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ACT6390/ACT6391
Rev0, 13-May-08
1.7A/2.5A PWM Step-Up DC/DC Converters In MSOP FEATURES
* * * *
Greater than 90% Efficiency Adjustable Output Voltage Up to 12V Internal 14V Power MOSFET Two Peak Current Options:
GENERAL DESCRIPTION
The ACT6390/ACT6391 are high-performance, fixed-frequency, current-mode PWM step-up DC/DC converters that incorporate internal power MOSFETs. The ACT6390 includes an integrated 0.2 power MOSFET that supports peak currents of up to 1.7A, while the ACT6391's integrated 0.15 power MOSFET supports currents of up to 2.5A. The ACT6390 and ACT6391 both utilize simple external loop compensation and a pin-selectable fixed-frequency of either 700kHz or 1.3MHz, allowing optimization between component size, cost, and AC performance across a wide range of applications. Additional functions include an externally programmable soft-start function for easy inrush current control, internal over-voltage protection (OVP), cycle-by-cycle current limit protection, and thermal shutdown. Both the ACT6390 and the ACT6391 are available in the small 8-pin MSOP-8 package.
- ACT6390: 1.7A, 0.2 - ACT6391: 2.5A, 0.15 * Selectable 700kHz/1.3MHz Frequency
* * * * * * * * *
Integrated Over-Voltage Protection (OVP) Programmable Soft-Start Function Thermal Shutdown Cycle-by-Cycle Over-Current Protection Small MSOP-8 Package
APPLICATIONS
TFT LCD Monitors Battery-Powered Equipment Set-Top Boxes DSL and Cable Modems and Routers
SIMPLIFIED APPLICATION CIRCUIT
VIN 2.7V to 5.5V IN
ON OFF 1.3MHz 700kHz
EN
ACT6390 ACT6391
SW R1 FB G R2 VOUT
FREQ SS COMP
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ACT6390/ACT6391
Rev0, 13-May-08
ORDERING INFORMATION
PART NUMBER
ACT6390MH-T ACT6391MH-T
CURRENT LIMIT
1.7A 2.5A
TEMPERATURE RANGE
-40C to 85C -40C to 85C
PACKAGE
MSOP-8 MSOP-8
PINS
8 8
PACKAGING
TAPE & REEL TAPE & REEL
PIN CONFIGURATION
COMP FB EN G 1 2 3 4 8 SS FREQ IN SW
ACT6390 ACT6391
7 6 5
MSOP-8
PIN DESCRIPTIONS
PIN
1 2 3 4 5 6 7 8
NAME
COMP FB EN G SW IN FREQ SS
DESCRIPTION
Error Amplifier Compensation Node. Connect to a resistor RC and capacitor CC in series to ground. Feedback Input. Connect this pin a resistor divider from the output to set the output voltage. FB is regulated to 1.24V. Enable Control. Connect to a logic high level to enable the IC. Connect to a logic low level to disable the IC. When unused, connect EN pin to IN (do not leave pin floating). Ground. Switch Output. Connect this pin to the inductor and the schottky diode. To minimize EMI, minimize the PCB trace path between this pin and the input bypass capacitor. Supply Input. Bypass to G with a 1F or larger capacitor. Frequency Setting Pin. A logic low sets the switching frequency at 700kHz. A logic high sets the switching frequency at 1.3MHz. This pin has an internal 5.5A pull-down current. Soft Start Control Input. Connect a capacitor from this pin to G to set soft-start timing duration (tSS = 2.2 x 105 x CSS). SS is discharged to ground in shutdown. SS may be left unconnected if soft start is not desired.
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ACT6390/ACT6391
Rev0, 13-May-08
ABSOLUTE MAXIMUM RATINGS
PARAMETER
SW to G IN, EN, FB, FREQ, COMP to G SS to G Continuous SW Current Junction to Ambient Thermal Resistance (JA) Maximum Power Dissipation Operating Junction Temperature Storage Temperature Lead Temperature (Soldering, 10 sec)
VALUE
-0.3 to 14 -0.3 to 6 -0.3 to VIN + 0.3 Internally Limited 200 0.5 -40 to 150 -55 to 150 300
UNIT
V V V A C/W W C C C
: Do not exceed these limits to prevent damage to the device. Exposure to absolute maximum rating conditions for long periods may affect device reliability.
