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WEITRON
2A Step-down Voltage Regulator
P b Lead(Pb)-Free
General Description: Power Converter 52kHz
WT2575M
The WT2575 series of regulators are monolithic integrated circuits that provide all the active functions for a step-down (buck) switching regulator, capable of driving 2A load with excellent line and load regulation. These devices are available in fixed output voltages of 3.3V, 5V, 12V and an ADJ output version. Requiring a minimum number of external components, these regulators are simple to use and include internal frequency compensation and a fixed-frequency oscillator. The WT2575 series offers a high-efficiency replacement for popular three-terminal linear regulators. It substantially reduces the size of the heat sink, and in some cases no heat sink is required. A standard series of inductors optimized for use with the WT2575 are available from several different manufacturers. This feature greatly simplifies the design of switch-mode power supplies. Other features include a guaranteed 4% tolerance on output voltage within specified input voltages and output load conditions, and 10% on the oscillator frequency. External shutdown is included, featuring 50 A (typical) standby current. The output switch includes cycle-by-cycle current limiting, as well as thermal shutdown for full protection under fault conditions.
Features:
* 3.3V, 5V, 12V and adjustable output versions * Adjustable version output voltage range, 1.23V to 37V 4% max over line and load conditions * Guaranteed 2A output current * Wide input voltage range up to 40V * Requires only 4 external components * 52kHz fixed frequency internal oscillator * TTLshutdown capability, low powerstandby mode * High efficiency * Uses readily available standard inductors * Thermal shutdownand current limit protection
Applications:
* Simple high-efficiency step-down (buck) regulator * Efficient pre-regulator for linear regulators * On-card switching regulators * Positive to negative converter (Buck-Boost)
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WT2575M
Ordering Information
Part Number WT2575M33 WT2575M50 WT2575M12 WT2575M Voltage 3.3V 5.0V 12.0V ADJ Package SOP-8 SOP-8 SOP-8 SOP-8
Packing Type
2,500Units / Tape & Reel 2,500Units / Tape & Reel 2,500Units / Tape & Reel 2,500Units / Tape & Reel
Connection Diagrams
Surface Mount Package (Top View)
SOP- 8
GND GND
GND GND
8765
WT YWW 2575M 50
1234
Vin Vout ON/OFF FB Y WW =Year =Weekly
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WT2575M
Typical Application
7V - 40V Unregulated DC Input +VIN Feedback
WT2575M
Output GND ON/ OFF
100H L1
+5V Regulated Output 2A Load + COUT 680F
+
CIN 100F
D1 1N5822
Low Noise APPLICATIONS
7V - 40V Unregulated DC Input +VIN 1
WT2575M
5~8 GND
Feedback 3 Output 2 ON/ OFF D1 1N5822 47H L1 + COUT 220F 0.47H L1 + COUT 220F +5V Regulated Output 2A Load
+
4
CIN 100F
+VIN --This is the positive input supply for the IC switching regulator. A suitable input bypass capacitor must be present at this pin to minimize voltage transients and to supply the switching currents needed by the regulator. Ground --Circuit ground. Output --Internal switch, the voltage at this pin switches between (+VIN VSAT) and approximately -0.5V. To minimize coupling to sensitive circuitry, the PC board copper area connected to this pin should be kept to a minimum. FeedBack --Senses the regulated output voltage to complete the feedback loop. --Allows the switching regulator circuit to be shut down using logic level signals. Pulling this pin below a threshold voltage of approximately 1.5V turns the regulator on, and pin can be wired to the ground pin or it can be left open, shutdown feature is not needed, the in either case the regulator will be in the ON condition.
