For technical support and more information, see inside back cover or visit www.ti.com
Standard Application
Features
•18V to 36V Input Voltage Range
•Programmable Output Voltage
Range: 4.6V to 5.7V
•-40° to +85°C Ambient
•1500 VDC Isolation
•90% Efficiency
•On/Off Inhibit
•Differential Remote Sense
•40A Output with PT4494
SLTS106C
(Revised 6/21/2002)
Description
The PT4474 Excalibur™ DC/DC
converter module combines state-of-the-
art power conversion technology with
un-paralleled flexibility. Incorporating
high efficiency and ultra-fast transient
response, these modules provide up to
20A of output current over the program-
mable voltage range of 4.6V to 5.7V.
The modules include a number of
inbuilt features to facilitate system
integration. These include a foldback
output current limit, over-temperature
protection, and an inhibit on/off control.
A differential remote sense is also provided
to compensate for voltage drop between
the converter and load.
For additional output current, one
PT4474 may be operated with up to two
PT4494 compatible booster modules.
Each PT4494 adds an additional 20A of
output current capability.
•Over-Current Protection
•Over-Temperature Protection
•Over-Voltage Protection
•Space-Saving Package
•Solderable Copper Case
•Safety Approvals:
UL 60950
CSA 22.2 950
VDE EN60950 Pending
L
O
A
D
PT4474
+V
sns
+V
out
-V
out
-V
sns
7
8-13
14-19
202522 2423
VID1 - VID4
+V
in
–V
in
1
2
3
Inhibit
C
1
+
PROGRAMMING PINS
+V
OUT
+V
IN
–V
IN
–V
OUT
C
o
+
C
2
•C
o = Optional 150µF electrolytic capacitor
•C
1 = Optional 33µF, 50V electrolytic capacitor
•C
2 = Optional 1µF, 50V ceramic capacitor
• Programming pins, VID1–VID4, are shown
configured for Vo =5.0V
• For normal operation, pin 3 (Inhibit) must be
connected to –Vin.
Ordering Information
PT4474o = 4.6 to 5.7 Volts
PT4494o = 20-A Booster
PT Series Suffix (PT1234x)
Case/Pin Order Package
Configuration Suffix Code *
Vertical N(EKD)
Horizontal A(EKA)
SMD C(EKC)
* Previously known as package styles 1200,
1210, and 1215.
(Reference the applicable package code draw-
ing for the dimensions and PC board layout)
Pin-Out Information
Pin Function
1+V
in
2–V
in
3 Inhibit
4V
r †
5V
a †
6 Do not connect
7 (+)Remote Sense
8+V
out
9+V
out
10 +Vout
11 +Vout
12 +Vout
13 +Vout
Pin Function
14 –Vout
15 –Vout
16 –Vout
17 –Vout
18 –Vout
19 –Vout
20 (–)Remote Sense
21 Do not connect
22 VID1
23 VID2
24 VID3
25 VID4
26 DRV †
PT4474—24V
100-W 20- A Programmable
Isolated DC/ DC Converter
† Pins 4, 5, & 26 are used for booster applications. For
stand-alone operation, leave open circuit.
• Shaded functions indicate those pins that are
referenced to primary-side potential.
