PT7747C [TI]
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TEXAS INSTRUMENTS 
For assistance or to order, call (800) 531-5782
Revised 1/12/99
P T 7 7 5 0 S e r i e s
Application Notes
Mechanical Outline
Product Selector Guide
15 AMP 24V INPUT “BIG-HAMMER III”
PROGRAMMABLE ISR
The PT7750 series is a new +24V
input, 15 Amp output, high-perfor-
mance Integrated Switching Regulator
(ISR) housed in a 27-pin SIP package.
The 15A capability allows easy integra-
tion of the latest high-speed,
low-voltage µPs and bus drivers into
+24V distributed power systems.
The PT7750 series has been de-
signed to work in parallel with one or
more of the PT7747 current boosters for
increased I in increments of 15A.
out
The output voltage of the PT7750
series can be easily programmed over a
wide range with a 5-bit input. A differ-
ential remote sense is provided which
automatically compensates for any
voltage drop from the ISR to the load.
2000µF of output capacitance is
required for proper operation.
Pin-Out Information
Pin Function
Features
Pin Function
• +24V bus input
• High Efficiency
• Differential Remote
Sense
• 27-pin SIP Package
• Parallelable with
PT7747 15A current boosters
14 GND
15 GND
16 GND
17 GND
18 GND
19 GND
1
2
3
4
5
6
7
8
9
VID0
VID1
VID2
VID3
STBY* - Stand-by
VID4
Vin
Standard Application
PROGRAMMING PINS
VID0
VID1
VID2
VID3
VID4
REMOTE SENSE (+)
6
4
3
2
1
26
L1
VIN
VOUT
7
-
11
20 - 25
PT7750
1µH
27
13
-
19
5
12
20
21
22
23
24
25
26
V
V
V
V
V
V
+
+
out
out
out
out
out
out
CIN
COUT
LOAD
SYNC OUT
GND
Vin
Vin
GND
STBY*
REMOTE SENSE (-)
10 Vin
11 Vin
12 Remote Sense Gnd
13 GND
C
C
= Required 560µF electrolytic
(See input filter note)
= Required 2000µF electrolytic
in
out
L1 = Optional 1µH input choke
Remote Sense V
out
27 Sync Out
For STBY* pin:
open = output enabled
ground = output disabled.
Specifications
PT7750 SERIES
Characteristics
(Ta = 25°C unless noted)
Symbols
Conditions
Min
Typ
Max
Units
Output Current
Io
Ta = +60°C, 200 LFM
0.1*
0.1*
—
—
15**
15**
A
A
Ta = +25°C, natural convection
Input Voltage Range
Vin
0.1A ≤ Io ≤ Io max
0.1A ≤ Io ≤ Io max
Vin = +24V, Io = 15A PT7751
0°C ≤ Ta ≤ +55°C
20.0
—
—
28.0
—
V
V
Undervoltage Lockout Threshold
Output Voltage Tolerance
Vuvl
∆Vo
18.7
—
—
—
—
±80
±160
mV
mV
PT7756
Line Regulation
Load Regulation
Vo Ripple/Noise
Regline
Regload
Vn
20V ≤ Vin ≤ 28V, Io = Io max (w/remote sense)
Vin = +24V, 0.1 ≤ Io ≤ Io max (w/remote sense)
Vin = +24V, Io = Io max
—
—
—
±15
±10
75
—
—
—
mV
mV
mV
Transient Response
with Cout = 2000µF
ttr
Vos
Io step between 7.5A and 15A
Vo over/undershoot
—
—
100
200
—
—
µSec
mV
Efficiency
η
Vin = +24V, Io = 10A
Vo = 5.0V
Vo = 3.3V
Vo = 2.5V
—
—
—
88
84
80
—
—
—
%
%
%
Switching Frequency
ƒo
20V ≤ Vin ≤ 28V
0.1A ≤ Io ≤ 15A
300
0
350
—
400
+85
kHz
°C
Absolute Maximum
Operating Temperature Range
Ta
Ta
Recommended Operating
Temperature Range
Forced Air Flow = 200 LFM
At Vin = +24V, Io = 12A
0
—
+65***
°C
Storage Temperature
Weight
Ts
—
—
-40
—
—
+125
—
°C
Vertical/Horizontal
53/66
grams
* ISR-will operate down to no load with reduced specifications. Please note that this product is not short-circuit protected.
