®
®
A SUBSIDIARY OF C&D TECHNOLOGIES
Single Output
ULQ Models
Typical Unit
Low-Profile, Quarter-Brick
8-25 Amp Isolated DC/DC Converters
Features
■
Standard quarter-brick package/pinout
in through-hole or SMT version
Low cost; Low profile, 0.35" (8.9mm)
24V and 48V nominal inputs
Output current: 8 to 25 Amps
Output voltages: 1.2/1.5/1.8/2/2.5/3.3/5/12V
Interleaved synchronous-rectifier topology
·
Ultra high efficiency
·
No output reverse conduction
Outstanding thermal performance
On/off control, trim & sense functions
Fully isolated, 2250Vdc (BASIC)
Output overvoltage protection
Fully I/O protected; Thermal shutdown
UL/EN/IEC60950 safety approvals
Qual/HALT/EMI tested
■
■
■
■
■
■
■
■
■
■
■
■
For applications requiring improved electrical and thermal perfomance at
reduced cost DATEL's new ULQ Series "Quarter-Brick" DC/DC Converters suit
perfectly. They measure just 1.45 x 2.30 x 0.35 inches (36.8 x 58.4 x 8.9mm) and fit
the industry-standard footprint. You can also "pick-and-place" the ULQ-SMT version
optimizing your automated SMT process.
From an 18-36V or 36-75V input, ULQ's deliver outputs of 1.2, 1.5, 1.8, or 2V
fully rated at 15 or 25A, 2.5 or 3.3V at 15 or 20A, 5V at 15A and 12V at 8-10A. They
employ an interleaved, synchronous-rectifier topology that exploits 100% of their duty
cycle. They simultaneously achieve ultra-high efficiency (to 91%), tight line/load regu-
lation (±0.125/0.25%), low noise (25-70mVp-p), and quick step response (200µsec).
A state of the art, single-board, open-frame design with reduced component
count, high efficiency, low-on-resistance FET's, and planar magnetics embedded in
heavy-copper pc boards all contribute to impressive thermal derating.
The ULQ's feature set includes high isolation (2250Vdc), input pi filters, input
undervoltage shutdown, output overvoltage protection, current limiting, short-circuit
protection and thermal shutdown. The standard footprint carries on/off control (posi-
tive or negative polarity), output trim (+10/–20%) and output sense functions.
All ULQ quarter-bricks are designed to meet the BASIC-insulation requirements
of UL/EN/IEC60950 and they will carry the CE mark. Safety certifications, EMC
compliance testing and qualification testing (including HALT) are currently in prog-
ress. Contact DATEL for latest updates.
+SENSE
(7)
+V
IN
(3)
+V
OUT
(8)
SWITCH
CONTROL
–V
OUT
(4)
–V
IN
(1)
–SENSE
(5)
PWM
CONTROLLER
OPTO
ISOLATION
REFERENCE &
ERROR AMP
V
OUT
TRIM
(6)
REMOTE
ON/OFF
CONTROL*
(2)
INPUT UNDERVOLTAGE, INPUT
OVERVOLTAGE, AND OUTPUT
OVERVOLTAGE COMPARATORS
* Can be ordered with positive (standard) or negative (optional) polarity.
Figure 1. Simplified Schematic
DATEL, Inc., Mansfield, MA 02048 (USA) · Tel: (508)339-3000, (800)233-2765 Fax: (508)339-6356 · Email: sales@datel.com · Internet: www.datel.com
ULQ Series
Performance Specifications and Ordering Guide
Output
Model
➄
ULQ-1.2/25-D24
➅
ULQ-1.2/25-D48
➅
ULQ-1.5/15-D48
ULQ-1.5/25-D24
ULQ-1.5/25-D48
ULQ-1.8/15-D48
ULQ-1.8/25-D24
ULQ-1.8/25-D48
ULQ-2/15-D48
ULQ-2/25-D24
ULQ-2/25-D48
ULQ-2.5/15-D48
ULQ-2.5/20-D24
ULQ-2.5/20-D48
ULQ-3.3/15-D48
ULQ-3.3/20-D24
ULQ-3.3/20-D48
ULQ-5/15-D24
➅
ULQ-5/15-D48
➅
ULQ-12/8-D24
➅
ULQ-12/10-D48
➅
8 - 2 5 A M P, S I N G L E O U T P U T D C / D C C O N V E R T E R S
➀
Input
Regulation (Max.)