For technical support and more information, see inside back cover or visit www.ti.com
PT4470 Series Comparison
Output Voltage Configuration for
Functionality Program Range Current Sharing
PT4471 Regulator 1.3V– 3.5V N+1 with other PT4471s
PT4472 Regulator 1.3V– 3.5V With PT4495 boosters
PT4495 PT4472 Booster N/A Used only with PT4472
PT4473 Regulator 4.6V–5.7V N+1 with other PT4473s
PT4474 Regulator 4.6V–5.7V With PT4494 boosters
PT4494 PT4474 Booster N/A Used only with PT4474
PT4475 Regulator 6.5V– 17.5V N+1 with other PT4475s
PT4476 Regulator 6.5V–17.5V With PT4493 boosters
PT4493 PT4476 Booster N/A Used only with PT4476
PT4474—24V
100-W 20- A Programmable
Isolated DC/ DC Converter
Programming Information
VID4=1 VID4=0
VID3 VID2 VID1 Vout Vout
1 1 1 5.00V 4.60V
1 1 0 5.10V 4.65V
1 0 1 5.20V 4.70V
1 0 0 5.30V 4.75V
0 1 1 5.40V 4.80V
0 1 0 5.50V 4.85V
0 0 1 5.60V 4.90V
0 0 0 5.70V 4.95V
Logic 0 = Connect to (–)Remote Sense, pin 20
Logic 1 = Open circuit (no pull-up resistors)
VID4 must not be changed while the unit is operating.
Specifications (Unless otherwise stated, Ta =25°C, Vin =24V, Vo =5V, Co =0µF, and Io =Iomax)
PT4474
Characteristic Symbol Conditions Min Typ Max Units
Output Current IoOver Vin range 0 — 20 A
Input Voltage Range Vin Over Io Range 18 24 36 VDC
Set Point Voltage Tolerance Vo tol — ±1 ±1.5 %Vo
Temperature Variation Regtemp –40° ≤Tcase ≤ +100°C, Io =0 — ±0.5 — %Vo
Line Regulation Regline Over Vin range — ±0.1 ±1 %Vo
Load Regulation Regload Over Io range — ±0.5 ±1 %Vo
Total Output Voltage Variation ∆Votot Includes set-point, line, load, —±2±3%V
o
–40° ≤Tcase ≤ +100°C
Efficiency ηIo =15A — 90 — %
Vo Ripple (pk-pk) Vr20MHz bandwidth — 60 75 mVpp
Transient Response ttr 0.1A/µs load step, 50% to 75% Iomax — N/A — µs
∆Vtr Vo over/undershoot — 1 — %Vo
1A/µs load step, 50% to 100% Iomax — 75 — µs
Vo over/undershoot — ±6 — %Vo
Current Limit Ilim Vin =18V, ∆Vo = –1% —25—A
foldback continuous limit
Current Share Tolerance Ishr tol with PT4494 booster — ±10 — %
Over-Voltage Protection OVP Shutdown and latch off — 125 — %Vo
Switching Frequency ƒsOver Vin range 270 300 350 kHz
Under-Voltage Lockout UVLO — 17 — V
Inhibit (Pin 3) Referenced to –Vin (pin 2)
Input High Voltage VIH 2.5 — Open (1) V
Input Low Voltage VIL –0.5 — +0.8
Input Low Current IIL — –0.2 — mA
Standby Input Current Iin standby pins 3 & 2 connected — 4 10 mA
Internal Input Capacitance Cin —3 —µF
External Output Capacitance Cout Between +Vo and –Vo0 — 10,000 µF
Isolation Voltage Input–output/input–case 1500 — — V
Capacitance Input to output — 1100 — pF
Resistance Input to output 10 — — MΩ
Operating Temperature Range T
cCase temperature, over Vin range -40 — +115 (2) °C
Over-Temperature Shutdown OTP Case temperature, auto reset — 120 — °C
Storage Temperature Ts— -40 — +125 °C
Reliability MTBF Per Bellcore TR-332 1.4 — — 106 Hrs
50% stress, Ta =40°C, ground benign
Mechanical Shock — Per Mil-Std-883D, method 2002.3, — 500 — G’s
1mS, half-sine, mounted to a fixture
Mechanical Vibration — Mil-Std-883D, Method 2007.2 Horizontal — 20 (3) —G’s
20-2000Hz, pcb mounted
Weight — — — 90 — grams
Flammability — Materials meet UL 94V-0
Notes: (1) The Inhibit (pin 3) has an internal pull-up, which if left open circuit allows the converter to operate when input power is applied. The open-circuit is
limited to 6.5V. Refer to the application notes for interface considerations.
