BM2576
3A DC/DC
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GENERAL DESCRIPTION
FEATURES
The BM2576 series are step-down switching regulators with
all required active functions. It is capable of driving 3A load
with excellent line and load regulations. These devices are
available in fixed output voltages of 3.3V, 5V, and an
adjustable output version.
The BM2576 series offers a high-efficiency replacement for
popular three-terminal linear regulators. Also it requires a
minimum number of external components. It substantially not
only reduces the area of board size but also the size of the
heat sink, and in some cases no heat sink is required.
±4% tolerance on output voltage within specified input
voltages and output load conditions is guaranteed. Also, the
oscillator frequency accuracy is within ±10%. External
shutdown is included, featuring 70µA (typical) standby current.
The output switch includes cycle-by-cycle current limiting, as
well as thermal shutdown for full protection under fault
conditions.
Guaranteed 3A output current
3.3V, 5V, and adjustable versions
Wide input voltage range, up to 40V
Internal oscillator of 52KHz fixed frequency
Wide adjustable version output voltage range, from
1.23V to 37V±4% max over line and load conditions
Low standby current, typ. 70µA, at shutdown mode
Requires only 4 external components
Thermal shutdown and current limit protection
P+ product enhancement tested
APPLICATIONS
LCD Monitors
ADD-ON Cards Switching Regulators
High Efficiency Step-Down Regulators
Car Electronic
ORDERING INFORMATION
Package Type
TO-220 TO-263
Temperature Range Output Voltage
BM2576SCN220 BM2576SCN263 -40℃ ~ +125℃ 3.3V
BM2576ZJCN220 BM2576ZJCN263 -40℃ ~ +125℃ 5.0V
BM2576CN220 BM2576CN263 -40℃ ~ +125℃ ADJ.
BM2576
3A DC/DC
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PIN CONFIGURATION
TO-220
Top View
12 3
VIN
45
VOUT
GND
FB
ENABLE
TO-263
Top View
3
2
1
VIN
4
5
VOUT
GND
FB
ENABLE
ABSOLUTE MAXIMUM RATINGS
Input Voltage (VPOWER) …….………………………………………….……. +45V
ENABLE Pin Input Voltage ….…………………………………. –0.3V ≦V≦VIN
Operating Junction Temperature Range, TJ ……………...… 0℃ to +150℃
Storage Temperature ………………………………….….…... -65℃ to +150℃
Lead Temperature (10 sec.) ……..……………………..….…………….... 260℃
POWER DISSIPATION TABLE
Package ΘJA (℃/W) Derating factor (mW/℃)
TA >= 25℃
TA <= 25℃
Power rating (mW)
TA = 70℃
Power rating (mW)
TA = 85℃
Power rating (mW)
TO-220 45 22.2 2775 1776 1443
TO-263 45 22.2 2775 1776 1443
Note:
1. ΘJA : Thermal Resistance-Junction to Ambient, DF: Derating factor, PO: Power consumption.
Junction Temperature Calculation: TJ = TA + (PD x ΘJA ), PO = DF x (TJ – TA)
The ΘJA numbers are guidelines for the thermal performance of the device/PC-board system.
All of the above assume no ambient airflow.
2. ΘJT : Thermal Resistance-Junction to Ambient, TC: case (Tab) temperature, TJ = TC + (PD x ΘJA )
RESOMMENDED OPERATING CONDITIONS
Parameter Symbol Min. Typ. Max Units
Input Voltage (VIN) VIN 40 V
Temperature Range TJ -40 125
℃
BM2576
3A DC/DC
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ELECTRICAL CHARACTERISTICS
Electrical Characteristics at IOUT = 0mA, and TJ = +25℃; unless otherwise noted
BM2576
Parameter Device Test Conditions Min. Typ. Max. Unit
BM2576S 3.234 3.300 3.366 V Output Voltage
(Note 1) BM2576ZJ Test circuit of Figure 1 4.900 5.000 5.100 V
BM2576S 6V<=VIN <=40V 3.168 3.300 3.432 V Output Voltage
(Note 1) BM2576ZJ 8V<=VIN <=40V 0.5A<=ILOAD <=3A 4.800 5.000 5.200 V
BM2576S 6V<=VIN <=40V 3.135 3.300 3.482 V
Output Voltage
(Note 1) BM2576ZJ 8V<=VIN <=40V
0.5A<=ILOAD <=3A,
-40℃<=TJ<=125℃
Test circuit of Figure 1 4.750 5.000 5.250 V
Feedback Voltage
(Note 1) BM2576 (Adj) Test circuit of Figure 2 VOUT =5V 1.217 1.230 1.243 V
Feedback Voltage
(Note 1) BM2576 (Adj) 8V<=VIN <=40V, VOUT =5V
Test circuit of Figure 2 0.5A<=ILOAD <=3A 1.193 1.230 1.267 V
Feedback Voltage
(Note 1) BM2576 (Adj) 8V<=VIN <=40V, VOUT =5V
Test circuit of Figure 2
