘+Sense’ pin can be connected to either the
‘V_O Bus’ or ‘V_O Seq’ outputs. When connected to ‘V_O Seq’,
remote sense compensation will be delayed until the
power-up sequence is complete. The voltage at ‘V_o Bus’
will also be raised slightly. The pin may be left open
circuit, but connecting it to one of the output terminals
improves load regulation of that output.
–Sense: Provides the converter with a remote sense capa-
bility when used in conjunction with +Sense. For optimum
output voltage accuracy this pin should always be connected
to ‘V_O COM’. This pin is also the reference connec-
tion for the output voltage set-point resistor.
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