View MAX189_29397.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

19-2221; Rev 1; 3/04
1.4MHz SOT23 Current-Mode Step-Up DC-DC Converter MAX1896
General Description
The MAX1896 step-up DC-DC converter incorporates high-performance current-mode, fixed-frequency, pulse-width modulation (PWM) circuitry and an internal 0.7 N-channel MOSFET to provide a highly efficient regulator with fast response. High switching frequency (1.4MHz) allows fast loop response and easy filtering with small components. The MAX1896 can produce an output voltage as high as 13V from an input as low as 2.6V. Soft-start is programmable with an external capacitor, which sets the input current ramp rate. In shutdown mode, current consumption is reduced to 0.01A. The MAX1896 is available in a space-saving 6-pin SOT23 package. The ultra-small package and high switching frequency allow cost and space-efficient implementations. >90% Efficiency Adjustable Output Up to 13V Guaranteed 12V/120mA Output from 5V Input 2.6V to 5.5V Input Range LT1613 Pin Compatible 0.01A Shutdown Current Programmable Soft-Start Space-Saving 6-Pin SOT23 Package
Features
Applications
Notebook Computers LCD Displays PCMCIA Cards Portable Applications Hand-Held Devices
PART MAX1896EUT-T
Ordering Information
TEMP RANGE -40C to +85C PIN-PACKAGE 6 SOT23-6
Typical Operating Circuit
INPUT 2.6V TO 5.5V
Pin Configuration
TOP VIEW
OUTPUT UP TO 13V UP TO 600mA IN LX
LX 1
6
IN
GND 2
MAX1896
5
SS
MAX1896
R1 ON OFF SHDN SS FB GND R2
FB 3
4
SHDN
SOT23
________________________________________________________________ Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim's website at www.maxim-ic.com.
1.4MHz SOT23 Current-Mode Step-Up DC-DC Converter MAX1896
ABSOLUTE MAXIMUM RATINGS
LX to GND ..............................................................-0.3V to +14V IN, SHDN, FB to GND...............................................-0.3V to +6V SS to GND ...................................................-0.3V to (VIN + 0.3V) RMS LX Pin Current ..............................................................0.6A Continuous Power Dissipation (TA = +70C) (Note 1) 6-Pin SOT23 (derate 9.1mW/C above +70C)...........727mW Operating Temperature Range ...........................-40C to +85C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) .................................+300C
Note 1: Thermal properties are specified with product mounted on PC board with one square-inch of copper area and still air.
Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(VIN = VSHDN = 3V, FB = GND, SS = open, TA = 0C to +85C, unless otherwise noted.)
PARAMETER Input Supply Range Output Voltage Adjust Range VIN Undervoltage Lockout Quiescent Current Shutdown Supply Current ERROR AMPLIFIER Feedback Regulation Set Point FB Input Bias Current Line Regulation OSCILLATOR Frequency Maximum Duty Cycle POWER SWITCH Current Limit (Note 2) On-Resistance Leakage Current SOFT-START Reset Switch Resistance Charge Current CONTROL INPUT Input Low Voltage Input High Voltage SHDN Input Current VIL VIH ISHDN V SHDN, VIN = 2.6V to 5.5V V SHDN, VIN = 2.6V to 5.5V V SHDN = 3V V SHDN = 0 1.0 25 0.01 50 0.1 0.3 V V A VSS = 1.2V 1.5 4 100 7.0 A ILIM RON ILXOFF VLX = 12V, TA = +25C VLX = 12V VFB = 1V, duty cycle = 50% 0.55 0.8 0.7 0.1 1 1 10 A A fOSC DC 1000 82 1400 86 1800 kHz % VFB IFB VFB = 1.24V 2.6V < VIN < 5.5V 1.2 1.24 21 0.05 1.25 80 0.20 V nA %/V SYMBOL VIN VOUT UVLO IIN Circuit of Figure 1 VIN rising, 50mV hysteresis VFB = 1.3V, not switching VFB = 1.0V, switching V SHDN = 0, TA = +25C V SHDN = 0 2.25 2.4 0.2 1 0.01 0.01 CONDITIONS MIN 2.6 TYP MAX 5.5 13 2.55 0.4 5 0.5 10 UNITS V V V mA A