(2) See Safe Operating Area curves or contact the factory for the appropriate derating.
(3) The case pins on through-hole pin configuration (suffix A) must be soldered. For more information see the applicable package outline drawing.
# This specification covers only the PT4474 regulator and PT4494 current booster.
#
#
For technical support and more information, see inside back cover or visit www.ti.com
Note A: Characteristic data has been developed from actual products tested at 25°C. This data is considered typical data for the Converter.
Note B: SOA curves represent the conditions at which internal components are at or below the manufacturer’s maximum operating temperatures
Typical Characteristics
PT4474—24V
100-W 20- A Programmable
Isolated DC/ DC Converter
Stand Alone, No Heatsink
Safe Operating Area, Vin =24V (See Note B)
20
30
40
50
60
70
80
90
0 4 8 12 16 20
Iout
(
A
)
Ambient Temperature (°C)
300LFM
200LFM
100LFM
Nat conv
Airflow
Efficiency vs Output Current
Ripple vs Output Current
Power Dissipation vs Output Current
Performance Characteristics, Vo =5V (See Note A)
50
60
70
80
90
100
0 4 8 12 16 20
Iout
(
A
)
Efficiency - %
18.0V
24.0V
36.0V
VIN
0
20
40
60
80
100
0 4 8 12 16 20
Iout
(
A
)
Ripple - mV
18.0V
24.0V
36.0V
VIN
0
2
4
6
8
10
12
14
048121620
Iout
(
A
)
Pd - Watts
18.0V
24.0V
36.0V
VIN
For technical support and more information, see inside back cover or visit www.ti.com
Application Notes
Increasing the Output Current of the PT4474
with the PT4494 Compatible Current Booster
The PT4494 is a 20-A “Current Booster” module
designed specifically for the PT4474 programmable
DC/DC converter. The booster is controlled directly
by the regulator, and effectively adds an additional
output stage that operates in parallel. This allows
the system to run sychronously, providing a low
noise solution. Up to two booster modules can be
connected to a PT4474 converter. Each booster
module increases the available output current by
20A. A combination of one PT4474 converter and
two PT4494 booster modules can supply up to 60A
of output current; enough to supply a large multi-
processor system. Figure 1-1 shows the connection
schematic for the regulator and current booster
combination.
A current booster is not a stand-alone product, and
can only operate with a regulator. It is housed in
the same package as its compatible regulator, and
shares the same mechanical outline. Except for an
increase in output current, the overall performance
of a converter/booster combination is identical to
that of a stand-alone converter.
Figure 1-1; Current Booster Application Schematic
Table 1-1; Booster Pin-Out Information
Pin Function Pin Function Pin Function
1+V
in 10 +Vout 19 –Vout
2–V
in 11 +Vout 20 (–)Vsense
3 Do not connect 12 +Vout 21 Do not connect
4V
r13 +Vout 22 Do not connect
5V
a14 –Vout 23 Do not connect
6 Do not connect 15 –Vout 24 Do not connect
7 Do not connect 16 –Vout 25 Do not connect
8+V
out 17 –Vout 26 DRV
9+V
out 18 –Vout
Notes:
1. Refer to the PT4474 specification table for the
performance of the regulator/booster combination.
2. The pin-out of the current booster modules include a
number pins identified, “Do not connect” (see Table 1-1).
These pins are not connected internally to the module
but must be soldered to a pad to preserve the unit’s
mechanical integrity.
3. A minimum of 150µF of output capacitance is required
across the output of each PT4494 booster for proper
operation. A value greater than 150µF will further
reduce transients due to large and/or fast load steps.
4. The converter and all boosters must be located on
the same printed circuit board. A similar footprint
and trace layout for each module will also facilitate
current sharing.