0.5A<=ILOAD <=3A,
-40℃<=TJ<=125℃ 1.180 1.230 1.286 V
BM2576S 75
BM2576ZJ ILOAD =3A 77
%
Efficiency
BM2576(adj) ILOAD =3A, VOUT =5V 77 %
TJ=25℃ 47 52 58
Oscillator Frequency Note 2 -40℃<=TJ<=125℃ 42 52 63
kHz
Quiescent Current Note 3 5 10 mA
Standby Current ENABLE = 5V 70 200 µA
TJ=25℃ 1.4 1.8
Saturation Voltage ILOAD =3A (Note 4) -40℃<=TJ<=125℃ 2.0
V
TJ=25℃ 50 100
Feedback Bias Current VOUT =5V
(Adj. Version only) -40℃<=TJ<=125℃ 500
nA
Duty Cycle (ON) Note 5 93 98 %
TJ=25℃ 4.2 7 8.8
Current Limit Note 2,4 -40℃<=TJ<=125℃ 3.5 7.2 9.0
A
VOUT =0V 0.3 2
Output Leakage Current Note 3 VOUT =-1V 9 20 mA
TJ=25℃ 2.2 1.4
VIH (VOUT =0V) -40℃<=TJ<=125℃ 2.4 V
TJ=25℃ 1.2 1.0
ENABLE Threshold Voltage VIL (VOUT = Normal Output
Voltage) -40℃<=TJ<=125℃ 0.8
V
IIH (ENABLE = 5V) 12 30
ENABLE Input Current IIH (ENABLE = 0V) 0 10
µA
BM2576
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Note 1: External components such as the catch diode, inductor, input and output capacitors can affect switching regulator system
performance. Refer to Application Information for details.
Note 2: The oscillator frequency reduces to approximately 11KHz in the event of fault conditions, such as output short or
overload. And the regulated output voltage will drop approximately 40% from the nominal output voltage. This self-protection
feature lowers the average power dissipation by lowering the minimum duty cycle from 5% down to approximately 2%.
Note 3: For these parameters, FB is removed from VOUT and connected to +12V to force the output transistor OFF.
Note 4: VOUT pin sourcing current. No diode, inductor or capacitor connect to VOUT.
Note 5: FB is removed from VOUT and connected to 0V.
BLOCK DIAGRAM
BM2576
3A DC/DC
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APPLICATION CIRCUIT
BM2576
BM2576
BM2576
3A DC/DC
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Page 6
TYPICAL CHARACTERISTICS
BM2576
3A DC/DC
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BM2576
3A DC/DC
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APPLICATION INFORMATION
It is required that VIN must be bypassed with at least a 100uF electrolytic capacitor for stability. Also, it is strongly recommended
the capacitor’s leads must be dept short, and located near the regulator as possible.
For low operating temperature range, for example, below -25℃, the input capacitor value may need to be larger. This is due to
the reason that the capacitance value of electrolytic capacitors decreases and the ESR increases with lower temperatures and
age. Paralleling a ceramic or solid tantalum capacitor will increase the regulator stability at cold temperatures.
Output Capacitors (COUT)
An output capacitor is also required to filter the output voltage and is needed for loop stability. The capacitor should be located
near the BM2576 using short PC board traces. Low ESR types capacitors are recommended for low output ripple voltage and
good stability. Generally, low value or low voltage (less than 12V) electrolytic capacitors usually have higher ESR numbers. For
example, the lower capacitor values (220uF – 1000uF) will yield typically 50mV to 150mV of output ripple voltage, while
larger-value capacitors will reduce the ripple to approximately 20mV to 50mV.
The amount of output ripple voltage is primarily a function of the ESR (Equivalent Series Resistance) of the output capacitor and
the amplitude of the inductor ripple current (△IIND).
Output Ripple Voltage = (△IIND) x (ESR of COUT)
Some capacitors called “high-frequency”, “low-inductance”, or “low-ESR” are recommended to use to further reduce the output
ripple voltage to 10mV or 20mV. However, very low ESR capacitors, such as Tantalum capacitors, should be carefully evaluated.
Catch Diode
This diode is required to provide a return path for the inductor current when the switch is off. It should be located close to the
BM2576 using short leads and short printed circuit traces as possible.
