TEXAS INSTRUMENTS SLTS226A Technical data

Auto-Track™

Sequencing

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PTB78520W

20-A, 18–60-V Input Auto-Track
Compatible Isolated DC/DC Converter

Description

The PTB78520W is a 20-A rated,
wide-input (18-60 V) isolated DC/DC
converter that incorporates Auto-Track™
power-up sequencing. This allows these
modules to simultaneously power up with
any other downstream non-isolated, Auto­Track compliant module.

The PTB78520W module provides
two outputs, each regulated to the same
voltage. During power up, the voltage at

Bus’ rises first, allowing this output

‘V

O

to provide input power to any downstream
non-isolated module. The voltage from

Seq’ is then allowed to rise simulta-

‘V

O

neously, under the control of Auto-Track,
along with the outputs from the down­stream modules.

Whether used to facilitate power-up
sequencing, or operated as a stand-alone
module, the PTB78520W includes many
features expected of high-performance
DC/DC converter modules. The combi-

SLTS226A – JULY 2004 – REVISED OCTOBER 2005

Features

• Wide-Input Voltage Range:

18 V to 60 V

• 20 A Total Output Current

• 90% Efficiency

• Wide-Adjust Output Voltage:

1.8 V to 3.6 V

• Over-Current Protection

• Output Over-Voltage Protection

• Over-Temperature Shutdown

• Output Enable Control

nation of input-output isolation and a
wide-input voltage range, allows operation
from either +24 V or –48 V. The wide­output adjust enables the output voltage
to be set to to any voltage over the range,

1.8 V to 3.6 V, using a single external

resistor. Precise output voltage regula­tion is assured using Smart-Sense. This
is a differential remote sense that will
intelligently regulate the sequenced out­put, depending on its sequence status.
Other operational features include an
input under-voltage lockout (UVLO) and
an output enable control. Over-current,
over-voltage, and over-temperature pro­tection assures the module’s ability to
survive any load fault.

Typical applications include distributed
power architectures in both telecom and
computing environments, particularly
complex digital systems requiring power­sequencing of multiple power supply rails.

• Auto-Track Compatible

Sequenced Output

• Smart-Sense Remote Sensing

• Under-voltage Lockout

• Industry Standard Footprint

• Surface Mountable

• 1500 VDC Isolation

• Agency Approvals (Pending):

UL/cUL 60950, EN 60950

Pin-Out Information

Pin Function

1+V

IN

2VO Enable *
3–V

IN

4 Track
5VO Com
6 (–) Sense
7 Vo Adjust
8 (+) Sense
9VO Bus
10 VO Seq

Shaded functions indicate signals
electrically common with the input.

* Denotes negative logic:

Low (–V

) = Normal operation

IN

Open = Output off

Typical Application

+V

I

–V

I

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1

+V

I

2

V

Enable

O

3

–V

I

PTB78520W

+Sense

VO Adjust

V

–Sense

Track

V

Seq

O

VO Bus

COM

O

Simultaneo us Powerup

V

C2
100 µF

1

V

2

V1 =3.3 V

V2 =1.8 V

4

8

10

9

V

PTH03050W

I

4

2

Track

GNDInhibit Adjust

15

V

O

R1

5.49 k

63

7

5

R

SET

887

6

C1
100 µF

PTB78520W

20-A, 18–60-V Input Auto-Track
Compatible Isolated DC/DC Converter

Ordering Information

Output Voltage

Code Voltage

W 1.8 V to 3.6 V

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.

(PTB78520❒xx)

Package Options

Code Description Pkg Ref.

AH Horiz. T/H (ERP)
AS SMD, Standard

(PTB78520x❒❒)

(2)

Pin Descriptions

+VIN: The positive input for the module with respect to

–VIN. When powering the module from a negative input
voltage, this input is connected to the input source ground.

–V

: The negative input supply for the module, and the

IN

0-V reference for the ‘VO 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
to –Vin potential to enable the output voltage. A high-

. This input must be pulled

IN

impedance connection will disable the module output. If
the output enable feature is not used, pin 2 should be
permanently connected to –V
produce an output whenever a valid input source is applied.

. The module will then

IN

Vo Bus: Produces a positive power output with respect

COM’. This is the main output from the converter

to ‘V

O

when operated in a stand-alone configuration. It is dc­isolated 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
the Track pin voltage, typically 20 ms after the VO Bus

Seq will rise with

O

output has reached regulation.

Vo COM: This is the output power return for both the
‘V

Bus’ and ‘VO Seq’ output voltages. This node should

O

be connected to the load circuit common.