2
_______________________________________________________________________________________
1.4MHz SOT23 Current-Mode Step-Up DC-DC Converter
ELECTRICAL CHARACTERISTICS
(VIN = VSHDN = 3V, FB = GND, SS = open, TA = -40C to +85C, unless otherwise noted.) (Note 3)
PARAMETER Input Supply Range Output Voltage Adjust Range VIN Undervoltage Lockout Quiescent Current Shutdown Supply Current ERROR AMPLIFIER Feedback Regulation Set Point FB Input Bias Current Line Regulation OSCILLATOR Frequency Maximum Duty Cycle POWER SWITCH Current Limit (Note 2) On-Resistance Leakage Current SOFT-START Reset Switch Resistance Charge Current CONTROL INPUT Input Low Voltage Input High Voltage SHDN Input Current VIL VIH I SHDN VSS = 1.2V V SHDN = VIN = 2.6V to 5.5V V SHDN = VIN = 2.6V to 5.5V V SHDN = 3V V SHDN = 0 1.0 50 0.1 1.25 ILIM RON ILXOFF VLX = 12V VFB = 1V, duty cycle = 50% 0.55 1 10 100 7.50 0.3 A A A V V A fOSC DC 1000 82 1800 kHz % VFB IFB VFB = 1.24V 2.6V < VIN < 5.5V 1.2 1.25 80 0.20 V nA %/V SYMBOL VIN VOUT UVLO IIN Circuit of Figure 1 VIN rising, 50mV hysteresis. VFB = 1.3V, not switching VFB = 1.0V, switching V SHDN = 0 2.25 CONDITIONS MIN 2.6 TYP MAX 5.5 13 2.55 0.4 5 10 UNITS V V V mA A
MAX1896
Note 2: Current limit varies with duty cycle due to slope compensation. See the Output Current Capability section. Note 3: Specifications to -40C are guaranteed by design and not production tested.
_______________________________________________________________________________________
3
1.4MHz SOT23 Current-Mode Step-Up DC-DC Converter MAX1896
Typical Operating Characteristics
(Circuit of Figure 1, VIN = 3.3V, TA = +25C, unless otherwise noted.)
EFFICIENCY vs. OUTPUT CURRENT
MAX1896 toc01
EFFICIENCY vs. OUTPUT CURRENT
MAX1896 toc02
EFFICIENCY vs. OUTPUT CURRENT
MAX1896 toc03
100
100
100
90 EFFICIENCY (%)
90 EFFICIENCY (%)
90 EFFICIENCY (%)
80
80
80
70
70
70
60
VIN = 3.3V, VOUT = 5V, CIRCUIT OF FIGURE 1 1 10 100 1000
60
VIN = 3.3V, VOUT = 13V, CIRCUIT OF FIGURE 3 1 10 100 1000
60
VIN = 5V, VOUT = 13V, CIRCUIT OF FIGURE 3 1 10 100 1000
50 OUTPUT CURRENT (mA)
50 OUTPUT CURRENT (mA)
50 OUTPUT CURRENT (mA)
NO LOAD SUPPLY CURRENT vs. INPUT VOLTAGE
MAX1896 toc04
OUTPUT VOLTAGE vs. OUTPUT CURRENT
CIRCUIT OF FIGURE 3
MAX1896 toc05
LOAD TRANSIENT (VOUT = 13V)
MAX1896 toc06
2.0 NO LOAD SUPPLY CURRENT (mA)
13.10
1.5
OUTPUT VOLTAGE (V)
13.05 TA = +25C 13.00
LOAD CURRENT 100mA/div OUTPUT VOLTAGE AC-COUPLED 200mV/div
1.0
0.5
VOUT = 13V, CIRCUIT OF FIGURE 3
12.95 TA = -40C 12.90
TA = +85C
0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 INPUT VOLTAGE (V)
INDUCTOR CURRENT 500mA/div 200 200s/div CFF = 100pF, COUT = 0.1F CERAMIC + 10F CERAMIC
0
50
100
150
OUTPUT CURRENT (mA)
LOAD TRANSIENT (VOUT = 5V)
MAX1896 toc07
STARTUP WAVEFORM WITHOUT SOFT-START