Pin Functions:
Block Diagram
Unregulated DC Input
+
V IN
Internal Regulator
ON/OFF
ON/OFF
CIN
Feedback
R2 + 1.0K R1 -
Fixed Gain Error AMP
Comparator + -
3 AMP Switch Driver Output L1 D1
VOUT
+
1.23V Band-Gap Reference
52kHz Oscillator
Reset
Thermal Shutdown
Current Limit GND
C out
L O A D
3.3V R2 = 1.7K 5V, R2 = 3.1K For ADJ Version R1 = Open, R2 = 0
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WT2575M
Absolute Maximum Ratings (Note1)
Parameter Maximum Supply Voltage Pin Input voltage Output Voltage to Ground (Steady state) Power Dissipation Storage Temperature Range ESD Susceptibility (Human Body Model) Maximum Junction Temperature Rating 45 0.3+ VIN 1 Internally limited 65150 2 150 KV Unit V V V --
Operating Ratings
Temperature Range Supply Voltage 40125 640 V
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WT2575M
Electrical Characteristics Specifications with standard type face are for TJ = 25C
Symbol WT2575M VOUT Parameter Conditions Min (Note2) Typ Max (Note 2) Units
3.3 V System Parameters (Note 3) Test Circuit Figure 2 Output Voltage Efficiency 6V VIN 40V 0.5A ILOAD 2A VIN = 12V, ILOAD = 2A 8V VIN 40V 0.5A ILOAD 2A VIN = 12V, ILOAD = 2A 3.234 -3.3 73 3.366 -V %
WT2575M VOUT
5V System Parameters (Note 3) Test Circuit Figure 2 Output Voltage Efficiency 4.800 -5.0 77 5.20 -V %
WT2575M VOUT
12V
System Parameters (Note 3) Test Circuit Figure 2 15V VIN 40V 0.5A ILOAD 2A VIN = 15V, ILOAD = 2A 11.52 -12.0 88 12.48 -V %
Feedback Voltage Efficiency
WT2575M VOUT
ADJ System Parameters (Note 3) Test Circuit Figure 2 Feedback Voltage Efficiency 8V VIN 40V 0.5A ILOAD 2A VOUT = 5V VIN = 12V, ILOAD = 2A VOUT = 5V 1.193 -1.230 77 1.267 -V %
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WT2575M
All Output Voltage Versions Electrical Characteristics (Conditions TJ = 25 )
Symbol Parameter Conditions Min (Note2) Typ Max (Note 2) Units
Device Parameters Ib fO VSAT DC ICL IL IQ ISTBY Feedback Bias Current Oscillator Frequency VSAT Saturation Voltage Max Duty Cycle(ON) Current Limit Output Leakage Current Quiescent Current Standby Quiescent Current Adjustable Version Only, VOUT= 5V (Note 8 ) IOUT=2A(Note 4) (Note 5) (Notes 4, 8 ) Output = 0V (Note 6,7) Output = -1V(Note 10) (Note 6) PIN = 5V (OFF) -47 -93 4.2 ----50 52 1.4 98 5.8 7.5 5 50 100 58 1.8 -6.9 2.3 30 10 200 nA KHz V % A mA mA mA A
CONTROL VIH VIL IIH IIL VOUT = 0V Pin Logic Input Level VOUT = Nominal Output Voltage ON/OFF Pin = 5V(OFF) Pin Input Current ON/OFF Pin = 0V(ON) 2.2 ---1.4 1.2 12 0 -1.0 30 10 V V A A
Note 1 Absolute Maximum Ratings indicates limits beyond which damage to the device May occur. Operating Ratings indicate conditions for which the device is intended to be functional, but specific performance is not guaranteed. For guaranteed specifications and the best conditions, see the Electrical Characteristics. Note 2 All limits guaranteed at room temperature (standard type face) and at temperature extremes (bold type face). All room temperature limits are 100% production tested. All limits at temperature extremes are guaranteed via correlation using standard Statistical Quality Control (SQC) methods. Note 3 External components such as the catch diode, inductor, input and output capacitors, and voltage programming resistors can affect switching regulator system performance. Note 4 Output pin sourcing current. No diode, inductor or capacitor connected to output pin. Note 5 Feedback pin removed from output and connected to 0V. Note 6 Feedback pin removed from output and connected to +12V for the 3.3V, 5V, and the ADJ version,
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WT2575M
to force the output transistor switch OFF. Note 7 VIN = 40V Note 8 The oscillator frequency reduces to approximately 11 KHz in the event of an output short or an overload which causes the regulated output voltage to drop approximately 40% from the nominal output voltage. The self-protection feature lowers the average power dissipation of the minimum duty cycle from 5% down to approximately 2%.
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WT2575M
Typical Performance Characteristics
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TEST CIRCUIT AND LAYOUT GUIDELINES
Careful layout is important with any switching regulator. Rapidly switching currents associated with wiring inductance generate voltage transients which can cause problems. To minimize inductance and ground loops, the lengths of the leads indicated by heavy lines in Figure 1 below should be kept as short as possible. Singlepoint grounding (as indicated in Figure 1) or ground plane construction should be used for best results. When using the Adjustable version, place the programming resistors as close as possible to WT2575M, to keep the sensitive feedback wiring short.