PT4474, PT4494
PT4494
PT4474
1
2
8 - 13
–V
IN
-V
OUT
+V
OUT
20
7
REMOTE SENSE (+)
REMOTE SENSE (-)
VID1
VID2
VID3
PROGRAMMING PINS
Inhibit
3
C
IN
33µF
Optional
+
C
IN
33µF
Optional
+
LOAD
18 - 13
14 - 19
+V
IN
25
VID4
24 23 22
14-19
2
4526
204526
C
OUT
150µF
Optional
+
C
OUT
150µF
Required
3
+
Application Notes
For technical support and more information, see inside back cover or visit www.ti.com
Operating Features of the PT4470 and PT4480
Series of Isolated DC/DC Converters
Under-Voltage Lockout
An Under-Voltage Lock-Out (UVLO) inhibits the
operation of the converter until the input voltage is
above the UVLO threshold (see the applicable data
sheet specification). Below this voltage, the module’s
output is held off, irrespective of the state of the Inhibit
control (pin 3). If the Inhibit control is connected to –Vin
(pin 2), the module will automatically power up when
the input voltage rises above the UVLO threshold. The
UVLO allows the module to produce a clean transition
during both power-up and power-down, even when the
input voltage is rising or falling slowly. It also reduces
the high start-up current during normal power-up of
the converter, and minimizes the current drain from the
input source during low-input voltage conditions. The
UVLO threshold includes about 2V of hysteresis. Once
operational, the converter will conform to its operating
specifications when the minimum specified input voltage
is reached.
Over-Current Protection
To protect against load faults, the PT4470/80 series of
DC/DC converters incorporate an output current limit.
Once the load current drawn from the module reaches
the current limit threshold, any attempt by the load to
draw additional current will result in a significant drop
in the module’s regulated output voltage. The current
limit circuitry incorporates a limited amount of foldback.
This has the effect of slightly reducing the output current
from the module when supplying an absolute short circuit.
Upon removal of the load fault, the output voltage from
the converter will automatically recover to its programmed
regulation voltage.
Output Over-Voltage Protection
The PT4470/80 series of DC/DC converters incorporate
circuitry that continually senses the output for an over-
voltage (OV) condition. The OV threshold automatically
tracks the VID output voltage program setting to a level
25% higher than that programmed at the control pins,
VID0 through VID4. If the converter output voltage
exceeds the OV threshold, the converter is immediately
shut down and remains in a latched-off state. To resume
normal operation the converter must be actively reset.
This is accomplished by either cycling the status of the
Inhibit control (pin 3) from “On” to “Off” and then back
“On” again, or by momentarily removing the input power
to the converter. For failsafe operation and redundancy,
the OV protection uses circuitry that is independent of
the converter’s internal feedback loop.
Over-Temperature Protection
Over-temperature protection is provided by an internal
temperature sensor, which closely monitors the tempera-
ture of the converter’s metal case. If the case temperature
exceeds the specified limit (see applicable data sheet),
the converter will shut down. The converter will then
automatically restart when the sensed temperature drops
by about 10°C. When operated outside its recommended
thermal derating envelope (see data sheet SOA curves),
the converter will typcially cycle on and off at intervals
from a few seconds to one or two minutes. This is to ensure
that the internal components are not permanently damaged
from excessive thermal stress.
Primary-Secondary Isolation
Electrical isolation is provided between the input terminals
(primary) and the output terminals (secondary). All con-
verters are production tested to a primary-secondary
withstand voltage of 1500VDC. This specification com-
plies with UL60950 and EN60950 and the requirements
for operational isolation. Operational isolation allows
these converters to be configured for either a positive or
negative input voltage source. The data sheet ‘Pin-Out
Information’ uses shading to indicate which pins are
associated with the primary. They include pins 1 through
5, inclusive.
Fuse Recommendations
If desired, an input fuse may be added to protect against
the application of a reverse input voltage.