** The PT7750 series can be easily paralleled with one or more of the PT7747 Current Boosters to provide increased output current in increments of 15A.
*** See safe operating area chart.
Output Capacitors: The PT7750 series requires a minimum output capacitance of 2000µF for proper operation. Do not use Oscon type capacitors. The maximum allowable
output capacitance is (42,000 ÷ Vout)µF for the PT7751, (96,000 ÷ Vout)µF for the PT7756, or 15,000µF, whichever is less.
Input Filter: An input inductor is optional for most applications. The input inductor must be sized to handle 9ADC with a typical value of 1µH. The input capacitance
must be rated for a minimum of 8.0 Arms of ripple current when operated at maximum output current and maximum output voltage. Contact an applications engi-
neer for input capacitor selection for applications at other output voltages and output currents.
56
Power Trends, Inc. 27715 Diehl Road, Warrenville, IL 60555 (800) 531-5782 Fax: (630) 393-6902 http://www.powertrends.com
For assistance or to order, call (800) 531-5782
P T 7 7 5 0 S e r i e s
Programming Information
Ordering Information
PT7751
PT7756
PT7751❏ = 2.5 to 5.6 Volts
PT7756❏ = 6.6 to 12.8 Volts
VID4=1 VID4=0 VID4=1 VID4=0
VID3 VID2 VID1 VID0
Vout
2.5V
2.6V
2.7V
2.8V
2.9V
3.0V
3.1V
3.2V
3.3V
3.4V
3.5V
3.6V
3.7V
3.8V
3.9V
4.0V
Vout
4.1V
4.2V
4.3V
4.4V
4.5V
4.6V
4.7V
4.8V
4.9V
5.0V
5.1V
5.2V
5.3V
5.4V
5.5V
5.6V
Vout
6.6V
Vout
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
9.8V
(For dimensions and PC board layout,
see Package Styles 1000 and 1010.)
6.8V
7.0V
7.2V
7.4V
7.6V
7.8V
8.0V
8.2V
8.4V
8.6V
8.8V
9.0V
9.2V
9.4V
9.6V
10.0V
10.2V
10.4V
10.6V
10.8V
11.0V
11.2V
11.4V
11.6V
11.8V
12.0V
12.2V
12.4V
12.6V
12.8V
PT Series Suffix
(PT1234X)
Case/Pin
Configuration
Vertical Through-Hole
Horizontal Through-Hole
Horizontal Surface Mount
N
A
C
Logic 0 = Pin 12 potential (remote sense gnd)
Logic 1 = Open circuit (no pull-up resistors)
VID3 and VID4 may not be changed while the unit is operating.
C H A R A C T E R I S T I C
D A T A
Efficiency vs Output Current (@Vin=+24V)
PT7751 Safe Operating Area (@Vin=+24V, Over Vo Range)
100
90
80
70
60
50
40
Recommended
Maximum
Operating
90
80
70
60
50
40
30
20
Temperature
Vout
12.0V
5.0V
Airflow
Nat conv
60LFM
120LFM
200LFM
3.3V
2.5V
0
3
6
9
12
15
0
3
6
9
12
15
Output Current (A)
Output Current (A)
Ouput Ripple vs Output Current (@Vin=+24V)
PT7756 Safe Operating Area (@Vin=+24V, Over Vo Range)
Recommended
70
60
50
40
30
20
10
0
90
80
70
60
50
40
30
20
Maximum
Operating
Temperature
Vout
12.0V
Airflow
Nat conv
60LFM
5.0V
3.3V
2.5V
120LFM
200LFM
0
3
6
9
12
15
0
3
6
9
12
15
Output Current (A)
Output Current (A)
Power Dissipation vs Output Current (@Vin=+24V)
16
14
12
10
8
Vout
12.0V
5.0V
3.3V
2.5V
6
4
2
0
0
3
6
9
12
15
Output Current (A)
Note: SOA curves represent operating conditions at which internal components are at or below manufacturer’s maximum rated operating temperatures.
