PTB48560A_15 Datasheet, PDF (7/29 Pages) Texas Instruments – 30-W, 48-V INPUT DC/DC CONVERTERS WITH AUTO-TRACK™ SEQUENCING

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PTB48560A, PTB48560B
PTB48560C
SLTS236A – MARCH 2005 – REVISED OCTOBER 2005
TERMINAL FUNCTIONS
TERMINAL
NAME
NO.
+V_I ⁽¹⁾
1
-V_I ⁽¹⁾
4
PEN ⁽¹⁾
2
NEN ^{(1) (2)}
3
V_O Bus
10
V_O Seq
11
V_O COM
6
Track
5
–Sense
7
V_O Adjust
8
+Sense
9
DESCRIPTION
The positive input for the module with respect to -V_I. When powering the module from a negative input voltage,
this input is connected to the input source ground.
The negative input supply for the module, and the 0-V reference for the PEN and NEN enable inputs. When
powering the module from a positive source, this input is connected to the input source return.
An open-collector (open-drain) positive logic input that is referenced to -V_I. When this input is pulled to -V_I
potential the converter output is disabled. This input must be open circuit for the converter to operate. The
converter then produces an output whenever a valid input source is applied.
An open-collector (open-drain) negative logic input that is referenced to -V_I. This input must be pulled to -V_I
potential to enable the converter. When the input is open circuit, the converter output is disabled. If the enable
feature is not used, this input should be permanently connected to -V_I. The module then produces an output
whenever a valid input source is applied.
This is the positive power output with respect to V_O COM, and the main output from the converter. It is dc isolated
from the input power pins and produces a valid output voltage approximately 20 ms before the voltage at the
Track terminal is allowed to rise. This provides the required standby power source to any downstream nonisolated
modules in power-up sequencing applications.
This is a sequenced output voltage from the converter that is controlled by the Track terminal during power-up
transitions. It is only available to the PTB48560B, and used with the output voltage set to 3.3 V (an I/O supply
voltage). During power up, the voltage at V_O Seq rises with the Track terminal, typically 20 ms after the V_O Bus
output has reached regulation.
This is the output power return for both the V_O Bus and V_O Seq output voltages. This terminal should be
connected to the common of the load circuit.
This terminal is used in power-up sequencing applications to control the output voltage of Auto-Track compatible
modules, powered from the converter V_OBus output. This includes the converter V_OSeq output on the
PTB48560B. The converter Track control has an internal transistor, which holds the voltage close to V_OCOM
potential for approximately 20 ms (40 ms with the PTB48560C) after the V_OBus output is in regulation. Following
this delay, the Track voltage and V_OSeq rises simultaneously with the output voltage of all other modules
controlled by Auto-Track.
Provides the converter with a remote sense capability when used with +Sense. For optimum output voltage
accuracy, this pin should always be connected to V_OCOM, close to the load circuit. This terminal is also the
reference connection for both the output voltage set-point resistor and Track control.
A resistor must be connected between this terminal and -Sense to set the converter output voltage. A 0.05-W
rated resistor may be used, with tolerance and temperature stability of 1% and 100 ppm/°C, respectively. If left
open circuit, the converter output voltage defaults to its lowest value. The specification table gives the standard
resistor values for the most common output voltages.
The +Sense pin can be connected to V_OBus (or V_OSeq) output. When connected to V_OSeq, remote sense
compensation is delayed until the converter's power-up sequence is complete. The voltage at V_OBus is also
raised slightly. The +Sense input may be left open circuit, but connecting it to one of the output terminals improves
load regulation of that output.
(1) These functions indicate signals electrically common with the input.
(2) Denotes negative logic: Low (–V_I) = Normal operation, Open = Output off
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