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ACT6390/ACT6391
Rev0, 13-May-08
ELECTRICAL CHARACTERISTICS
(VIN = VEN = 3V, VFREQ = 0V, TA = 25C, unless otherwise specified.)
PARAMETER
Switch Voltage Rating Input Voltage Under Voltage Lockout Threshold Under Voltage Lockout Hysteresis VIN Rising
TEST CONDITIONS
MIN
TYP
MAX 12
UNIT V V V mV
2.7 2.2 2.35 65 VFB = 1.3V, Not Switching 0.2 ACT6390 ACT6391 1 1.4 0.1 490 900 80 700 1300 86 86 1.22 VFB = 1.27V VFB from 2.6V to 5.5V I = 5A VFB = 1.15V and 1.35V, VCOMP = 1.1V VFB = 1V, Duty Cycle = 65% ACT6390 ACT6391 VSW = 12V, EN = G ACT6390 ACT6391 VSS = 1.2V VSS = 1.2V, VEN = 0V EN, FREQ EN, FREQ VEN = 0V or 5V VFREQ = 3V 2.5 0 5.5 160 20 1.4 2 0.45 0.3 4.5 110 ACT6390 ACT6391 1.2 1.8 70 1.24 0 0.05 150 11 1.7 2.5 0.2 0.15
5.5 2.5
0.35 4 4 10 910 1700 92 A kHz kHz % V nA %/V s A 2.3 3.4 0.4 0.3 15 A mA
Quiescent Supply Current
VFB = 1.0V, Switching EN = G FREQ = G FREQ = IN FREQ = G FREQ = IN
Supply Current in Shutdown Switching Frequency
Maximum Duty Cycle FB Feedback Voltage FB Input Current FB Voltage Line Regulation Error Amplifier Trans-conductance Error Amplifier Output Current Switch Current Limit
1.26 80 0.15 240
Switch On Resistance Switch Leakage Current Current Sense Trans-resistance Soft Start Pin Bias Current Soft Start Reset Resistance Logic High Threshold Logic Low Threshold EN Input Current FREQ Pull-down Current Thermal Shutdown Temperature Thermal Shutdown Hysteresis
A V/A
7 220
A V
0.4 1 8.5
V A A C C
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ACT6390/ACT6391
Rev0, 13-May-08
FUNCTIONAL BLOCK DIAGRAM
EN 4.5A COMP ERROR AMPLIFIER FB 1.24V ERROR COMPARATOR SOFT START SS IN
SW CONTROL AND DRIVE LOGIC
FREQ
OSCILLATOR 5.5A
CURRENT SENSE AMPLIFIER
FUNCTIONAL DESCRIPTION
The ACT6390 and ACT6391 are highly efficient step-up DC/DC converters that employ a currentmode, fixed frequency pulse-width modulation (PWM) architecture with excellent line and load regulation. The ACT6390 and ACT6391 operate at constant switching frequency under medium to high load current conditions. At light loads, these devices operate in a pulse-skipping mode in order to improve light-load efficiency.
t SS = 2 . 2 x 10 5 x C SS
Frequency Selection
The ACT6390 and ACT6391 include a pinselectable operating frequency drive FREQ to a logic high for 1.3MHz operation, drive FREQ to a logic low for 700kHz operation. Selectable operating frequency, in combination with the external compensation network, allows a wide range of flexibility in optimizing total solution size and cost. FREQ is internally pulled down by 5.5A, this pin may be left unconnected to achieve a 700kHz operating frequency.
Soft-Start
The ACT6390 and ACT6391 both offer a programmable soft-start function which minimizes inrush current during startup. The soft-start period is programmed by connecting a capacitor (CSS) between SS and G. Operation of the soft-start function is as follows: when the IC is disabled, SS is actively discharged to G. Upon enabling the IC, CSS is charged with a 4.5A current so that the voltage at SS increases in a controlled manner. The peak inductor current is limited by the voltage at SS, so that the input current is limited until the soft-start period expires, and the regulator can achieve its full output current rating. The soft-start period can be calculated as a simple function of the soft-start capacitor using the equation:
Setting the Output Voltage
The ACT6390 and ACT6391 both feature external adjustable output voltages of up to 12V. To program the output voltage, simply connect a resistive voltage divider between the output, FB, and G, with resistors set according to the following equation:
V R1 = R 2 x OUT VFB
Where VFB is 1.24V.