Line
±0.125%
±0.125%
±0.125%
±0.125%
±0.125%
±0.125%
±0.125%
±0.25%
±0.125%
±0.125%
±0.25%
±0.125%
±0.125%
±0.125%
±0.125%
±0.125%
±0.125%
±0.25%
±0.25%
±0.25%
±0.25%
V
OUT
(Volts)
1.2
1.2
1.5
1.5
1.5
1.8
1.8
1.8
2
2
2
2.5
2.5
2.5
3.3
3.3
3.3
5
5
12
12
I
OUT
➁
(Amps)
25
25
15
25
25
15
25
25
15
25
25
15
20
20
15
20
20
15
15
8
10
R/N (mVp-p)
➁
Typ.
50
50
25
50
45
25
50
70
25
50
70
35
50
60
45
50
45
50
50
95
90
Max.
100
100
50
100
75
50
100
100
50
100
100
55
100
100
75
100
75
100
100
130
130
Load
➂
±0.25%
±0.25%
±0.25%
±0.25%
±0.25%
±0.25%
±0.25%
±0.25%
±0.25%
±0.25%
±0.25%
±0.25%
±0.25%
±0.25%
±0.25%
±0.25%
±0.25%
±0.25%
±0.25%
±0.25%
±0.25%
V
IN
Nom.
(Volts)
24
48
48
24
48
48
24
48
48
24
48
48
24
48
48
24
48
24
48
24
48
Range
(Volts)
18-36
36-75
36-75
18-36
36-75
36-75
18-36
36-75
36-75
18-36
36-75
36-75
18-36
36-75
36-75
18-36
36-75
18-36
36-75
18-36
36-75
I
IN
➃
(mA/A)
35/1.9
35/0.8
35/0.5
50/1.8
30/0.9
35/0.6
90/2.2
45/1.1
45/0.6
50/2.4
50/1.2
45/0.9
50/2.4
45/1.2
45/1.2
80/3.1
45/1.6
50/3.5
50/1.7
90/4.4
80/2.9
Efficiency
Min.
85.5%
85%
87%
85.5%
85%
87.5%
85.5%
85.5%
87%
86%
86%
88%
86.5%
86.5%
88.5%
87.5%
88%
89%
89%
89%
88%
Typ.
88%
87.5%
89%
87.5%
87%
89%
87.5%
87.5%
89%
88%
88%
89.5%
88.5%
88.5%
90.5%
89.5%
90%
91%
91%
90.5%
90%
Package
(Case,
Pinout)
➆
C37/C40, P32
C37/C40, P32
C37/C40, P32
C37/C40, P32
C37/C40, P32
C37/C40, P32
C37/C40, P32
C37/C40, P32
C37/C40, P32
C37/C40, P32
C37/C40, P32
C37/C40, P32
C37/C40, P32
C37/C40, P32
C37/C40, P32
C37/C40, P32
C37/C40, P32
C37/C40, P32
C37/C40, P32
C37/C40, P32
C37/C40, P32
➀
Typical at T
A
= +25°C under nominal line voltage and full-load conditions. All models are
specified with an external 1µF multi-layer ceramic and 10µF capacitors across their output pins.
➁
Ripple/Noise (R/N) measured over a 20MHz bandwidth.
➂
Devices have no minimum-load requirements and will regulate under no-load conditions.
Regulation specifications describe the output voltage deviation as the line voltage or load is
varied from its nominal/midpoint value to either extreme. (Load step = 50%.)
➃
Nominal line voltage, no load/full load condition.