Figure.1a Fixed Output Voltage Versions
Feedback +VIN
WT2575M FIXED OUTPUT
Output L1 100F D1 MBR360 + COUT 680F L O A D VOUT
VIN Unregulated DC Input
GND + CIN 100F
ON/OFF
CIN - 100F, 75V, Aluminum Electrolytic COUT - 680F, 25V, Aluminum Electrolytic D1 L1 R1 R2 Schottky, MBR360 100H, 3L Electronic Corp. TC-101M-3.0A-6826 2k, 0.1% 6.12k, 0.1%
Feedback +VIN
WT2575M-ADJ
ON/ OFF
Output
L1 100H D1 MBR360 + COUT 680F
VOUT=5.0V R2 L O A D
7V - 40V Unregulated DC Input
+
GND
CIN 100F
R1
VOUT = VREF ( 1 +
VOUT R2 = R1 ( V -1) REF
R2 ) R1
where VREF = 1.23V, R1 between 1k and 5k.
Figure.1b Adjustable Output Voltage Versions
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INPUT CAPACITOR CIN --A low ESR aluminum or tantalum bypass capacitor is needed between the input pin and ground pin. It must be located near the regulator using short leads. This capacitor prevents large voltage transients from appearing at the input, and provides the instantaneous current needed each time the switch turns on. Selecting an input capacitor requires consulting the manufacturers data sheet for maximum allowable RMS ripple current. For a maximum ambient temperature of 40C, a general guideline would be to select a capacitor with a ripple current rating of approximately 50% of the DC load current. For ambient temperatures up to 70C, a current rating of 75% of the DC load current would be a good choice for a conservative design. The capacitor voltage rating must be at least 1.25 times greater than the maximum input voltage, and often a much higher voltage capacitor is needed to satisfy the RMS current requirements. OUTPUT CAPACITOR COUT ---An output capacitor is required to filter the output and provide regulator loop stability. Low impedance or low ESR Electrolytic or solid tantalum capacitors designed for switching regulator applications must be used. When selecting an output capacitor, the important capacitor parameters are; the 100 kHz Equivalent Series resistance (ESR), the RMS ripples current rating, voltage rating, and capacitance value. For the output capacitor, the ESR value is the most important parameter. The output capacitor requires an ESR value that has an upper and lower limit. For low output ripple voltage, a low ESR value is needed. This value is determined by the maximum allow able output ripple voltage, typically 1% to 2% of the output voltage. But if the selected capacitor's ESR is extremely low, there is a possibility of an unstable feedback loop, resulting in an oscillation at the output. CATCH DIODE D ---Buck regulators require a diode to provide a return path for the inductor current when the switch turns off. This must be a fast diode and must be located close to the WT2575 using short leads and short printed circuit traces. Because of their very fast switching speed and low forward voltage drop, Schottky diodes provide the best performance, especially in low output voltage applications (5V and lower). Ultra fast recovery, or High-Efficiency rectifiers are also a good choice, but some types with an abrupt turnoff characteristic may cause instability or EMI problems. INDUCTOR SELECTION L ---All switching regulators have two basic modes of operation; continuous and discontinuous. The difference between the two types relates to the inductor current, whether it is flowing continuously, or if it drops to zero for a period of time in the normal switching cycle. Each mode has distinctively different operating characteristics, which can affect the regulators performance and requirements. Most switcher designs will operate in the discontinuous mode when the load current is low. The WT2575 (or any of the Simple Switcher family) can be used for both continuous and discontinuous modes of operation. There is a formula for general applications:
(Note The unit of voltage is V, the unit of current is A)
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WT2575M
SOP-8 PACKAGE OUTLINE DIMENSIONS(Unit: mm)
4.915 0.085 3.874 0.064 0.381 0.127
1.395 0.125 5.995 0.205
PIN INDENT
0.215 0.035 0 ~8
0.065 0.035
3.925 0.064
0.840 0.430
1.041 0.178 0.420 0.009 1.270 0.250 3.555 0.225
1.550 0.178
1.391 0.127
0.176 0.074
ORDERING NUMBER
WT2575 M XX
Circuit Type Output Voltage 33 : 3.3V 50 : 5.0V 12 : 12V - : ADJ
Package SOP-8
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