Power Trends, Inc. 27715 Diehl Road, Warrenville, IL 60555 (800) 531-5782 Fax: (630) 393-6902 http://www.powertrends.com
57
For assistance or to order, call (800) 531-5782
PT7750 Series
A p p l i c a t i o n
N o t e s
More Application Notes
Pin-Coded Output Voltage Adjustment on the
“Big Hammer III” Series ISRs
4. If active devices are used to ground the voltage control pins,
low-level open drain MOSFET devices should be used over
bipolar transistors. The inherent Vce(sat) in bipolar devices
introduces errors in the device’s internal divider network.
Discrete transistors such as the BSS138, 2N7002,
IRLML2402, or the 74C906 hex open-drain buffer are
examples of appropriate devices.
Power Trends PT7750 series ISRs incorporating pin-coded
voltage control, use pins 1, 2, 3, 4, & 6 to adjust the ouput volt-
age. The control pins are identified VID0 - VID4 respectively.
When the control pins are left open-circuit, the ISR output will
regulate at its factory trimmed output voltage. Each control pin
is internally connected to a precision resistor, and when
grounded increases the output voltage by a set amount. The
internal resistors are binary code weighted, allowing the output
voltage of the ISR to be programmed as a function of a binary
code. VID0 represents the LSB, and VID4 the MSB (or range
change bit). The output voltage ranges offered by these regula-
tors are compatible with some microprocessors, and provide a
convenient method of output voltage selection for many other
applications. Refer to Figure 1 below for the connection sche-
matic, and the PT7750 Data Sheet for the programming code
information.
Active Voltage Programming:
Special precautions should be taken when making changes to the
voltage control progam code while the unit is powered. It is
highly recommended that the ISR be either powered down or in
standby. Changes made to the program code while Vout is en-
abled induces high current transients through the device. This is
the result of the electrolytic output capacitors being either
charged or discharged to the new output voltage set-point. The
transient current can be minimized by making only incremental
changes to the binary code, i.e. one LSB at a time. A minimum
of 100µs settling time between each program state is also recom-
mended. Making non-incremental changes to VID3 and VID4
with the output enabled is discouraged. If they are changed, the
transients induced can overstress the device resulting in a perma-
nent drop in efficiency. If the use of active devices prevents the
program code being asserted prior to power-up, pull pin 5
(STBY) to the device GND during the period that the input
voltage is applied to Vin. Releasing pin 5 will then allow the
device output to execute a soft-start power-up to the pro-
grammed voltage.
Notes:
1. The programming convention is as follows:-
Logic 0:
Logic 1:
Connect to pin12 (Remote Sense Ground).
Open circuit/open drain (See notes 2, & 4)
2. Do not connect pull-up resistors to the voltage program-
ming pins.
3. To minimize output voltage error, always use pin 12 (Re-
mote Sense Ground) as the logic “0” reference. While the
regular ground (pins 13-19) can also be used for program-
ming, doing so will degrade the load reglation of the
product.
Figure 1
6
4
3
2
1
26
VID4 - VID0
SNS(+)
20-25
7-11
Vin
Vo
+24V
PT7750
1µH
(Optional)
Synch
STBY
5
GND
13-19
SNS(-)
12
Out
27
L
O
A
D
+
+
Cin
Cout
STBY
COM
3
Power Trends, Inc. 27715 Diehl Road, Warrenville, IL 60555 (800) 531-5782 Fax: (630) 393-6902 http://www.powertrends.com
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