Track: The voltage at this pin directly controls the voltage
at the ‘V
to sequence the voltage at ‘V
outputs from any downstream non-isolated modules that
are powered from the converter’s ‘+VO 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 of the PTB78520W has an internal
transistor, which holds it at ‘V
approximately 20 ms after the ‘VO Bus’ output is in
regulation. Following this delay, the ‘Track’ voltage and
‘V

Seq’ will rise simultaneously with the output voltage

O

from all the non-isolated modules, that are under the con­trol 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

Bus’ or ‘VO Seq’ outputs. When connected to ‘VO Seq’,

O

remote sense compensation will be delayed until the
power-up sequence is complete. The voltage at ‘V
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 capa­bility when used in conjunction with +Sense. For optimum
output voltage accuracy this pin should
to ‘VO COM’. This pin is also the reference connec­tion for the output voltage set-point resistor.

SLTS226A – JULY 2004 – REVISED OCTOBER 2005

(1)

(ERQ)

Seq’ regulated output. It is primarily used

O

Seq’ with the regulated

O

COM’ potential for

O

always be connected

Bus’

o

For technical support and further information visit http://power.ti.com

PTB78520W

20-A, 18–60-V Input Auto-Track
Compatible Isolated DC/DC Converter

SLTS226A – JULY 2004 – REVISED OCTOBER 2005

Environmental & Absolute Maximum Ratings

Characteristics Symbols Conditions Min Typ Max Units

Input Voltage V
Track Input Voltage V
Track Input Current I
Operating Temperature Range T

IN

TRACK

(max) From external source — — 10

TRACK

A

Over-Temperature Protection OTP PCB temperature (near pin 1) — 115 — °C
Solder Reflow Temperature T
Storage Temperatur e T

REFLOW

S

Mechanical Shock Per Mil-STD-883D, Method 2002.3 T/H — 250 — Gs

Mechanical Vibration Mil-STD-883D, Method 2007.2 T/H — 15 — Gs

Weight — — 28.5 — grams
Flammability — Meets UL 94V-O

Notes: (i) When the Track input is fed from an external voltage source, the input current

(ii) During solder reflow of SMD package version, do not elevate the module PCB, pins, or internal component temperatures above a peak of 235 °C.

Specifications (Unless otherwise stated, T

Characteristic Symbol Conditions Min Typ Max Units

Output Current I

Input Voltage Range V
Set Point Voltage Tolerance VO tol — ±0.6
Temperature Variation Reg
Line Regulation Reg
Load Regulation Reg
Total Output Voltage Variation ∆V

Output Voltage Adjust Range ∆V
Efficiency η I

Vo Ripple (pk-pk) V
Transient Response t

Track Input (pin 4)
Input Current I

Open Circuit Voltage V
Track Slew Rate Capability dV
Output Enable Input (pin 2) Referenced to –VIN (pin 3)

Input High Voltage V
Input Low Voltage V

Input Low Current I
Standby Input Current IIN standby pin 2 open — 2 — mA
No-Load Input Current IIN no-load pins 2 & 3 connected, Io
Over-Current Threshold I
Output Over-Voltage Protection OVP Output shutdown and latch off — 125 — %V
Under-Voltage Lockout UVLO 15.5 17 18 V
Switching Frequency ƒ
Internal Input Capacitance C
External Output Capacitance C
Isolation Voltage Input-output & input-case 1,500 — — Vdc

Capacitance Input-output — 1,000 — pF
Resistance Input-output 10 — — MΩ

Reliability MTBF Telcordia TR-332 1.2 — — 106 Hrs

Notes: (1) See SOA curves or consult factory for appropriate derating.

(2) When load current is supplied from the V
(3) The set-point voltage tolerance is affected by the tolerance and stability of R

with 100 ppm/°C temperature stability.

(4) When controlling the Track input from an external source the slew rate of the applied signal

the voltage to completely rise to the voltage at the Vo Bus output, at no less than the minimum specified rate, may thermally overstress the converter.

(5) The ‘VO Enable’ input has an internal pull-up, and if left open the converter output will be turned off. A discrete MOSFET or bipolar transistor is

recommended to control this input. The open-circuit voltage is approximately 20% of the input voltage. If the output enable feature is not used, this pin
should be permanently connected to –V

bus Over VIN range 0 — 20

O

IO seq 0 — 10
IO tot Sum total IO bus + IO seq 0 — 20 A

IN

temp

line

load

tot Includes set-point, line, load, — ±1.5 ±3

O

ADJ

R

TR

∆V

TR

TRACK

TRACK

TRACK

IH
IL

IL

TRIP

S

IN

OUT

Surge (100 ms maximum) — — 75 V

0 — VO Bus + 0.3 V

Over VIN Range –40 — +85 °C

Surface temperature of module or pins — — 235
— –40 — +125 °C

1 msec, ½ Sine, mounted SMD — 150 —

20-2000 Hz, PCB mounted SMD — 5 —

must be limited. A 2.74-kΩ value series resistor is recommended.

