Datasheet

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Constant-Frequency, Current-Mode

Step-Up DC/DC Controller

Data Sheet

ADP1621

Rev. B

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FEATURES

92% efficiency (no sense resistor required)

±1.0% initial accuracy

IC supply voltage range: 2.9 V to 5.5 V

Power-input voltage as low as 1.0 V

Capable of high supply input voltage (>5.5 V)

with an external NPN or a resistor

UVLO and 35 mA shunt regulator

External slope compensation with 1 resistor

Programmable operating frequency

(100 kHz to 1.5 MHz) with 1 resistor

Lossless current sensing for switch-node voltage <30 V

Resistor current sensing for switch-node voltage >30 V

Synchronizable to external clock

Current-mode operation for excellent line and load transient

responses

10 µA shutdown current

Current limit and thermal overload protection

Soft start in 2048 clock cycles

Supported by ADIsimPower™ design tool

APPLICATIONS

APD bias

Portable electronic equipment

Isolated dc/dc converter

Step-up/step-down dc/dc converter

LED driver for laptop computer and navigation system

LCD backlighting

GENERAL DESCRIPTION

The ADP1621 is a fixed-frequency, pulse-width modulation

(PWM), current-mode, step-up converter controller. It drives an

external n-channel MOSFET to convert the input voltage to a

higher output voltage. The ADP1621 can also be used to drive

flyback, SEPIC, and forward converter topologies, either isolated

or nonisolated.

The ADP1621 eliminates the use of a current-sense power

resistor by measuring the voltage drop across the on resistance

of the n-channel MOSFET. This technique, allowed up to a

maximum voltage of 30 V at the switch node, maximizes

efficiency and reduces cost. For switch-node voltages higher than

30 V or for more accurate current limiting, the CS pin can be

connected to a current-sense resistor in the source of the MOSFET.

The slope compensation is implemented by an external resistor,

allowing a wide range of external components (inductors and

MOSFETs), and can be chosen for various switching frequencies

and input and output voltages.

TYPICAL APPLICATION CIRCUIT

ADP1621

GATE

PGND

AGND

SDSN

COMP

FREQ

GND

35.7kΩ

11.5kΩ

47µF

6.3V

4.7µH

COMP

1.8nF

OUT1

1µF

10V

OSC

= 600kHz

C1 = MURATA GRM31CR60J476M

OUT3

= SANYO POSCAP 6TPE150M

L1 = TOKO FDV0630-4R7M

M1 = VISHAY Si7882DP

D1 = VISHAY SSA33L

80Ω

OUT2

10µF

10V

FREQ

31.6kΩ

OUT3

150µF

6.3V

×2

OUT

= 5V

= 3.3V

1µF

10V

0.1µF

10V

120pF

COMP

9.09kΩ

06090-001

Figure 1. High Efficiency Output Boost Converter in Lossless Mode,

3.3 V Input, 5 V Output (Bootstrapped)

100

0.01 10

LOAD CURRENT (A)

EFFICIENCY (%)

0.1 1

06090-042

Figure 2. Efficiency of Circuit Shown in Figure 1

The ADP1621 supply input voltage range is 2.9 V to 5.5 V, although

higher input voltages are possible with the use of a small-signal

NPN pass transistor or a single resistor. The voltage of the

power input can be as low as 1 V for fuel cell applications. The

switching frequency is set by an external resistor over a range of

100 kHz to 1.5 MHz and can be synchronized to an external

clock by using the SDSN pin. The shutdown quiescent current is

less than 10 µA. The ADP1621 has a thermal shutdown feature

that shuts down the gate driver when the junction temperature

reaches approximately 150°C. The internal soft start circuit limits

inrush current at startup. The ADP1621 is available in the 10-lead

MSOP lead-free package and is specified over the −40°C to +125°C

junction temperature range.