Thermal Considerations
Airflow may be necessary to ensure that the module can
supply the desired load current in environments with
elevated ambient temperatures. The required airflow
rate may be determined from the Safe Operating Area
(SOA) thermal derating chart (see converter specifica-
tions). The recommended direction for airflow is into
the longest side of the module’s metal case. See Figure 1.
Recommended direction for airflow is
into (perpendicular to) the longest side.
Figure 1
PT4470, PT4480 Series
For technical support and more information, see inside back cover or visit www.ti.com
Application Notes
Using the Inhibit Function on the PT4470 &
PT4480 Series of Isolated DC/DC Converters
The PT4470/44480 series of DC/DC converters incor-
porate an On/Off Inhibit function. This function may be
used in applications that demand battery conservation,
power-up/shutdown sequencing, and/or to coordinate
power-up for active in-rush current control.
The On/Off feature is provided by the Inhibit control,
pin 3. The Inhibit pin of the PT4470/4480 series of
converters is an active low enable. The pin must be
either connected, or actively pulled low, to –Vin (pin 2)
to enable the converter output (see standard applica-
tion schematic). When pins 2 & 3 are connected, the
converter provides a regulated output whenever a valid
source voltage3 is applied between +Vin (pin 1), and –Vin
(pin 2). If pin 3 is disconnected, or allowed to become
high impedance, the regulator output will be disabled. 5
Table 2-1 provides details of the interface requirements
for the Inhibit pin. Figure 2-1 shows how a discrete
MOSFET (Q1) 4, may be referenced to –Vin and used to
control the input.
Table 2-1 Inhibit Control Requirements
Parameter Min Max
Enable (VIH) –0.5V 0.8V
Disable (VIL) 2.5V (Open Circuit)
Notes:
1.
The Inhibit control uses –Vin (pin 2), on the primary side
of the converter, as its ground reference. All voltages
specified are with respect to –Vin.
2. The internal circuitry is simple pull-up resistor. The
open-circuit voltage may be as high as 6.5Vdc.
3. These converters incorporate an “Under-Voltage
Lockout” (UVLO) function. This function automatically
disables the converter output until there is sufficient input
voltage to produce a regulated output. Table 2 gives the
applicable UVLO thresholds.
Table 2-2 UVLO Thresholds 1
Series UVLO Threshold Vin Range
PT4470 17.0V Typical 18 – 36V
PT4480 34.5V Typical 36 – 75V
4.
The Inhibit input must be controlled with an open-
collector (or open-drain) discrete transistor or
MOSFET. Do not use a pull-up resistor.
5. When the converter output is disabled, the current
drawn from the input supply is typically reduced to
4mA (10mA maximum).
Figure 2-1
Turn-On Time: With input power applied, the converter
typically produces a fully regulated output voltage within
25ms after applying a low-voltage signal to the Inhibit
control pin. The actual turn-on time will vary with
the input voltage, output load, and the total amount of
capacitance connected to the output. Using the circuit of
Figure 2-1, Figure 2-2 shows the typical output voltage
and input current waveforms of a PT4472 after Q1 is
turned on. The turn on of Q1 correlates to the fall in
Vinh. The output voltage was set to 2.5V. The waveform
was measured with a 48-Vdc input voltage, and 15-A load
current.
Figure 2-2
PT4470, PT4480 Series
6. Keep the on/off transition to less than 1ms. This
prevents erratic operation of the ISR, whereby the
output voltage may drift un-regulated between 0V
and the rated output during power-up.
Vout (1V/Div)
Iin (2A/Div)
Vinh (5V/Div)
HORIZ SCALE: 5ms/Div
PT4472
+V
sns
+V
out
-V
out
-V
sns
7
8-13
14-19
2021 2522 2423
VID0 - VID4
+V
in
–V
in
1
2
3
Inhibit
C
1
+
PROGRAMMING PINS
+2.5V
+V
IN
–V
IN
0V
1 =Enable
Q
1
BSS138
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