To satisfy the need of fast switching speed and low forward voltage drop, Schottky diodes are widely used to provide the best
efficiency, especially in low output voltage switching regulators (less than 5V). Besides, fast-Recovery, high-efficiency, or
ultra-fast recovery diodes are also suitable. But some types with an abrupt turn-off characteristic may cause instability and EMI
problems. A fast-recovery diode with soft recovery characteristics is better choice.
BM2576
3A DC/DC
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Output Voltage Ripple and Transients
The output ripple voltage is due mainly to the inductor sawtooth ripple current multiplied by the ESR of the output capacitor. The
output ripple voltage of a switching power supply will contain a sawtooth ripple voltages at the switcher frequency, typically about
1% of the output voltages, and may also contain short voltage spikes of the sawtooth waveform.
Due to the fast switching action, and the parasitic inductance of the output filter capacitor, there is voltage spikes presenting at
the peaks of the sawtooth waveform. Cautions must be taken for stray capacitance, wiring inductance, and even the scope
probes used for transients evaluation. To minimize these voltage spikes, shortening the lead length and PCB traces is always the
first thought. Further more, an additional small LC filter (30uH & 100uF) (as shown in Figure 3) will possibly provide a 10X
reduction in output ripple voltage and transients.
Inductor Selection
The BM2576 can be used for either continuous or discontinuous modes of operation. Each mode has distinctively different
operating characteristics, which can affect the regulator performance and requirements.
With relatively heavy load currents, the circuit operates in the continuous mode (inductor current always flowing), but under light
load conditions, the circuit will be forced to the discontinuous mode (inductor current falls to zero for a period of time). For light
loads (less than approximately 300mA) it may be desirable to operate the regulator in the discontinuous mode, primarily because
of the lower inductor values required for the discontinuous mode.
Inductors are available in different styles such as pot core, toriod, E-frame, bobbin core, et., as well as different core materials,
such as ferrites and powdered iron. The least expensive, the bobbin core type, consists of wire wrapped on a ferrite rod core.
This type of construction makes for an inexpensive inductor, but since the magnetic flux is not completely contained within the
core, it generates more electromagnetic interference (EMI). This EMI can cause problems in sensitive circuits, or can give
incorrect scope readings because of induced voltages in the scope probe.
BM2576
3A DC/DC
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Page 10
An inductor should not be operated beyond its maximum rated current because it may saturate. When an inductor begins to
saturate, the inductance decreases rapidly and the inductor begins to look mainly resistive (the DC resistance of the winding).
This will cause the switch current to rise very rapidly. Different inductor types have different saturation characteristics, and this
should be well considered when selecting as inductor.
Feedback Connection
For fixed output voltage version, the FB (feedback) pin must be connected to VOUT. For the adjustable version, it is important to
place the output voltage ratio resistors near BM2576 as possible in order to minimize the noise introduction.
ENABLE
It is required that the ENABLE must not be left open. For normal operation, connect this pin to a “LOW” voltage (typically, below
1.6V). On the other hand, for standby mode, connect this pin with a “HIGH” voltage. This pin can be safely pulled up to +VIN
without a resistor in series with it.
Grounding
To maintain output voltage stability, the power ground connections must be low-impedance. For the 5-lead TO-220 and TO-263
style package, both the tab and pin 3 are ground and either connection may be used.
Heatsink and Thermal Consideration
Although the BM2576 requires only a small heatsink for most cases, the following thermal consideration is important for all
operation. With the package thermal resistances θJA and θJC, total power dissipation can be estimated as follows:
PD = (VIN x IQ) + (VOUT / VIN)(ILOAD x VSAT);
When no heatsink is used, the junction temperature rise can be determined by the following:
∆TJ = PD x θJA;
With the ambient temerpature, the actual junction temperature will be:
TJ = ∆TJ + TA;
If the actual operating junction temperature is out of the safe operating junction temperature (typically 125℃), then a heatsink is
required. When using a heatsink, the junction temperature rise will be reduced by the following:
∆TJ = PD x (θJC + θinterface + θHeatsink);
Also one can see from the above, it is important to choose an heatsink with adequate size and thermal resistance, such that to
maintain the regulator’s junction temperature below the maximum operating temperature.
BM2576
3A DC/DC
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PACKAGE DIMENSION
TO-220 (N220)
R
S
J
K
N
A
C
B
D
F
G
123
T
S
C
T
J
R
B
A
F
45
D
G
N
K
TO-263 (N263)
AD
C
B
I
E
L
F
G
K