MAX1896 toc08
STARTUP WAVEFORM WITH SOFT-START
IOUT = 10mA SHDN 5V/div OUTPUT VOLTAGE 5V/div
MAX1896 toc09
LOAD CURRENT 200mA/div OUTPUT VOLTAGE AC-COUPLED 200mV/div
SHDN 5V/div
OUTPUT VOLTAGE 5V/div INDUCTOR CURRENT 500mA/div
INDUCTOR CURRENT 500mA/div 400s/div COUT = 0.1F CERAMIC + 22F TANTALUM
INDUCTOR CURRENT 500mA/div 100s/div VIN = 3.3V, COUT = 0.1F CERAMIC + 3.3F TANTALUM CIRCUIT OF FIGURE 3 2ms/div VIN = 3.3V, CSS = 33nF, COUT = 3.3F TANTALUM + 0.1F CERAMIC CIRCUIT OF FIGURE 3
4
_______________________________________________________________________________________
1.4MHz SOT23 Current-Mode Step-Up DC-DC Converter MAX1896
Typical Operating Characteristics (continued)
(Circuit of Figure 1, VIN = 3.3V, TA = +25C, unless otherwise noted.)
STARTUP WAVEFORM WITH SOFT-START
IOUT = 100mA SHDN 5V/div OUTPUT VOLTAGE 5V/div
MAX1896 toc10
SWITCHING WAVEFORM
MAX1896 toc11
MAXIMUM OUTPUT CURRENT vs. INPUT VOLTAGE
MAX1896 toc12
600 MAXIMUM OUTPUT CURRENT (mA) 500 400 300 200 100 0 MAXIMUM OUTPUT CURRENT DEFINED AT 90% OF NO LOAD OUTPUT VOLTAGE 2.5 3.0 3.5 4.0 4.5 5.0 VOUT = 5V VOUT = 12V
LX VOLTAGE 5V/div
OUTPUT VOLTAGE AC-COUPLED 200mV/div INDUCTOR CURRENT 500mA/div 2ms/div VIN = 3.3V, CSS = 33nF, COUT = 3.3F TANTALUM + 0.1F CERAMIC CIRCUIT OF FIGURE 3 400ns/div VIN = 5V, COUT = 0.1F CERAMIC + 2.2F CERAMIC
INDUCTOR CURRENT 500mA/div
IOUT = 150mA
5.5
INPUT VOLTAGE (V)
Pin Description
PIN 1 2 3 NAME LX GND FB FUNCTION Power Switching Connection. Connect LX to the inductor and output rectifier. Connect components as close to LX as possible. Ground Feedback Input. Connect a resistive voltage-divider from the output to FB to set the output voltage. See the Setting the Output Voltage section. Shutdown Input. Drive SHDN low to turn off the converter. To automatically start the converter, connect SHDN to IN. Drive SHDN with a slew rate of 0.1V/s or greater. Do not leave SHDN unconnected. SHDN draws up to 50A. Soft-Start Input. Connect a soft-start capacitor from SS to GND to soft-start the converter. Leave SS open to disable the soft-start function. See the Soft-Start section. Internal Bias Voltage Input. Connect IN to the input voltage source. Bypass IN to GND with a 1F or greater capacitor as close to IN as possible.
4
SHDN
5 6
SS IN
_______________________________________________________________________________________
5
1.4MHz SOT23 Current-Mode Step-Up DC-DC Converter MAX1896
Detailed Description
The MAX1896 is a highly efficient power supply that employs a current-mode, fixed-frequency pulse-width modulation (PWM) architecture for fast-transient response and low-noise operation. The functional diagram is shown in Figure 2. As the load varies, the error amplifier sets the inductor peak current necessary to supply the load and regulate the output voltage. To maintain stability at high duty cycle, a slope-compensation signal is internally summed with the current-sense signal. At light loads, this architecture allows the MAX1896 to skip cycles to prevent overcharging the output voltage. In this region of operation, the inductor ramps up to a peak value of about 100mA, discharges to the output and waits until another pulse is needed again.