=25 °C, VIN =24 V, VO =3.3 V, CO =0 µF, and IO =IOmax)

A

PTB78520W

Over IO Range 18 48 60 V

(3)

–40° ≤TA ≤ +85°C — ±0.8 — %V
Over VIN range — ±1 — mV
Over IO range — ±1 — mV

–40° ≤TA ≤ +85°C
Over Vin range 1.8 — 3.6 V

=10 A R

O

=887 Ω,VO =3.3 V — 90 —

SET

=6.98 kΩ,VO =2.5 V — 88.5 — %

R

SET

=35.7 kΩ,VO =2.0 V — 87 —

R

SET

R

=open cct. VO =1.8 V — 86.5 —

SET

20 MHz bandwidth — 20 — mV
1 A/µs load step, 50% to 100% IOmax — 75 — µs
VO over/undershoot — ±3 — %V

pin connected to VO COM — — –0.13 mA

0—V

/dt 0.1

(4)

— 1 V/ms

2 — open
–0.2 — +0.8

— –240 — µA

=0 — 85 — mA

TOT

Shutdown, followed by auto-recovery — 30 — A

Over VIN range 225 275 325 kHz

—3 —µF

Between +Vo and –V

o

0 5,000 µF

50% stress, TA =40°C, ground benign

output, the module will exhibit higher power dissipation and slightly lower operating efficiency.

O SEQ

. The stated limit is unconditionally met if R

SET

must be greater than the minimum limit. Failure to allow

. See application notes for other interface considerations.

IN

(i)

(ii)

(1)
(1) (2)

—%V

(3)

Bus V

O

(5)

has a tolerance of 1%,

SET

mA

°C

A

%V

V

O

O

O

pp

O

O

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PTB78520W

Typical Characteristics

20-A, 18–60-V Input Auto-Track
Compatible Isolated DC/DC Converter

Characteristic Data; VIN =24 V (See Note A)

Efficiency vs. Load Current (IO Bus)

100

90

80

70

Efficiency - (%)

60

50

0 4 8 12 16 20

Output Ripple vs. Load Current (IO Bus)

50

40

30

20

Ripple - (mV)

10

Io Bus - (A)

SLTS226A – JULY 2004 – REVISED OCTOBER 2005

Characteristic Data; VIN =48 V (See Note A)

Efficiency vs. Load Current (IO Bus)

100

V

OUT

3.3V

2.5V

2.0V

1.8V

V

OUT

3.3V

2.5V

2.0V

1.8V

90

80

70

Efficiency - (%)

60

50

0 4 8 121620

Output Ripple vs. Load Current (I

50

40

30

20

Ripple - (mV)

10

Io Bus - (A)

Bus)

O

V

OUT

3.3V

2.5V

2.0V

1.8V

V

OUT

3.3V

2.5V

2.0V

1.8V

0

048121620

Power Dissipation vs. Load Current (IO Bus)

12

10

8

6

4

Power Dissipation - (W)

2

0

048121620

Io Bus - (A)

Io Bus - (A)

0

048121620

Power Dissipation vs. Load Current (IO Bus)

12

10

V

OUT

3.3V

2.5V

2.0V

1.8V

8

6

4

Power Dissipation - (W)

2

0

0 5 1 0 15 20

Io Bus - (A)

Io Bus - (A)

V

OUT

3.3V

2.5V

2.0V

1.8V

Note A: All data listed in the above graphs has been developed from actual products tested at 25 °C. This data is considered typical data for the DC-DC Converter.

For technical support and further information visit http://power.ti.com

PTB78520W

Typical Characteristics

20-A, 18–60-V Input Auto-Track
Compatible Isolated DC/DC Converter

SLTS226A – JULY 2004 – REVISED OCTOBER 2005

Safe Operating Areas; VIN =24 V (See Note B) Safe Operating Areas; VIN =48 V (See Note B)

Load Current from ‘+VO Bus’ Output

90

80

70

60

50

40

Ambient Temperature (°C)

30

20

0 4 8 121620

Load Current from ‘+VO Seq’ Output

90

80

70

60

50

40

Ambient Temperature (°C)

30

20

0246810

Output Current (A)

Output Current (A)

Airflow

400LFM
200LFM
100LFM
Nat conv

Airflow

100LFM
Nat conv

Load Current from ‘VO Bus’ Output

90

80

70

60

50

40

Ambient Temperature (°C)

30

20

0 4 8 121620

Load Current from ‘VO Seq’ Output

90

80

70

60

50

40

Ambient Temperature (°C)

30

20

0246810

Output Current (A)

Output Current (A)

Airflow

400LFM
200LFM
100LFM
Nat conv

Airflow

200LFM
100LFM
Nat conv

Note B: SOA curves represent operating conditions at which internal components are at or below manufacturer’s maximum rated operating temperature.

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