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SLOPE COMPENSATION
+
+
+
CLOCK
+
-
-
G
(1)
- 1
(2)
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ACT6390/ACT6391
Rev0, 13-May-08
Inductor Selection
As a step-up converter, the switch duty cycle (D) is determined by the input voltage (VIN) and output voltage (VOUT), as given by the following formula:
L > LMIN =
(VOUT - VIN ) x RCS
1.75 x fSW
(10)
D=
VOUT - VIN VOUT
(3)
Where RCS is the current sense trans-resistance, RCS is 0.45 for ACT6390, and RCS = 0.3 for ACT6391. For example: VIN = 3.3V, VOUT = 12V, fSW = 700kHz IOUT = 250mA, = 85%, FREQ = G, K = 0.4
Define
K=
IL I L (DC )
(4)
V L = IN V OUT
2
VOUT - VIN I xf x K OUT SW
(11)
Where: IL is the inductor ripple current in steady state, typically chosen to be about 0.3, and
0.85 3.3V 12V - 3.3V = x 7.99H 12V 250mA x700kHz 0.4
Select L = 10H Assuming the minimum input voltage is 3V and low cost external components are used, yielding a low efficiency of just 80%.
2
IL =
VIN V xD DT = IN L L x fSW
(5)
IL(DC) is the inductor DC current, given by:
IL (DC ) =
VOUT x IOUT VIN x
(6)
IL (DC ,MAX ) =
IL (MAX ) =
250 mA x12V = 1.25 A 3V x 0.8
(12) (13) (14)
Where is typical efficiency. Solving equations (3),(4),(5) and (6) for the inductor value,
3V x (12V - 3V ) = 0.32 A 12V x10 H x 700 kHz
V L = IN V OUT
(VOUT - VIN ) x I xf OUT SW K
2
(7)
IPEAK (MAX ) = 1.25 A +
1 0.32 A = 1.41A 2
For stability,
This equation can be used to determine the correct trade-off between efficiency, current ripple, size and cost. When selecting an inductor make sure that the inductors maximum DC current and saturation current exceed the maximum operation point, calculated by: I xV IL (DC ,MAX ) = OUT (MAX ) OUT (8) VIN (MIN ) x and
1 IL(PEAK ,MAX ) = IL(DC,MAX ) + IL(MAX ) 2 IOUT (MAX ) xVOUT 1 VIN (MIN ) [VOUT -VIN (MIN ) ] = +x (9) VIN (MIN ) x 2 VOUT x L x fSW
LMIN =
(12V - 3.3V ) x 0.45 = 3.2 H
1.75 x 700kHz
(15)
Which meets the slope compensation requirement.
Loop Compensation
REF FB 2 + EA GM COMP 3
RCOMP CCOMP2 CCOMP
If the output voltage is greater than two times of input voltage, that means the duty cycle is greater than 50%, the slope compensation is required for stability. When operating in this condition ensure that the inductor value is greater than LMIN:
The ACT6390 and ACT6391 feature a simple loop compensation scheme. Simple follow the procedure detailed below to determine suitable compensation components. For best results be sure to prototype to confirm the values, and adjust the compensation network (by inspecting the transient response, for example) as needed to optimize results for your particular application. When the converter operates with continuous inductor current, a right-half-plane zero exits in the loop's gain-frequency response. To ensure stability,
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ACT6390/ACT6391
Rev0, 13-May-08 the cross-over frequency (unity gain-frequency) should be less than one-fifth of the right-half-plane zero fZ(RHP), and lower than one-fifteenth of switching frequency fsw. CCOMP2,
CCOMP2 = COUT x RESR RCOMP
(23)
fZ (RHP ) =
VIN x R LOAD 2 2VOUT x x L
2
(16)
If the value of CCOMP2 calculated by (23) is smaller than 10pF, CCOMP2 can be omitted. For example:
Choose fC =
1 fZ (RHP ) , then calculate CCOMP: 5
CCOMP
R V G = FB x LOAD x M (1 - D ) VOUT RCS 2fC = VIN x VFB RLOAD x GM x 2 RCS x 2fC VOUT
(17)
fZ (RHP)
12V 250mA 57.8kHz = 2 2 x (12V ) x x10 H
1 fZ (RHP ) = 11.56 kHz 5
(3.3V )2 x
(24)
Choose fC =
CCOMP =
Select RCOMP to meet the transient-droop requirements.
