PTB48520W Datasheet, PDF (4/18 Pages) Texas Instruments – 25-A, 48-V INPUT ISOLATED DC/DC CONVERTER WITH AUTO-TRACK™ SEQUENCING

PTB48520W
SLTS233A – NOVEMBER 2004 – REVISED APRIL 2005
ELECTRICAL CHARACTERISTICS (continued)
(Unless otherwise stated, T_A = 25°C, V_I = 48 V, V_O = 3.3 V, C_O = 0 µF, and I_O = I_Omax)
PARAMETER
TEST CONDITIONS
MIN
OVP
Output overvoltage protection Output shutdown and latch off
UVLO
Undervoltage lockout
30
ƒ_S
Switching frequency
Over V_I range
225
Internal input capacitance
External output capacitance Between both outputs and V_O COM
Isolation voltage
Input-output
0
1500
Isolation capacitance
Input-output
Isolation resistance
Input-output
10
MTBF
Reliability
Telcordia SR-332 50% stress, T_A = 40°C,
ground benign
1.2
TYP
125
34
275
3
1000
www.ti.com
MAX
36
325
5000
UNIT
%V_o
V
kHz
µF
µF
Vdc
pF
MΩ
10⁶ Hrs
TERMINAL FUNCTIONS
TERMINAL
NAME
NO.
+V_I ⁽¹⁾
1
–V_I ⁽¹⁾
3
V_O Enable ^{(1) (2)}
2
V_O Bus
9
V_O Seq
10
V_O COM
5
Track
4
V_O Adjust
7
+Sense
8
–Sense
6
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 V_O Enable input. When powering the
module from a positive source, this input is connected to the input source return.
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 output voltage. A high impedance connection disables the module output. If the output
enable feature is not used, pin 2 should be permanently connected to –V_I. The module then produces an output
whenever a valid input source is applied.
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.
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 rises with the Track pin voltage, 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 node should be
connected to the load circuit common.
The voltage at this pin directly controls the voltage V_O Seq regulated output. It is primarily used to sequence
the voltage V_O Seq with the regulated outputs from any downstream non-isolated modules that are powered
from the converter +V_O Bus output. In these applications, the Track pin is simply connected to the track control
of each of the non-isolated modules. The Track pin 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 rises simultaneously with the output voltage of all the non-isolated modules that are under
the control of Auto-Track.
A resistor must be connected between this pin 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 this pin is
left open, the converter output voltage defaults to its lowest value. The specification table gives the preferred
resistor values for the popular bus voltages.
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 is raised
slightly. The pin may be left open circuit, but connecting it to one of the output terminals improves load
regulation of that output.
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_O COM. This pin is also the reference connection for the
output voltage set-point resistor.
(1) These functions indicate signals electrically common with the input.
(2) Denotes negative logic: Low (–V_I) = Normal operation, Open = Output off
4