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A8499 High Voltage Step-Down Regulator
Features and Benefits
▪ ▪ ▪ ▪ ▪ 8 to 50 V input range Integrated DMOS switch Adjustable fixed off-time Highly efficient Adjustable 1.2 to 24 V output
Description
The A8499 is a step down regulator that will handle a wide input operating voltage range. The A8499 is supplied in a low-profile 8-lead SOIC with exposed pad (package LJ). Applications include: ▪ Printer power supplies ▪ Consumer equipment power supplies
Package: 8-Lead SOIC with exposed thermal pad (suffix LJ)
Approximate Scale 1:1
Typical Application
+42 V
Efficiency vs. Output Current
CBOOT 0.01 μF C3 100 μF 50 V BOOT VIN C3 0.22 μF
ENB
LX
A8499
TSET
RTSET
L1 47 μH
VOUT 3.3 V / 1.2 A
VBIAS R1 17.8 kΩ
121 kΩ GND FB D1
ESR COUT 220 μF 10 V
90.0 88.0 86.0 84.0 82.0 80.0 78.0 76.0 74.0 72.0 70.0 0 200 400 600 800 1000
Efficiency %
VOUT (V) 3.3 5 1200 1400
R2 10.2 kΩ
IOUT (mA)
Circuit for 42 V step down to 3.3 V at 1.2 A. Efficiency data from circuit shown in left panel.Data is for reference only.
A8499-DS, Rev. 3
A8499
High Voltage Step-Down Regulator
Functional Block Diagram
BOOT
Boot Charge
VIN
+
VIN
–
LX D1 L1 ESR COUT µC ENB Switch Disable Switch PWM
VOUT
Clamp
TSET
+
I_Peak
–
I_Demand
– +
FB
COMP GND
Bias Supply VBIAS
VBIAS is connected to VOUT when VOUT target is between 3.3 and 5 V
UVLO TSD Soft Start Ramp Generation 1.2 V
Absolute Maximum Ratings
Supply Voltage, VIN ......................................................................... 50 V VBIAS Input Voltage, VBIAS .................................................–0.3 to 7 V Switch Voltage, VLX......................................................................... –1 V ENB Input Voltage, VENB ......................................................–0.3 to 7 V Junction Temperature, TJ(max) ....................................................... 150°C Storage Temperature, TS ............................................... –55°C to 150°C Operating Ambient Temperature, TA............................... –20°C to 85°C
Package Thermal Characteristics*
Package LJ RθJA (°C/W) 35 PCB 4-layer
* Additional information is available on the Allegro Web site
Ordering Information Use the following complete part numbers when ordering:
Part Numbera A8499SLJTR-T A8499SLJ-T
aLeadframe bContact Allegro
Packingb 13 in. reel, 3000 pieces/reel 98 pieces/tube
Description LJ package, SOIC surface mount with exposed thermal pad
plating 100% matte tin. for additional packing options.
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
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A8499
High Voltage Step-Down Regulator
ELECTRICAL CHARACTERISTICS1,2 at TA = 25°C, VIN = 8 to 50 V (unless noted otherwise)
Characteristics Symbol Test Conditions VENB = LOW, IOUT = 0 mA, VIN = 42 V VBIAS = VOUT (see note3) VIN Quiescent Current IVIN(Q) VENB = LOW, IOUT = 0 mA, VIN = 42 V VBIAS < 3 V VENB = HIGH VBIAS Input Current Buck Switch On Resistance Fixed Off-Time Proportion Feedback Voltage Output Voltage Regulation Feedback Input Bias Current Soft Start Time Buck Switch Current Limit ENB Open Circuit Voltage ENB Input Voltage Threshold ENB Input Current VIN Undervoltage Threshold VIN Undervoltage Hysteresis Thermal Shutdown Temperature Thermal Shutdown Hysteresis IFB tss ICL VOC VENB(0) IENB(0) VUVLO VUVLOHYS TJTSD ∆TJ VFB > 0.5 V VFB < 0.5 V Output disabled LOW level input (Logic 0), output enabled VENB = 0 V VIN rising VIN falling Temperature increasing Recovery = TJTSD – ∆TJ VFB IOUT = 0 mA to 2 A IBIAS RDS(on) VBIAS = VOUT TA = 25°C, IOUT = 2 A TA = 125°C, IOUT = 2 A Based on calculated value Min. – – – – – – –15 1.176 –3 –400 5 2.2 0.5 2.0 – –10 – 0.7 – – Typ. 0.90 4.4 – 3.5 700 – – 1.200 – –100 10 – – – – – 6.9 – 165 15 Max. 1.35 6.35 100 5 800 1.6 15 1.224 3 100 15 3 1.2 7 1.0 –1 7.1 1.1 – – Units mA mA μA mA mΩ Ω % V % nA ms A A V V μA V V °C °C
1. Negative current is defined as coming out of (sourcing) the specified device pin. 2. Specifications over the junction temperature range of 0ºC to 125ºC are assured by design and characterization. 3. VBIAS is connected to VOUT node when VOUT target level is between 3.3 and 5 V.
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
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A8499
High Voltage Step-Down Regulator
Functional Description
The A8499 is a fixed off-time, current-mode–controlled buck switching regulator. The regulator requires an external clamping diode, inductor, and filter capacitor, and operates in both continuous and discontinuous modes. An internal blanking circuit is used to filter out transients resulting from the reverse recovery of the external clamp diode. Typical blanking time is 200 ns. The value of a resistor between the TSET pin and ground determines the fixed off-time (see graph in the toff section). VOUT. The output voltage is adjustable from 1.2 to 24 V, based on the c.