3.3V x1.24 V 48 150S x x = 6.26nF (25) 2 0.45 2 x11.56kHz (12V )
V xI K xVFB x GM x RCOMP = RCS x OUT OUT x 1 + VIN x 2
RCOMP K RCS x VOUT x IOUT 1 + 2 = x VFB x GM x VIN x
Choose CCOMP = 6.8nF Assume that 200mV of transient droop can be accepted:
(18)
=
(19)
200 mV 1 = 60 12V
(26)
Where: is the transient droop percentage which can be accepted, calculated by:
=
VOUT VOUT
0.4 0.45 x12V x 250mA1 + 2 RCOMP = = 186.3k (27) 1 x1.24V x150S x 3.3V x 0.85 60 Choose RCOMP = 180k
(20)
COUT =
K: is defined in equation (4) : is the typical efficiency. VFB: is the feedback voltage, 1.24V GM: is the trans-conductance of the error amplifier. The output capacitor is chosen to set the output pole for canceling the RCOMP, CCOMP zero.
RCOMP x CCOMP 180k x 6.8nF = = 25.5 F (28) RLOAD 12V 0.25 A
COUT can be chosen to be either 22F or 33F, choose 33F to reduce droop.
RCOMP =
RLOAD x COUT 48 x 33F = = 233k CCOMP 6.8nF
(29)
COUT =
RCOMP x CCOMP RLOAD
If a ceramic capacitor is used with an assumed ESR of 20m,
(21)
fZ (ESR ) =
CCOMP2 is optional and can be used when the output capacitor has significant ESR. The ESR will form a zero as follows:
1 = 241kHz 2 x 33 F x 20 m
(30)
fZ(ESR) > fC Since the zero frequency is greater than the pole frequency ,CCOMP2 can be omitted. If a tantalum capacitor is used, whose ESR is about 0.5,
fZ (ESR ) =
1 2 x RESR x COUT
(22)
If this zero occurs at a higher frequency than the cross-over frequency, it can be ignored. Otherwise, it should be canceled with the pole set by capacitor
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ACT6390/ACT6391
Rev0, 13-May-08
fZ (ESR) =
1 = 9.64kHz 2 x 33F x 0.5
(31)
fZ(ESR) < fC
RESR x COUT 0.5 x 33F = = 70.8 pF RCOMP 233k Choose CCOMP2 = 82pF CCOMP2 =
(32)
Rectifier Selection
For optimal performance, the rectifier should be a Schottky rectifier that is rated to handle both the output voltage as well as the peak switch current.
Over Voltage Protection
The ACT6390 and ACT6391 both feature internal automatic over-voltage protection (OVP). Once the outputs achieve regulation, if the voltage at FB falls below 0.125V the controller will automatically disable and latch off, preventing the controller from running open-loop and potentially damaging the IC and load. To re-enable the converters, simply cycle the EN pin or remove and reapply power to the input.
Shutdown
Drive EN low to disable the IC and reduce the supply current to just 0.1A. As with all nonsynchronous step-up DC/DC converters, the external Schottky diode provides a DC path from the input to the output in shutdown. As a result, the output drops to one diode voltage drop below the input in shutdown.
Thermal Shutdown
The ACT6390 and ACT6391 both feature integrated thermal overload protection. Both devices are automatically disabled when their junction temperatures exceed 160C, and automatically re-enable when the die temperature decreases by 20C.
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ACT6390/ACT6391
Rev0, 13-May-08
TYPICAL PERFORMANCE CHARACTERISTICS
(VIN = VEN = 3.3V, FREQ = G, TA = 25C, unless otherwise specified.)