➄
Add "N" or "P" to the part number for Remote Control Polarity. See Part Number Structure.
➅
Contact DATEL for availability.
➆
The surface-mount package (Case C40) is not yet available on all models. Consult DATEL.
PA R T N U M B E R S T R U C T U R E
U LQ
-
3.3
/
20
-
D48 N M Lx
Output
Configuration
Quarter-Brick Package
Nominal Output Voltage
Maximum Rated Output
Pin Length Option
Surface-Mount Package
Remote On/Off Control Polarity
Input Voltage Range
See page 16 for complete Part Number Structure.
M E C H A N I C A L S P E C I F I C AT I O N S
½½½½½
½½½½½½
2.30 (58.42)
A
½½½½½½½½½½½½
½
½½½½½
½½½½½½
½½½½½
½½½½½½
½½½½½½½½½½½½½½½½½
½½½½½½½½½½½½½½½½½½½½½½½½½
½½½½½½½½½½½½½½½½½½½½
B
½½½½½½½½½½½½
½
½
½
½
2
3
Case C40
5
6
7
8
0.110
(2.79)
½
½
½
Case C37
½
½
½
½½½½½½½½½½½½
½
½
0.600
(15.24)
0.300
(7.62)
BOTTOM VIEW
½½½½½½
½½½½½½½
0.600 (15.24)
4 EQ. SP. @ 0.150 (3.81)
I/O Connections
½½½½½
½½½½½½
½½½½½½½½½½½
ALL DIMENSIONS ARE IN INCHES (MM)
COMPONENTS WILL VARY BETWEEN MODELS
½½½½½½½½½½½½½
½½½½½½½½½½
½½½½½½½½½½½½½½
Pin Function P32
1
–Input
2 Remote On/Off*
3
+Input
4
–Output
Pin
5
6
7
8
Function P32
–Sense
Output Trim
+Sense
+Output
OVERALL DIMENSIONS :
2.30 (58.42) x 1.45 (36.83) x 0.70 (17.78)
BEFORE REMOVAL OF PROTECTIVE
HEAT SHIELD
* The Remote On/Off can be provided with either
positive ("P" suffix) or negative ("N" suffix) polarity.
2
1.45 (36.83)
1
4
B
½½½½½½½½½½½½½½
½½ ½½½½½½½½½½½½½
½ ½½½½½½½½½½½½½½
½½½½½½½½½½½
½½½½½½½½½½½½½½½½
½ ½½½½½½½½½½½½½½
B
0.35
(8.89)
PROTECTIVE
HEAT SHIELD
0.125
(3.18)
8 - 2 5 A M P, S I N G L E O U T P U T C O N V E R T E R S
ULQ Models
Dynamic Characteristics
Performance/Functional Specifications
Typical @ T
A
= +25°C under nominal line voltage, full-load conditions, unless noted.
(1)
Input
Input Voltage Range:
(2)
D24 Models
D48 Models
Overvoltage Shutdown
D24 Models
D48 Models
Start-Up Threshold:
(4)
D24 Models
D48 Models
Undervoltage Shutdown:
(4)
D24 Models
D48 Models
Input Current:
Normal Operating Conditions
Inrush Transient
Short Circuit
Standby Mode:
Off, UV, Thermal Shutdown
Input Reflected Ripple Current
(5)
Internal Input Filter Type
Reverse-Polarity Protection
(3)
Dynamic Load Response
(50% Load Step)
(11)
60-300µsec, model dependent
30msec typical, 50msec maximum
160-300kHz , model dependent
4700µF
18-36 Volts (24V nominal)
36-75 Volts (48V nominal)
37-41 Volts (39V typical)
None
(3)
16-18 Volts (17.5V typical)
34-36 Volts (35V typical)
15.5-17.5 Volts (16.75V typical)
32.5-34.5 Volts (33.5V typical)
See Ordering Guide
0.05A
2
sec maximum
50-100mA
4-10mA
8-50mAp-p
Pi (0.01µF - 2.2µH - 3.3µF)
1 minute duration, 5A maximum
(1)
Start-Up Time:
(4) (12)
V
IN
to V
OUT
; On/Off to V
OUT
Switching Frequency
Maximum Capacitive Load
Calculated MTBF:
(13)
ENVIRONMENTAL
TBD million hours
(4) (14)
Operating Temperature
(Ambient):
Without Derating
With Derating
PCB Temperature:
(4) (14)
Maximum Allowable
Thermal Shutdown
Dimensions
Pin Material
Weight:
EMI
Conducted and Radiated
Safety
Model and air flow dependent
To +100°C (pcb)
+100°C
+105-120°C, +115°C typical
Physical
See Mechanical Dimensions
Copper, solder coated over nickel underplate
1 ounce (28 grams)
FCC Part 15, EN55022 may require
external filter
UL/IEC/EN60950 CSA-C22.2 No. 234
Primary-to-Secondary Insulation Level
Basic
Remote On/Off Control
(Pin 2):
(6)
Positive Logic ("P" Suffix Models)
On = open, open collector or
3.5-13V applied. I
IN
= 150µA max.
Off = pulled low to 0-0.8V I
IN
= 2mA max.
Negative Logic ("N" Suffix Models)
On = pulled low to 0-0.8V I
IN
= 2mA max.
Off = open, open collector or
3.5-13V applied. I
IN
= 150µA max.
Output
No load
20,000µF
(2)
(3)
(4)
(5)
Minimum Loading
Maximum Capacitive Loading
(7)
V
OUT
Accuracy
(Full Load):
Initial
Temperature Coefficient
Extreme
(8)
V
OUT
Trim Range
(9)
(6)
(7)
±1.25% maximum
±0.02% per °C
±3%
+10%, –20%
+10%
See Ordering Guide
See Ordering Guide
See Ordering Guide
2000Vdc minimum, D24 models
2250Vdc minimum, D48 models
100MΩ
470pF
10 Amps, typical
13 Amps, typical
17-24 Amps (20A typical)
21-29 Amps (25A typical)
26.5-36 Amps (31A typical)
Hiccup
Continuous
Comparator feedback
1.8 Volts
2.2 Volts
2.4 Volts
3 Volts
4 Volts
6.2 Volts
14.5 Volts
(8)
(9)
(10)
Remote Sense Compensation
(4)
Ripple/Noise
(20MHz BW)
Line/Load Regulation
Efficiency
Isolation Voltage:
Input-to-Output
Isolation Resistance
Isolation Capacitance
Current Limit Inception
(98% V
OUT
)
(10)
8A Models
10A Models
15A Models
20A Models
25A Models
Short Circuit:
(4)
Current
Duration
Overvoltage Protection:
(4)
1.5V
OUT
1.8V
OUT
2V
OUT
2.5V
OUT
3.3V
OUT
5V
OUT
12V
OUT
(11)
(12)
(13)
(14)
All models are tested and specified with external output capacitors (1µF ceramic in parallel
with 10µF tantalum), unless otherwise noted. These converters have no minimum-load require-½
ments and will effectively regulate under no-load conditions.
Contact DATEL for input voltage ranges other than those listed.
See Absolute Maximum Ratings for allowable input voltages.
See Technical Notes/Performance Curves for additional explanations and details.
Input Ripple Current is tested/specified over a 5-20MHz bandwidth with an external 33µF input
capacitor and a simulated source impedance of 220µF and 12µH. See I/O Filtering, Input
Ripple Current and Output Noise for details.
The On/Off Control is designed to be driven with open-collector (or equivalent) logic or the
application of appropriate voltages (referenced to –Input (pin 1)). See Remote On/Off Control
for more details.
ULQ Series DC/DC converters are unconditionally stable, including start-up and short-circuit-
shutdown situations, with capacitive loads up to 20,000µF.
Extreme Accuracy refers to the accuracy of either trimmed or untrimmed output voltages over
all normal operating ranges and combinations of input voltage, output load and temperature.
See Output Trimming for detailed trim equations.
The Current-Limit Inception point is the output current level at which the ULQ’s power-limiting
circuitry drops the output voltage 2% from its initial value. See Output Current Limiting and
Short-Circuit Protection for more details.
See Performance Curves for additional information.
For the Start-Up Time specifications, output settling is defined by the output voltage having
reached ±1% of its final value.
MTBF’s are calculated using Telcordia (Bellcore) Method 1 Case 3, ground fixed conditions,
+40°C case temperature, and full-load conditions. Contact DATEL for demonstrated life-test data.
All models are fully operational and meet published specifications, including "cold start," at –40°C.
Absolute Maximum Ratings
Input Voltage:
Continuous:
Transient (100msec):
Input Reverse-Polarity Protection
Output Current
On/Off Control (Pin 2) Max. Voltages
Referenced to –Input (pin 1)
Storage Temperature
Lead Temperature
Through-hole Soldering
SMT Soldering
D24V Models
See OVP
NA
D48V Models
81 Volts
100 Volts
Input Current must be <5A. 1 minute
duration. Fusing recommended.
Current limited. Devices can withstand
an indefinite output short circuit.
–0.3 to +13.6 Volts
–55 to +125°C
+300°C, 10 seconds
Refer to solder profile
These are stress ratings. Exposure of devices to any of these conditions may adversely
affect long-term reliability. Proper operation under conditions other than those listed in the
Performance/Functional Specifications Table is not implied, nor recommended.
3
ULQ Series
8 - 2 5 A M P, S I N G L E O U T P U T D C / D C C O N V E R T E R S
TECHNICAL NOTES
A built-in hysterisis for all models will not allow the converter to restart until
the input voltage is sufficiently reduced.
All 48V
IN
models have the overvoltage shutdown function disabled, based
on requirements to withstand brief input surges and transients to 100V for
up to 100msec without voltage interruption. Contact DATEL to have input
overvoltage shutdown for 48V
IN
models enabled.
Input Source Impedance
The input of ULQ converters must be driven from a low ac-impedance
source. The DC/DC's performance and stability can be compromised by
the use of highly inductive source impedances. The input circuit shown in
Figure 2 is a practical solution that can be used to minimize the effects of
inductance in the input traces. For optimum performance, components should
be mounted close to the DC/DC converter.
I/O Filtering, Input Ripple Current, and Output Noise
All models in the ULQ Series are tested/specified for input reflected
ripple current and output noise using the specified external input/output
components/circuits and layout as shown in the following two figures. External
input capacitors (C
IN
in Figure 2) serve primarily as energy-storage elements,
minimizing line voltage variations caused by transient IR drops in conductors
from backplane to the DC/DC. Input caps should be selected for bulk capaci-
tance (at appropriate frequencies), low ESR, and high rms-ripple-current
ratings. The switching nature of DC/DC converters requires that dc voltage
sources have low ac impedance as highly inductive source impedance can
affect system stability. In Figure 2, C
BUS
and L
BUS
simulate a typical dc
voltage bus. Your specific system configuration may necessitate additional
considerations.
TO
OSCILLOSCOPE
CURRENT
PROBE
L
BUS
C
BUS
–
1
C
IN
= 33µF, ESR < 700mΩ @ 100kHz
C
BUS
= 220µF, ESR < 100mΩ @ 100kHz
L
BUS
= 12µH
–INPUT
C
IN
Input Fusing
Certain applications and/or safety agencies may require the installation of
fuses at the inputs of power conversion components. Fuses should also be
used if the possibility of sustained, non-current-limited, input-voltage polarity
reversals exists. For DATEL ULQ series DC/DC converters, we recommend
the use of a time delay fuse, installed in the ungrounded input supply line,
with a value no greater than 20 Amps.