Summary of content (32 pages)

PAGE 1
FEATURES TYPICAL APPLICATION CIRCUIT VIN = 3.3V L1 4.7µH C3 1µF 10V C4 0.1µF 10V IN R1 35.7kΩ 1% RS 80Ω ADP1621 SDSN GATE COMP C2 120pF RCOMP 9.09kΩ CCOMP 1.8nF M1 COUT1 1µF 10V COUT2 10µF 10V R2 11.5kΩ 1% COUT3 150µF 6.3V ×2 PGND FREQ FB GND C1 47µF 6.3V RFREQ 31.6kΩ 1% AGND fOSC = 600kHz C1 = MURATA GRM31CR60J476M COUT3 = SANYO POSCAP 6TPE150M L1 = TOKO FDV0630-4R7M M1 = VISHAY Si7882DP D1 = VISHAY SSA33L Figure 1. High Efficiency Output Boost Converter in Lossless Mode, 3.
PAGE 2
ADP1621 Data Sheet TABLE OF CONTENTS Features .............................................................................................. 1 Duty Cycle ................................................................................... 14 Applications ....................................................................................... 1 Setting the Output Voltage ........................................................ 14 General Description .......................................................
PAGE 3
Data Sheet ADP1621 SPECIFICATIONS VIN = 5 V, RFREQ = 100 kΩ, fOSC = 200 kHz, TJ = −40°C to 125°C, unless otherwise noted. Table 1.
PAGE 4
ADP1621 Parameter GATE DRIVER GATE Rise Time 9 GATE Fall Time9 Data Sheet Symbol Conditions tR tF CGATE = 3.3 nF CGATE = 3.3 nF Min Typ 17 13 Max Unit ns ns The maximum input voltage is the shunt regulation voltage, which is typically 5.5 V and can range from 5.3 V to 6.0 V over the specified temperature range. The ADP1621 is tested in a feedback servo loop, which servos VFB to the internal reference voltage. The voltage change in FB is measured while VIN is changed from 2.9 V to 5 V.
PAGE 5
Data Sheet ADP1621 ABSOLUTE MAXIMUM RATINGS Table 2. Parameter IN to GND FB, COMP, SDSN, FREQ, GATE to GND CS to GND PIN to PGND Supply Current into IN Supply Current into PIN Storage Temperature Range Junction Operating Temperature Range1 Junction Storage Temperature Range Lead Temperature (Soldering, 10 sec) Package Power Dissipation1 Rating −0.3 V to VSHUNT −0.3 V to (VIN + 0.3 V) −5 V to +33 V −0.
PAGE 6
ADP1621 Data Sheet SIMPLIFIED BLOCK DIAGRAM VREF 1.215V ERROR AMPLIFIER SOFT START (2048 CYCLES) gm PIN FB 5.5V COMP VOSC 1.4V SET OSC S GATE R SLOPE COMP GATE DRIVER PWM COMPARATOR CS + + IN UVLO SDSN n 100kΩ PGND 5.5V GND ADP1621 Figure 3. ADP1621 Simplified Block Diagram Rev.
PAGE 7
Data Sheet ADP1621 PIN CONFIGURATION AND FUNCTION DESCRIPTIONS SDSN 1 COMP 3 FB 4 FREQ 5 10 IN CS ADP1621 9 TOP VIEW (Not to Scale) 8 PIN 7 GATE 6 PGND 06090-003 GND 2 Figure 4. Pin Configuration Table 4. Pin Function Descriptions Pin No. 1 Mnemonic SDSN 2 3 GND COMP 4 FB 5 FREQ 6 PGND 7 GATE 8 PIN 9 CS 10 IN Description Shutdown and Synchronization Input. Turn the ADP1621 on by driving SDSN high; turn it off by driving SDSN low.
PAGE 8
ADP1621 Data Sheet TYPICAL PERFORMANCE CHARACTERISTICS 100 92 90 91 LOAD = 0.5A 90 EFFICIENCY (%) 70 60 50 0.1 10 1 88 87 TA = 25°C VIN = 3.3V VOUT = 5V 85 LOAD CURRENT (A) 84 100 06090-004 30 0.01 LOAD = 1A 86 TA = 25°C fSW = 220kHz VIN = 3.3V VOUT = 5V 40 89 300 700 500 900 1100 1300 06090-007 EFFICIENCY (%) 80 1500 SWITCHING FREQUENCY (kHz) Figure 5. Efficiency vs. Load Current Figure 8. Efficiency vs.
PAGE 9
Data Sheet ADP1621 45 35 MOSFET QG = 25nC GATE RISE AND FALL TIMES (ns) 35 30 25 20 MOSFET QG = 15nC 10 25 tF 20 15 10 5 MOSFET QG = 7nC 5 0 200 400 600 800 1000 1200 1400 1600 1800 SWITCHING FREQUENCY (kHz) 0 0 15 20 25 30 35 45 50 180 200 40 Figure 14. GATE Rise and Fall Times vs. CGATE 2.60 SDSN = 5V 1600 1500 1400 1300 1200 1100 1000 900 800 700 600 500 400 300 200 100 0 fOSC (kHz) 2.55 2.50 2.40 –50 0 50 100 150 TEMPERATURE (°C) 06090-011 2.