Soft-Start
The MAX1896 can be programmed for soft-start upon power-up with an external capacitor. When the MAX1896 is turned on, the soft-start capacitor (CSS) is charged at a constant current of 4A, ramping up to 0.5V. During this time, the SS voltage directly controls the peak-inductor current, allowing 0A at VSS = 0.5V to the full current limit at VSS = 1.5V. The maximum load current is available after the soft-start cycle is completed. When the MAX1896 is turned off, the soft-start capacitor is internally discharged to ground.
Shutdown
The MAX1896 shuts down to reduce the supply current to 0.01A when SHDN is low. In this mode, the internal reference, error amplifier, comparators, biasing circuit, and N-channel MOSFET are turned off. The step-up converter's output is still connected to IN via the external inductor and output rectifier.
Output-Current Capability
The output-current capability of the MAX1896 is a function of current limit, input voltage, and inductor value. Because of the slope compensation used to stabilize the feedback loop, the duty cycle affects the current limit. The output-current capability is governed by the following equation: IOUT(MAX) = (ILIM x (1.45 - 0.9 x Duty)) VIN xx VOUT where: ILIM = current limit specified at 50% (see Electrical Characteristics) DUTY = DUTY CYCLE = VOUT - VIN + VDIODE VOUT - ILIM x RON + VDIODE VDIODE = catch diode forward drop at ILIM, (V) fOSC = oscillator frequency, (Hz) L = inductor value, (H) = conversion efficiency, 0.85 nominal VIN = input voltage, (V) VOUT = output voltage, (V)
-
Applications Information
The MAX1896 operates well with a variety of external components. The components in Figure 1 are suitable for most applications. See the following sections to optimize external components for a particular application.
0.5 x Duty x VIN fOSC x L
Inductor Selection
Inductor selection depends on input voltage, output voltage, maximum current, size, and availability of inductor values. Other factors can include efficiency and ripple voltage. Inductors are specified by their inductance (L), peak current (IPK), and resistance (RL). The following step-up circuit equations are useful in choosing the inductor values based on the application. They allow the trading of peak current and inductor value while considering component availability and cost. The equation used here assumes a constant LIR, which is the ratio of the inductor peak-to-peak AC current to average DC inductor current. A good compromise between the size of the inductor versus loss and output ripple is to choose an LIR of 0.3 to 0.5. The peak inductor current is then given by: IOUT(MAX) x VOUT LIR IPK = x 1 + x VIN(MIN) 2 where: IOUT(MAX) = maximum output current, (A) VIN(MIN) = minimum input voltage, (V)
6
_______________________________________________________________________________________
1.4MHz SOT23 Current-Mode Step-Up DC-DC Converter
The inductance (H) value is then given by: L= [VIN(MIN)2 x x (VOUT VOUT
2
-
Setting the Output Voltage
The MAX1896 operates with an adjustable output from VIN to 13V. Connect a resistive voltage-divider from the output to FB (see Typical Operating Circuit). Choose a value for R2 between 10k and 50k. Calculate R1 using the equation: V R1 = R2 x OUT VFB
-1
MAX1896
VIN(MIN) )]
x LIR x IOUT(MAX) x fOSC
Diode Selection
The output diode should be rated to handle the output voltage and the peak switch current. Make sure the diode's peak current rating is at least IPK and that its breakdown voltage exceeds VOUT. Schottky diodes are recommended. If a junction rectifier is used, it must be an ultra-fast type (trr < 50ns) to prevent excessive loss in the rectifier.

where VFB, the step-up regulator feedback set point, is 1.24V. Connect the resistive-divider as close to the IC as possible.
Input and Output Capacitor Selection
The MAX1896 operates with both tantalum and ceramic output capacitors. When using tantalum capacitors, the zero caused by the ESR of the tantalum is used to ensure stability. When using ceramic capacitors, the zero due to the ESR will be at too high a frequency to be useful in stabilizing the control loop. When using ceramic capacitors, use a feedforward capacitor to increase the phase margin, improving the control-loop stability. Figure 3 shows the circuit with ceramic capacitors and the feedforward capacitor, CFF. Use the following equation to determine the value of the feedforward capacitor: C k1 x VOUT 2 CFF = x OUT R1 VIN where: x F k1 = 7.14 x 10-4 with units of A R1 = see Figure 3, () COUT = total output capacitance including any bypass capacitor on the output bus, (Farads). See Figure 3. VOUT = output voltage, (V) VIN = input voltage, (V).
