®
®
INNOVATION and EXCELLENCE
Single Output
OBSO
LETE
P
R
ODUCT
O
E
Contact Fa
ctory for
Re
pl
ac
em
ent
Mo
a
Repl
ace
n
t Model
p
emen
USQ 40A Models
High-Current, Quarter-Brick
40 Amp, DC/DC Converters
Features
To 40 Amperes Output Current
Low-profile, industry standard
quarter-brick package and pinout;
1.45" x 2.28" x 0.40"
24V and 48V nominal inputs
Output Voltages: 1.2/1.5/1.8/2.5/3.3V
Outstanding efficiency: 89%
Full synchronous-rectifier topology
110mVp-p noise
Fast transient response (200μsec to 1%)
Impressive ±0.05% line/load regulation
Fully isolated, 1500Vdc guaranteed
Fully I/O protected; Thermal shutdown
Remote On/Off control
Output trim and sense functions
UL1950/EN60950 approvals, HALT
tested, EMI compliant
An unrivaled combination of power, size, long-term reliability and affordable cost
defines DATEL’s new 40 Ampere output series Quarter-Bricks. By exploiting a fully
synchronous forward topology and the newest available components, the USQ 40A
model converters achieve an 89% efficiency. The extremely high efficiency enables
these units to reliably deliver up to 40 Amps of output power from a low-height
profile, industry-standard “quarter-brick” format package (1.45" x 2.28" x 0.40") with
aluminum baseplate and open-to-airflow shell. The USQ 40A models are a pin-
compatible, high-current, companion product family to DATEL’s USQ 30A and 20A
families, and the ULQ Series 10A and 15A family of quarter bricks.
Additional features include output noise of 110 millivolts, ±0.05% line/load regu-
lation maximum, and quick transient response (200μsec to ±1%). Device functionality
includes remote on/off control (positive or negative polarity), and output trim (+10%,
–20%), sense function, and nominal input ranges of 24V (18-36V) and 48V (36-75V).
In order to safeguard both the power converter and its load, USQ 40A models,
offers the most extensive I/O protection including input undervoltage lockout, and
reverse-polarity protection, as well as output overvoltage protection, current limiting,
short-circuit protection (“hiccup” technique), and thermal shutdown (and optional
input overvoltage lockout).
The USQ 40A Series are designed to meet the BASIC insulation requirements of
UL1950 and EN60950. The “D48” models carry the CE mark. Safety certifications, as
well as EMC compliance testing and qualification testing (including HALT), have been
successfully completed. Contact DATEL for the latest information.
+SENSE
(7)
+V
OUT
(8)
+V
IN
(3)
SWITCH
CONTROL
–V
OUT
(4)
–V
IN
(1)
–SENSE
(5)
PWM
CONTROLLER
OPTO
ISOLATION
REFERENCE &
ERROR AMP
V
OUT
TRIM
(6)
INPUT UNDERVOLTAGE, INPUT
OVERVOLTAGE, AND OUTPUT
OVERVOLTAGE COMPARATORS
REMOTE
ON/OFF
CONTROL*
(2)
* 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
USQ Series
➀
40A, SINGLE OUTPUT DC/DC CONVERTERS
Performance Specifications and Ordering Guide
Output
Model
USQ-1.2/40-D24
USQ-1.2/40-D48
USQ-1.5/40-D24
USQ-1.5/40-D48
USQ-1.8/40-D24
USQ-1.8/40-D48
USQ-2.5/40-D24
USQ-2.5/40-D48
USQ-3.3/35-D24
USQ-3.3/35-D48
Input
Regulation (Max.)
Line
±0.05%
±0.05%
±0.05%
±0.05%
±0.05%
±0.05%
±0.05%
±0.05%
±0.05%
V
OUT
➁
(Volts)
1.2
1.2
1.5
1.5
1.8
1.8
2.5
2.5
3.3
3.3
I
OUT
(Amps)
40
40
40
40
40
40
40
35
35
R/N (mVp-p)
➂
Typ.
90
80
110
110
100
145
145
155
155
Max.
110
110
TBD
TBD
TBD
TBD
TBD
TBD
TBD
Load
➃
±0
.05%
±0.05%
0
±0
.05%
±0.05%
0
±0
.05%
±0.05%
0 05%
±0
.05%
±0.05%
0 05%
±0
.05%
±0.05%
0
±0
.05%
±0.05%
0
±0
.05%
±0.05%
0
±0.05%
±0.05%
V
IN
Nom.
(Volts)
➄
24
4
8
48
24
4
4
8
48
24
4
24
4
48
8
24
48
Range
(Volts)
➄
18
3
18-36
8
36-75
36
-75
6
18-36
18
-36
18-
8-
36
-75
3
6-
36-75
18-36
18
-36
8
18-36
18
-36
8
36-75
36
-75
6
18-36
36-75
I
IN
➅
(Amps)
2.4/3.5
1.23/1.76
2.9/4.0
1.5/2.1
3.5/4.9
1.8/2.5
4.7/7.0
2.4/3.3
5.4/7.5
2.8/3.9
Efficiency
80%
82%
84%
84%
84%
84%
88%
88%
89%
89%
Package
(Case,
Pinout)
C33, P32
C33, P32
C33, P32
C33, P32
C33, P32
C33, P32
C33, P32
C33, P32
C33, P32
C33, P32
48
40
±0.05%
0 05%
6
Contact
100
c
TBD
for Replacement
Model
36-75
a
Factory
o
±0.05%
a
±0
.05%
n
4
8
d
36
-75
➀
Typical at T
A
= +25°C under nominal line voltage and full-load conditions, unless otherwise
noted. All models are tested and specified with external output capacitors (1μF ceramic in
parallel with 10μF tantalum).
➁
Contact DATEL for fixed output voltages (such as 2V) other than those listed.
➂
Ripple/Noise (R/N) is tested/specified over a 20MHz bandwidth. Output noise may be further
reduced with the installation of additional external output filtering. See I/O Filtering, Input
Ripple Current, and Output Noise for details.
➃
The load-regulation specs apply over the 0-100% range. All models in the USQ Series have
no minimum-load requirements and will regulate within spec under no-load conditions (with
perhaps a slight increase in ripple/noise). Additionally, all models are unconditionally stable,
including start-up and short-circuit-shutdown situations, with capacitive loads up to 25,000μF.
➄
Contact DATEL for V
IN
ranges other than those listed.
➅
For each model, the two listed dc currents are for the following conditions: full load/nominal
input voltage and full load/low line voltage (36V). The latter is usually the worst-case condition
for input current.
PA R T N U M B E R S T R U C T U R E
U
SQ
-
2.5
/
40
-
D48
N
D
Output Configuration:
U = Unipolar/Single
Quarter-Brick Package
Nominal Output Voltage:
1.2, 1.5, 1.8, 2.5 or 3.3 Volts
M E C H A N I C A L S P E C I F I C AT I O N S
Negative Trim:
Contact DATEL for "D" suffixed negative trim devices. See Technical Notes.
Remote On/Off Control Polarity:
Add "P" for positive polarity (pin 2 open = converter on)
Add "N" for negative polarity (pin 2 open = converter off)
Input Voltage Range:
D48 = 36-75 Volts (48V nominal)
Maximum Rated Output
Current in Amps
Note: Not all part number
combinations are available.
Contact DATEL.
Case C33
2.28 (57.91)
A
BAR CODE AND
SERIAL NUMBER
APPLIED TO
THIS SURFACE.
MODEL NUMBER ON
OPPOSITE SURFACE.
2.28
(57.91)
1.860
(47.24)
0.40 MAX.
(10.16)
Optional
Heat Sink
1.03
1.45
(26.16) (36.83)
STANDOFF
0.015 (0.38)
PINS 1-3, 5-7:
0.040 ±0.001 (1.016 ±0.025)
PINS 4, 8:
0.062 ±0.001 (1.575 ±0.025)
0.15 MIN (3.81)
OPEN-FRAME, CAST
ALUMINUM CASE
A
A
B
2.00 (50.80)
B
B
1.860 (47.24)
0.140 DIA. (3.56) (4 PLACES)
1.03 (26.16)
0.600
(15.24)
2
3
(4) 0.170 DIA.
#M3 THD. THRU
WITH 0.090
THREAD RELIEF
5
6
7
8
1.45 (36.83)
1
4
0.300
(7.62)
BOTTOM VIEW
DIMENSIONS ARE IN INCHES (MM)
0.600 (15.24)
4 EQ. SP. @
0.150 (3.81)
I/O Connections
Pin Function P32
1
–Input
2 Remote On/Off*
3
+Input
4
–Output
5
–Sense
6
Output Trim
7
+Sense
8
+Output
B
*
MATERIAL: BLACK ANODIZED ALUMINUM
0.10
(2.54)
* USQ SERIES HEATSINKS ARE AVAILABLE IN 3 HEIGHTS:
0.25 (6.35), 0.50 (12.70) AND 1.00 (25.4)
Heat Sink Ordering Information
Heat Sink Height
0.25 inches (6.35mm)
0.50 inches (12.70mm)
1.00 inches (25.40mm)
DATEL Part Number
HS-QB25
HS-QB50
HS-QB100
➀
DATEL conforms to industry-standard quarter-brick pinout (see Figure 15).
➁
A "baseplate only" model with a maximum height of 0.375" (9.53mm) is
available with the addition of an "H" suffix. Contact DATEL.
* The Remote On/Off
can be provided with
either positive (standard)
or negative (optional)
polarity.
All heat sinks include 4 mounting screws and a thermal pad.
If using heatsinks other than DATEL's HS-QB series, the screw length
should accomodate the 0.090 thread relief.
2
40A, SINGLE OUTPUT DC/DC CONVERTERS
USQ Models
Performance/Functional Specifications
Typical @ T
A
= +25°C under nominal line voltage and full-load conditions, unless noted.
(1)
Dynamic Characteristics
Dynamic Load Response
(11)
Start-Up Time:
(4) (12)
V
IN to
V
OUT
On/Off
to
V
OUT
Switching Frequency
Calculated MTBF:
(13)
USQ-1.2/40-D24 -D48
USQ-1.5/40-D24 -D48
USQ-1.8/40-D24 -D48
USQ-2.5/40-D24 -D48
USQ-3.3/35-D24 -D48
Operating Temperature
(Ambient):
Without Derating
With Derating
Baseplate Temperature:
Maximum Allowable
Thermal Shutdown
Dimensions
Case Material
Baseplate Material
Shielding
Pin Material
Weight:
(4) (14)
(4) (14)
Input
Input Voltage Range:
D24 Models
D48 Models
Overvoltage Shutdown
Start-Up Threshold:
(4)
D24 Models
D48 Models
Undervoltage Shutdown:
(4)
D24 Models
D48 Models
Input Current:
Normal Operating Conditions
Inrush Transient
Standby Mode:
Off, UV, Thermal Shutdown
Input Reflected Ripple Current
IInternal Input Filter Type:
D24 Models
D48 Models
Reverse-Polarity Protection
(3)
Remote On/Off Control
(Pin 2):
(6)
Positive Logic ("P" Suffix Models)
(5)
See Dynamic Load Response
under Technical Notes
5msec typical, 8msec maximum
5msec typical, 8msec maximum
(11)
Environmental
18-36 Volts (24V nominal)
36-75 Volts (48V nominal)
None
(3)
15.5-18 Volts (16.5V nominal)
28.5-36 Volts (30V typical)
14-16.5 Volts (15.3V nominal)
27-29.5 Volts (28.3V typical)
See Ordering Guide
0.05A
2
sec maximum
4mA
6mAp-p
Pi (0.01μF - 1.5μH - 3.3μF)
Pi (0.01μF - 4.7μH - 3.3μF)
1 minute duration, 5A maximum
On = open, open collector or
2.5-5V applied. I
IN
= 150μA max.
Off = pulled low to 0-0.8V I
IN
= 800μA max.
On = pulled low to 0-0.8V I
IN
= 800μA max.
Off = open, open collector or
2.5-5V applied. I
IN
= 150μA max.
>2.5 million hours
>2.5 million hours
>2.5 million hours
>2.5 million hours
>2.5 million hours
Model and air flow dependent
To +110°C (baseplate)
+110°C
+115-122°C, +118°C typical.
Physical
1.45" x 2.28" x 0.40" (36.8 x 57.9 x 10.2mm)
Cast aluminum
Aluminum
Neither the aluminum case nor baseplate
are connected to a package pin
Brass, solder coated
1.52 ounces (43 grams)
Negative Logic ("N" Suffix Models)
Primary-to-Secondary Insulation Level
Basic
(1)
Output
Minimum Loading
Maximum Capacitive Loading
(7)
V
OUT
Accuracy
(Full Load):
Initial
Temperature Coefficient
Extreme
(8)
V
OUT
Trim Range
(9)
Remote Sense Compensation
(4)
Ripple/Noise
(20MHz BW)
Line/Load Regulation
Efficiency
Isolation Voltage:
Input-to-Output
Input-to-Case
Output-to-Case
Isolation Resistance
Isolation Capacitance
Current Limit Inception
(90% V
OUT
)
(10)
Short Circuit:
(4)
Current
Duration
Overvoltage Protection:
(4)
1.2V
OUT
1.5V
OUT
1.8V
OUT
2.5V
OUT
No load
25,000μF
±1% maximum
±0.02% per °C
±3%
+10%, –20%
+10%
See Ordering Guide
See Ordering Guide
See Ordering Guide
(2)
(3)
(4)
((5)
(6)
(7)
(8)
(9)
(10)
1500Vdc minimum
1500Vdc minimum
1500Vdc minimum
100MΩ
650pF
(11)
(12)
50A typical
(13)
Hiccup
Continuous
Magnetic feedback
1.7 Volts
2.2 Volts
2.7 Volts
3.8 Volts
(14)
All models are tested and specified with external output capacitors (1μF ceramic in parallel
with 10μF tantalum) and, unless otherwise noted. These converters have no minimum-load
requirements 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 24V input models can benefit by increasing the
33μF external input capacitance to 100μF, if the application has a high source impedance.
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.
USQ Series DC/DC converters are unconditionally stable, including start-up and short-circuit-
shutdown situations, with capacitive loads up to 25,000μF.
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 USQ’s power-limiting
circuitry drops the output voltage 10% from its initial value. See Output Current Limiting and
Short-Circuit Protection for more details.
See Dynamic Load Response under Technical Notes for detailed results including switching
frequencies. DATEL has performed extensive evaluations of Dynamic Load Response. In addi
tion to the 10μF || 1μF external capacitors, specifications are also given for 220μF || 1μF
external output capacitors for quick comparison purposes.
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 SR-332 (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.
3
USQ Series
40A, SINGLE OUTPUT DC/DC CONVERTERS
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
(Soldering, 10 sec.)
24V models
39 Volts
50 Volts
48V models
81 Volts
100 Volts
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.
In critical applications, output ripple/noise (also referred to as periodic and
random deviations or PARD) can be reduced below specified limits using
filtering techniques, the simplest of which is the installation of additional
external output capacitors. Output capacitors function as true filter elements
and should be selected for bulk capacitance, low ESR, and appropriate
frequency response. In Figure 3, the two copper strips simulate real-world
pcb impedances between the power supply and its load. Scope measurements
should be made using BNC connectors or the probe ground should be less
than ½ inch and soldered directly to the fixture.
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 be taken into consideration. OS-CON
TM
organic
semiconductor capacitors (www.sanyo.com) can be especially effective for
further reduction of ripple/noise.
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.
Input Current must be <5A. 1 minute
duration. Fusing recommended.
Current limited. Devices can withstand
an indefinite output short circuit.
–0.3 to +7 Volts
–40 to +125°C
+300°C
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.
TECHNICAL NOTES
Removal of Soldered USQ's from PCB's
Should removal of the USQ from its soldered connection be needed, it is very
important to thoroughly de-solder the pins using solder wicks or de-soldering
tools. At no time should any prying or leverage be used to remove boards that
have not been properly de-soldered first.
Input Source Impedance
USQ converters must be driven from a low ac-impedance input 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. The 24V models can benefit by increasing
the 33μF external input capacitors to 100μF, if the application has a high
source impedance.
I/O Filtering, Input Ripple Current, and Output Noise
All models in the USQ Series are tested/specified for input ripple current (also
called input reflected ripple current) and output noise using the circuits and
layout shown in Figures 2 and 3.
TO
OSCILLOSCOPE
+SENSE
+OUTPUT
7
8
COPPER STRIP
C1
4
–OUTPUT
5
–SENSE
C2
SCOPE
R
LOAD
COPPER STRIP
C1 = 1μF CERAMIC
C2 = 10μF TANTALUM
LOAD 2-3 INCHES (51-76mm) FROM MODULE
Figure 3. Measuring Output Ripple/Noise (PARD)
CURRENT
PROBE
L
BUS
Input Overvoltage Shutdown
3
+INPUT
+
V
IN
–
C
BUS
C
IN
1
–INPUT
Standard USQ DC/DC converters do not feature overvoltage shutdown.
They are equipped with this function, however. Many of our customers need
their devices to withstand brief input surges to 100V without shutting down.
Consequently, we disabled the function. Please contact us if you would like it
enabled, at any voltage, for your application.
Start-Up Threshold and Undervoltage Shutdown
Under normal start-up conditions, the USQ Series will not begin to regulate
properly until the ramping input voltage exceeds the Start-Up Threshold.
Once operating, devices will turn off when the applied voltage drops below
the Undervoltage Shutdown point. Devices will remain off as long as the
undervoltage condition continues. Units will automatically re-start when the
applied voltage is brought back above the Start-Up Threshold. The hyster-
esis built into this function avoids an indeterminate on/off condition at a single
input voltage. See Performance/Functional Specifications table for actual limits.
C
IN
= 33μF, ESR < 700mΩ @ 100kHz
C
BUS
= 220μF, ESR < 100mΩ @ 100kHz
L
BUS
= 12μH
Figure 2. Measuring Input Ripple Current
External input capacitors (C
IN
in Figure 2) serve primarily as energy-storage
elements. They should be selected for bulk capacitance (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
4
40A, SINGLE OUTPUT DC/DC CONVERTERS
USQ Models
Start-Up Time
The V
IN
to V
OUT
Start-Up Time is the interval between the point at which
a ramping input voltage crosses the Start-Up Threshold voltage and the
point at which the fully loaded output voltage enters and remains within it
specified
±1%
accuracy band. Actual measured times will vary with input
source impedance, external input capacitance, and the slew rate and final
value of the input voltage as it appears to the converter.The On/Off to V
OUT
Start-Up Time assumes the converter is turned off via the Remote On/Off
Control with the nominal input voltage already applied. The specification
defines the interval between the point at which the converter is turned on
(released) and the point at which the fully loaded output voltage enters and
remains within its specified
±1%
accuracy band.
On/Off Control
The primary-side, Remote On/Off Control function (pin 2) can be specified to
operate with either positive or negative polarity. Positive-polarity devices ("P"
suffix) are enabled when pin 2 is left open or is pulled high (+2.5-5V applied
with respect to –Input, pin 1, I
IN
< 150μA typical). Positive-polarity devices are
disabled when pin 2 is pulled low (0-0.8V with respect to –Input, I
IN
< 800μA.
Negative-polarity devices are off when pin 2 is high/open and on when pin 2
is pulled low. See Figure 4.
3
+INPUT
200k
2
ON/OFF
CONTROL
200k
REF
1
–INPUT
CONTROL
+5V
EQUIVALENT CIRCUIT FOR
POSITIVE AND NEGATIVE
LOGIC MODELS
of 5 to 15 milliseconds, the PWM will restart, causing the output voltages to begin
ramping to their appropriate values. 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
USQ is capable of enduring an indefinite short circuit output condition.
Thermal Shutdown
USQ converters are equipped with thermal-shutdown circuitry. If the internal
temperature of the DC/DC converter rises above the designed operating tem-
perature (See Performance Specifications), 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.
Output Overvoltage Protection
The output voltage is monitored for an overvoltage condition via magnetic
coupling to the primary side. If the output voltage rises to a fault condition,
which could be damaging to the load circuitry (see Performance Specifica-
tions), the sensing 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 voltages again climb to excessive
levels, the overvoltage circuitry will initiate another shutdown cycle. This
on/off cycling is referred to as "hiccup" mode.
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 the source is not current limited (<5A) nor the circuit appropriately
fused, it could cause permanent damage to the converter.
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 a sustained, non-current-limited, input-voltage polar-
ity reversal exists. For DATEL USQ Series DC/DCConverters, slow-blow
fuses are recommended with values no greater than the following:
V
OUT
Range
1.2V
OUT
Models
1.5V
OUT
Models
1.8V
OUT
Models
2.5V
OUT
Models
3.3V
OUT
Models
Fuse Value -D24
3.5 Amps
5 Amps
6 Amps
8 Amps
10 Amps
Fuse Value -D48
1.5 Amps
2.5 Amps
3 Amps
4 Amps
5 Amps
Figure 4. Driving the Remote On/Off Control Pin
Dynamic control of the remote on/off function is best accomplished with
a mechanical relay or an open-collector/open-drain drive circuit (optically
isolated if appropriate). The drive circuit should be able to sink appropriate
current (see Performance Specifications) when activated and withstand
appropriate voltage when deactivated.
Current Limiting
When power demands from the output falls within the current limit inception
range for the rated output current, the DC/DC converter will go into a current
limiting mode. In this condition the output voltage will decrease propor-
tionately with increases in output current, thereby maintaining a somewhat
constant power dissipation. This is commonly referred to as power limiting.
Current limit inception is defined as the point where the full-power output
voltage falls below the specified tolerance. If the load current being drawn
from the converter is significant enough, the unit will go into a short circuit
condition. See “Short Circuit Condition.”
Short Circuit Condition
When a converter is in current limit mode the output voltages 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
See Performance Specifications for Input Current and Inrush Transient limits.
Trimming Output Voltage
USQ converters have a trim capability (pin 6) that enables users to adjust
the output voltage from +10% to –20% (refer to the trim equations and trim
graphs that follow). Adjustments to the output voltage can be accomplished
with a single fixed resistor as shown in Figures 5 and 6. A single fixed resis-
tor can increase or decrease the output voltage depending on its connection.
Resistors should be located close to the converter and have TCR's less than
100ppm/°C to minimize sensitivity to changes in temperature. If the trim
function is not used, leave the trim pin open.
5
微控制器 MCU
京公网安备 11010802033920号
Copyright © 2005-2026 EEWORLD.com.cn, Inc. All rights reserved
电子工程世界