As a rule of thumb however, we recommend the use of a normal-blow or
slow-blow fuse with a typical value about twice the maximum input current,
calculated at low line with the converter's minimum efficiency.
All relevant national and international safety standards and regulations must
be observed by the installer. For system safety agency approvals, the
converters must be installed in compliance with the requirements of the end-
use safety standard, i.e. IEC/EN/UL60950.
Input Reverse-Polarity Protection
If the input voltage polarity is accidentally reversed, an internal diode will
become forward biased and likely draw excessive current from the power
source. If this source is not current limited or the circuit appropiately fused, it
could cause permanent damage to the converter.
Input Undervoltage Shutdown and Start-Up Threshold
Under normal start-up conditions, devices will not begin to regulate properly
until the ramping-up input voltage exceeds the Start-Up Threshold Voltage.
Once operating, devices will not turn off until the input voltage drops below
the Undervoltage Shutdown limit. Subsequent re-start will not occur until the
input is brought back up to the Start-Up Threshold. This built in hysteresis
prevents any unstable on/off situations from occurring at a single input
voltage.
Start-Up Time
The V
IN
to V
OUT
Start-Up Time is the time interval between the point at which
the ramping input voltage crosses the Start-Up Threshold and the fully loaded
output voltage enters and remains within its specified accuracy band. Actual
measured times will vary with input source impedance, external input capaci-
tance, and the slew rate and final value of the input voltage as it appears at
the converter. The ULQ Series implements a soft start circuit to limit the duty
cycle of its PWM controller at power up, thereby limiting the input inrush current.
The On/Off Control to V
OUT
start-up time assumes the converter has its
nominal input voltage applied but is turned off via the On/Off Control pin. The
specification defines the interval between the point at which the converter is
turned on (released) and the fully loaded output voltage enters and remains
within its specified accuracy band.
Similar to the V
IN
to V
OUT
start-up, the On/Off Control to V
OUT
start-up
time is also governed by the internal soft start circuitry and external load
capacitance. The difference in start up time from V
IN
to V
OUT
and from On/Off
Control to V
OUT
is therefore insignificant.
Input Overvoltage Shutdown
All 24V
IN
ULQ DC/DC's are equipped with input overvoltage protection. Input
voltages exceeding the input overvoltage shutdown specification listed in the
Performance/Functional Specifications will cause the device to shutdown.
3
+INPUT
+
V
IN
Figure 2. Measuring Input Ripple Current
In critical applications, output ripple/noise (also referred to as periodic and
random deviations or PARD) may be reduced below specified limits using fil-
tering techniques, the simplest of which is the installation of additional exter-
nal output capacitors. They function as true filter elements and should be
selected for bulk capacitance, low ESR and appropriate frequency response.
All external capacitors should have appropriate voltage ratings and be
located as close to the converter as possible. Temperature variations for all
relevant parameters should also be taken carefully into consideration. The
most effective combination of external I/O capacitors will be a function of
line voltage and source impedance, as well as particular load and layout
conditions. Our Applications Engineers can recommend potential solutions
and discuss the possibility of our modifying a given device's internal filtering
to meet your specific requirements. Contact our Applications Engineering
Group for additional details.
4
8 - 2 5 A M P, S I N G L E O U T P U T C O N V E R T E R S
ULQ Models
tion, the output voltage will decrease proportionately with increases in output
current, thereby maintaining somewhat constant power dissipation. This is
commonly referred to as power limiting. Current limit inception is defined
as the point at which the full-power output voltage falls below the specified
tolerance. See Performance/Functional Specifications. If the load current,
being drawn from the converter, is significant enough, the unit will go into a
short circuit condition as described below.
Short Circuit Condition
In Figure 3, the two copper strips simulate real-world pcb impedances
between the power supply and its load. In order to minimize measurement
errors, scope measurements should be made using BNC connectors, or the
probe ground should be less than ½ inch and soldered directly to the fixture.