0.5 0.5
Soft-Start Capacitor
The soft-start capacitor should be large enough that the current limit does not reach final value before the output has reached regulation. Calculate CSS to be: CSS > k 2 x COUT x VOUT 2 - VIN x VOUT VIN x IINRUSH - IOUT x VOUT
where: k2 = 21 x 10-6, (S) VOUT = maximum output voltage, (V) IINRUSH = peak inrush current allowed, (A) IOUT = maximum output current during power-up stage, (A) VIN = minimum input voltage, (V) The soft-start duration (tSS) is the time it takes the current limit to reach its final value. The soft-start duration can be calculated by the equation: tss = k3 CSS where: k3 = 6.67 105
_______________________________________________________________________________________
7
1.4MHz SOT23 Current-Mode Step-Up DC-DC Converter MAX1896
Application Circuits
1-Cell to 3.3V SEPIC Power Supply Figure 4 shows the MAX1896 in a single-ended primary inductance converter (SEPIC) topology. This topology is useful when the input voltage can be either higher or lower than the output voltage, such as when converting a single lithium-ion (Li+) cell to a 3.3V output. L1 and L2 are two windings on a single inductor or two separate inductors. The coupling capacitor between these two windings must be a low-ESR type to achieve maximum efficiency, and must also be able to handle high ripple currents. Ceramic capacitors are best for this application.
Layout Procedure
Good PC board layout and routing are required in highfrequency switching power supplies to achieve good regulation, and stability. It is strongly recommended that the evaluation kit PC board layouts be followed as closely as possible. Refer to the MAX1896 EV kit for a good layout. Place power components as close together as possible, keeping their traces short, direct, and wide. Avoid interconnecting the ground pins of the power components using vias through an internal ground plane. Instead, keep the power components close together and route them in a star ground configuration using component side copper, then connect the star ground to internal ground using multiple vias.
VIN 2.6V TO 4.5V L 10H SUMIDA CD43-100 IN ON/OFF
SHDN
Chip Information
CIN C1 10F 10V C2 0.1F
TRANSISTOR COUNT: 970
LX NIHON EC10QSO2L
VOUT 5V
MAX1896
0.1F
COUT 22F 16V
GND
SS CSS 33nF
FB
R1 36k R2 12k
Figure 1. Typical Application Circuit
8
_______________________________________________________________________________________
1.4MHz SOT23 Current-Mode Step-Up DC-DC Converter MAX1896
ENABLE COMPARATOR BIAS ENABLE TRANSCONDUCTANCE ERROR AMPLIFIER FB 1.24V CLOCK GND OSCILLATOR SLOPE COMPENSATION CURRENT SENSE SOFTSTART SS 4A IN
SHDN
ERROR COMPARATOR CONTROL AND DRIVER LOGIC N
LX
MAX1896
Figure 2. Functional Diagram
VIN 2.6V TO 5.5V 10F CERAMIC D1 NIHON EC10QSO2L COUT 10F CERAMIC CFF 100pF 0.1F CERAMIC
VIN 2.6V TO 5.5V
L 10H CD43-100 IN ON/OFF
SHDN
C1
LX
VOUT 13V
ON/OFF
SHDN
L1 IN LX C2 MAX1896 L2 COUT GND VOUT
MAX1896
SS CSS 33nF GND
FB
SS
R3 10k
R2 12k
R1 115k
FB
R1 R2
Figure 3. MAX1896 with Ceramic Output Capacitor and Feedforward Capacitor
Figure 4. MAX1896 in an SEPIC Configuration
_______________________________________________________________________________________
9
1.4MHz SOT23 Current-Mode Step-Up DC-DC Converter MAX1896
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information go to www.maxim-ic.com/packages.)
6LSOT.EPS
PACKAGE OUTLINE, SOT-23, 6L
21-0058
F
1
1
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
10 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2004 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

▲Up To Search▲

Price & Availability of MAX189

	To Download MAX189 Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .