Datasheet

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PTB78560x
(Top View)
NEN
Track
PEN
V
O
Seq
+Sense
−Sense
V
O
Bus
+V
I
V
O
Adjust
V
O
COM
−
V
I
PTB78560A , PTB78560B
PTB78560C
SLTS249 – JUNE 2005
TERMINAL FUNCTIONS
TERMINAL
DESCRIPTION
NAME NO.
The positive input for the module with respect to -V
I
. When powering the module from a negative input voltage,
+V
I
(1)
1
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
-V
I
(1)
4
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
PEN
(1)
2 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
NEN
(1) (2)
3
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
V
O
Bus 10
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 PTB78560B, and used with the output voltage set to 3.3 V (an I/O supply
V
O
Seq 11
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
V
O
COM 6
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
O
Bus output. This includes the converter V
O
Seq output on the
PTB78560B. The converter Track control has an internal transistor, which holds the voltage close to V
O
COM
Track 5
potential for approximately 20 ms (40 ms with the PTB78560C) after the V
O
Bus output is in regulation. Following
this delay, the Track voltage and V
O
Seq 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
–Sense 7 accuracy, this pin should always be connected to V
O
COM, 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
V
O
Adjust 8
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
O
Bus (or V
O
Seq) output. When connected to V
O
Seq, remote sense
compensation is delayed until the converter's power-up sequence is complete. The voltage at V
O
Bus is also
+Sense 9
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
Terminal Locations
7
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