ACT6390 Efficiency vs. Output Current
95 90 85 VIN = 3.3V VOUT = 5V FREQ = IN L = 2.7H FREQ = G L = 5.4H 95 90 85 ACT6390-001
ACT6390 Efficiency vs. Output Current
ACT6390-002 VIN = 5V VOUT = 12V FREQ = G L = 10H FREQ = IN L = 5.4H
Efficiency (%)
80 75 70 65 60 55 50 0 10
Efficiency (%)
80 75 70 65 60 55 50
100
1000
0
10
100
1000
Output Current (mA)
Output Current (mA)
ACT6390 Efficiency vs. Output Current
95 90 85 VIN = 3.3V VOUT = 12V 0.40 ACT6390-003
ACT6390 No Load Supply Current vs. VIN
ACT6390-004
Supply Current (mA)
0.36
Efficiency (%)
80 75 70 65 60 55 50 0
FREQ = G L = 10H FREQ = IN L = 5.4H
FREQ = IN L = 5.4H
0.32
0.28
FREQ = G L = 10H
0.24
0.20 10 100 1000 2.5 3 3.5 4 4.5 5 5.5
Output Current (mA)
VIN (V)
ACT6390 Maximum Output Current vs. Input Voltage Maximum Output Current (mA)
2200 1800 1400 1000 600 200 0 2.5 3.1 3.7 4.3 4.9 5.5 VOUT = 12V ACT6390-005 FREQ = G
VOUT = 5V VOUT = 9V
Input Voltage (V)
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ACT6390/ACT6391
Rev0, 13-May-08
TYPICAL PERFORMANCE CHARACTERISTICS
(VIN = VEN = 3.3V, FREQ = G, TA = 25C, unless otherwise specified.)
ACT6391 Efficiency vs. Output Current
95 90 85 VIN = 3.3V VOUT = 9V 95 90 85 ACT6391-006 FREQ = G L = 5.4H
ACT6391 Efficiency vs. Output Current
ACT6391-007 VIN = 5V VOUT = 12V
Efficiency (%)
Efficiency (%)
80 75 70 65 60 55 50 0 10 100 FREQ = IN L = 4.7H
80 75 70 65 60 55 50 FREQ = G L = 10H
FREQ = IN L = 4.7H
1000
0
10
100
1000
Output Current (mA)
Output Current (mA)
ACT6391 Efficiency vs. Output Current
95 90 85 ACT6391-008 VIN = 3.3V VOUT = 12V FREQ = G L = 10H 0.40
ACT6391 No Load Supply Current vs. VIN
ACT6391-009 VOUT = 12V
Supply Current (mA)
0.36 0.32 FREQ = G L = 10H FREQ = IN L = 4.7H
Efficiency (%)
80 75 70 65 60 55 50 0 10 100 FREQ = IN L = 4.7H
0.28
0.24
0.20 1000 2.5 3 3.5 4 4.5 5 5.5
Output Current (mA)
VIN (V)
ACT6391 Maximum Output Current vs. Input Voltage Maximum Output Current (mA)
2400 FREQ = G 2000 1600 1200 800 400 0 2.5 3 3.5 4 4.5 5 VOUT = 12V VOUT = 5V VOUT = 9V ACT6391-010
Input Voltage (V)
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ACT6390/ACT6391
Rev0, 13-May-08
PACKAGE OUTLINE
MSOP-8 PACKAGE OUTLINE AND DIMENSIONS
b
e
C L
DIMENSION IN SYMBOL MILLIMETERS MIN MAX
A A1 0.820 0.020 0.750 0.250 0.090 2.900 2.900 4.750 1.100 0.150 0.950 0.380 0.230 3.100 3.100 5.050
DIMENSION IN INCHES MIN
0.032 0.001 0.030 0.010 0.004 0.114 0.114 0.187
MAX
0.043 0.006 0.037 0.015 0.009 0.122 0.122 0.199
E1
A2
E
b C D E
A2 D A1 A
E1 e L
0.650 TYP 0.400 0 0.800 6
0.026 TYP 0.016 0 0.031 6
Active-Semi, Inc. reserves the right to modify the circuitry or specifications without notice. Users should evaluate each product to make sure that it is suitable for their applications. Active-Semi products are not intended or authorized for use as critical components in lifesupport devices or systems. Active-Semi, Inc. does not assume any liability arising out of the use of any product or circuit described in this datasheet, nor does it convey any patent license. Active-Semi and its logo are trademarks of Active-Semi, Inc. For more information on this and other products, contact sales@activesemi.com or visit http://www.active-semi.com. For other inquiries, please send to: 1270 Oakmead Parkway, Suite 310, Sunnyvale, California 94085-4044, USA
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