Document
A8697 Wide Input Voltage 4.0 A Step Down Regulator
Features and Benefits
▪ 8 to 25 V input range ▪ Integrated DMOS switch ▪ Adjustable fixed off-time ▪ Adjustable output
Package: 8-Lead SOIC with exposed thermal pad (suffix LJ)
Description
The A8697 is a constant off-time current mode step-down regulator with a wide input voltage range. Regulation voltage is set by external resistors, to output voltages as low as 0.8 V.
The A8697 includes an integrated power DMOS switch to reduce the total solution footprint. It also features internal compensation, allowing users to design stable regulators with minimal design efforts.
The off-time can be set with an external resistor, allowing flexibility in inductor selection. Additionally, the A8697 has a logic level enable pin which can shut the device down and put it into a low quiescent current mode for power sensitive applications.
The A8697 is supplied in a low-profile 8-lead SOIC with exposed pad (package LJ). Applications include:
▪ Applications with 8 to 25 V input ▪ Consumer electronics, networking equipment ▪ 12 V lighter-powered applications (portable DVD, etc.) ▪ Point of Sale (POS) applications
Approximate Scale 1:1
Typical Application
CBOOT 0.01 μF
VIN +12 V
+ CIN
47 μF 25 V
BOOT
VIN
ENB
LX
A8697
TSET RTSET 51.1 k7
GND
VBIAS FB
Ratings: L: CDRH104R-3R8 COUT: EEUFM1V151 CIN: EEVFC1H470P
L 3.8 μH
D1
R1
2 k7
R2 6.14 k7
Circuit for 12 V step down to 1.06 V at 4 A
VOUT 1.06 V/ 4.0 A
+
COUT 150 μF 56 mΩ
Efficiency (%)
Efficiency versus Load Current
90
80
VOUT = 2.5 V
70 VOUT = 1.8 V
60 VOUT = 1.06 V
50
40
30
20
10
0
0
1
2
3
4
Load Current (A)
Efficiency curve for circuit at left
A8697-DS, Rev. 3
A8697
Wide Input Voltage 4.0 A Step Down Regulator
Absolute Maximum Ratings
Characteristic
Symbol
Conditions
Min.
Typ.
Max. Units
VIN Supply Voltage
VIN
–
–
25
V
VBIAS Input Voltage
VBIAS
–0.3
–
7
V
Switching Voltage
VS
–1
–
–
V
ENB Input Voltage
VENB
–0.3
–
7
V
Operating Ambient Temperature Range
TA
Range E
–40
–
85
°C
Junction Temperature
TJ(max)
–
–
150
°C
Storage Temperature
TS
–55
–
150
°C
*Output current rating may be limited by duty cycle, ambient temperature, and heat sinking. Under any set of conditions, do not exceed the specified current ratings, or a junction temperature, TJ, of 150°C.
Package Thermal Characteristics*
Package
RθJA (°C/W)
PCB
LJ
35
4-layer
* Additional information is available on the Allegro website.
Ordering Information
Use the following complete part numbers when ordering:
Part Numbera
Packingb
A8697ELJTR-T
13 in. reel, 3000 pieces/reel
aLeadframe plating 100% matte tin. bContact Allegro for additional packing options.
Description
LJ package, SOIC surface mount with exposed thermal pad
Allegro MicroSystems, LLC
2
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
A8697
Wide Input Voltage 4.0 A Step Down Regulator
Functional Block Diagram
BOOT VIN
ENB μC
TSET
GND VBB UVLO TSD
Boot Charge
–
+
Switch Disable
Switch PWM Control
+
I_Peak
Clamp
–
I_Demand
–
Error
COMP
+
VIN
VIN
LX L1
D1
VOUT ESR COUT
FB Bias Supply
VBIAS
Soft Start Ramp Generation
0.8 V
Allegro MicroSystems, LLC
3
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
A8697
Wide Input Voltage 4.0 A Step Down Regulator
ELECTRICAL CHARACTERISTICS1,2 at TA = 25°C, VIN = 8 to 25 V (unless noted otherwise)
Characteristics
Symbol
Test Conditions
Min.
VENB = LOW, VIN = 12 V, VBIAS = 3.2 V, VFB = 1.5 V (not switching)
–
VIN Quiescent Current
IVIN(Q)
VENB = LOW, VIN = 12 V, VBIAS < 3 V, VFB = 1.5 V
–
VENB = HIGH
–
VBIAS Input Current
IBIAS
VBIAS = VOUT
–
Buck Switch On Resistance
RDS(on)
TA = 25°C, IOUT = 3 A
–
Fixed Off-Time Proportion
Based on calculated value
–15
Feedback Voltage
VFB
0.784
Output Voltage Regulation
VOUT
IOUT = 0 mA to 3 A
–3
Feedback Input Bias Current
IFB
–400
Soft Start Time
tss
5
Buck Switch Current Limit
ICL
VFB > 0.4 V VFB < 0.4 V
4.8 –
ENB Open Circuit Voltage
VOC
Output disabled
2.0
ENB Input Voltage Threshold
VENB(0) LOW level input (Logic 0), output enabled
–
ENB Input Current
IENB(0)
VENB = 0 V
–10
VIN Undervoltage Threshold
VUVLO
VIN rising
6.6
VIN Undervoltage Hysteresis
VUVLO(hys) VIN falling
0.7
Thermal Shutdown Temperature
TJTSD
Temperature increasing
–
Thermal Shutdown Hysteresis
TJTSD(hys) Recovery = TJTSD – TJTSD(hys)
–
1Negative current is defined as coming out of (sourcing) the specified device pin. 2Specifications over the junction temperature range of 0ºC to 125ºC are assured by design and characterization.
Typ.
1.0
4.1
– 3.8 180 – 0.8 – –100 10 6.2 2.7 – – – 6.9 – 165 15
Max.
–
–
100 5 – 15
0.816 3
100 15 7.2 – 7 1.0 –1 7..