+SENSE
+OUTPUT
7
8
COPPER STRIP
C1
4
5
C2
SCOPE
R
LOAD
–OUTPUT
–SENSE
COPPER STRIP
C1 = 0.1µF CERAMIC
C2 = 10µF TANTALUM
LOAD 2-3 INCHES (51-76mm) FROM MODULE
When a converter is in current-limit mode, the output voltage will drop as
the output current demand increases. If the output voltage drops too low, the
magnetically coupled voltage used to develop primary side voltages will also
drop, thereby shutting down the PWM controller. Following a time-out period,
the PWM will restart causing the output voltage to begin ramping to their
appropriate value. If the short-circuit condition persists, another shutdown
cycle will be initiated. This on/off cycling is referred to as "hiccup" mode.
The hiccup cycling reduces the average output current, thereby preventing
internal temperatures from rising to excessive levels. The ULQ Series is
capable of enduring an indefinite short circuit output condition.
Figure 3. Measuring Output Ripple/Noise (PARD)
F E AT U R E S A N D O P T I O N S
Floating Outputs
Since these are isolated DC/DC converters, their outputs are "floating" with
respect to their input. Designers will normally use the –Output (pin 4) as the
ground/return of the load circuit. You can however, use the +Output (pin 8) as
ground/return to effectively reverse the output polarity.
Minimum Output Loading Requirements
ULQ converters employ a synchronous-rectifier design topology and all
models regulate within spec and are stable under no-load to full load condi-
tions. Operation under no-load conditions however might slightly increase the
output ripple and noise.
Thermal Shutdown
The ULQ converters are equipped with thermal-shutdown circuitry. If envi-
ronmental conditions cause the temperature of the DC/DC converter to
rise above the designed operating temperature, a precision temperature
sensor will power down the unit. When the internal temperature decreases
below the threshold of the temperature sensor, the unit will self start. See
Performance/Functional Specifications.
Output Overvoltage Protection
The ULQ output voltage is monitored for an overvoltage condition using a
comparator. The signal is optically coupled to the primary side and if the
output voltage rises to a level which could be damaging to the load, the sens-
ing circuitry will power down the PWM controller causing the output voltage
to decrease. Following a time-out period the PWM will restart, causing the
output voltage to ramp to its appropriate value. If the fault condition persists,
and the output voltage again climbs to excessive levels, the overvoltage
circuitry will initiate another shutdown cycle. This on/off cycling is referred to
as "hiccup" mode.
Current Limiting
As soon as the output current increases to approximately 130% of its rated
value, the DC/DC converter will go into a current-limiting mode. In this condi-
Remote Sense
Note: The Sense and V
OUT
lines are internally connected through low-value
resistors. Nevertheless, if the sense function is not used for remote regulation
the user should connect the +Sense to +V
OUT
and -Sense to –V
OUT
at the
DC/DC converter pins.
ULQ series converters employ a sense feature to provide point of use regula-
tion, thereby overcoming moderate IR drops in pcb conductors or cabling.
The remote sense lines carry very little current and therefore require minimal
cross-sectional-area conductors. The sense lines, which are capacitively
coupled to their respective output lines, are used by the feedback control-loop
to regulate the output. As such, they are not low impedance points and must
be treated with care in layouts and cabling. Sense lines on a pcb should be
run adjacent to dc signals, preferably ground. In cables and discrete wiring
applications, twisted pair or other techniques should be implemented.
ULQ series converters will compensate for drops between the output voltage
at the DC/DC and the sense voltage at the DC/DC provided that:
[V
OUT
(+) –V
OUT
(–)] – [Sense(+) –Sense (–)]
≤
10% V
OUT
1
–INPUT
+OUTPUT
Contact and PCB resistance
losses due to IR drops
8
I
OUT
Sense Current
+SENSE
2
ON/OFF
CONTROL
7
TRIM
6
5
Sense Return
I
OUT
Return
LOAD
–SENSE
3
+INPUT
–OUTPUT
4
Contact and PCB resistance
losses due to IR drops
Figure 4. Remote Sense Circuit Configuration
5
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