PAGE 10
ADP1621 Data Sheet 250 1.6 VIN = 5V CS = 30V 1.4 SHUTDOWN IN CURRENT (µA) TEMPERATURE (°C) 200 150 100 50 VIN = 5V SDSN = 0V 1.2 1.0 0.8 0.6 0.4 10 60 160 110 CS LEAKAGE (nA) 0 –50 06090-016 0 –40 0 50 150 100 TEMPERATURE (°C) Figure 17. Temperature vs. CS Leakage 06090-019 0.2 Figure 20. Shutdown IN Current vs. Temperature 1.2165 VFB = 1.2113V AT 25°C FB BIAS CURRENT IS MEASURED BY FORCING A CONSTANT 1.2113V OVER THE TEMPERATURE RANGE. 8 VIN = 5V SDSN = 0V 1.2155 1.
PAGE 11
Data Sheet ADP1621 TA = 25°C VIN = 3.3V VOUT = 5V LOAD = 0.3A CCM OPERATION LOAD CURRENT FROM 0.2A TO 1.2A 4 4 CH4 = INDUCTOR CURRENT 1 2 CH2 = DRAIN VOLTAGE OUTPUT, AC-COUPLED CH1 5V CH2 5V CH4 500mAΩ M2µs A CH1 2.9V 06090-022 CH1 = GATE CH1 50mV Figure 23. CCM Switching Waveform TA = 25°C VIN = 3.3V VOUT = 5V fSW = 220kHz SOFT-START = 9.3ms CH4 1AΩ M200µs A CH4 700V 06090-025 TA = 25°C VIN = 3.3V VOUT = 5V 1 Figure 26.
PAGE 12
ADP1621 Data Sheet THEORY OF OPERATION CONTROL LOOP The ADP1621 uses a current-mode architecture to regulate the output voltage. The output voltage is monitored at FB through a resistive voltage divider. The voltage at FB is compared to the internal 1.215 V reference voltage by the internal transconductance error amplifier to create an error current at COMP. A resistorcapacitor compensation impedance connected from COMP to GND converts the error current to an error voltage.
PAGE 13
Data Sheet ADP1621 CURRENT LIMIT The current limit is achieved by the COMP voltage clamp, owing to the current-mode operation of the ADP1621. A detailed explanation of how the current limit is determined can be found in the Current Limit section of the Application Information: Boost Converter section. UNDERVOLTAGE LOCKOUT SETTING THE OSCILLATOR FREQUENCY AND SYNCHRONIZATION FREQUENCY The free-running oscillator frequency, fOSC, is set by a resistor from FREQ to GND.
PAGE 14
ADP1621 Data Sheet APPLICATION INFORMATION: BOOST CONVERTER In this section, an analysis of a boost converter is presented, along with guidelines for component selection. A typical boostconverter application circuit is shown in Figure 1. ADIsimPower DESIGN TOOL SETTING THE OUTPUT VOLTAGE The output voltage is set through a voltage divider from the output voltage to the FB input. The feedback resistor ratio sets the output voltage of the system. The regulation voltage at FB is 1.215 V.
PAGE 15
Data Sheet ADP1621 Assuming the ripple current is 30% of 1/(1 − D) times the maximum load current, a reasonable choice for the inductor value is VIN × D × (1 − D ) L= 0.3 × f SW × I LOAD , MAX (9) From this starting point, modify the inductance to obtain the right balance of size, cost, and output voltage ripple while maintaining the inductor ripple current between 20% and 40% of 1/(1 − D) times the maximum load current.
PAGE 16
ADP1621 Data Sheet The MOSFET power dissipation due to conduction is thus The total power dissipation determines the diode junction temperature, which is given by TJ , DIODE = TA + PDIODE × θ JA 2 (17) where TJ,DIODE is the junction temperature, TA is the ambient temperature, and θJA is the junction-to-ambient thermal resistance of the diode package. The diode junction temperature must not exceed its maximum rating at the given power dissipation level.
PAGE 17
Data Sheet ADP1621 f Z ,RHP = (1 − D )2 × RLOAD 2π × L (25) where fZ,RHP is the RHP zero frequency, and RLOAD is the equivalent load resistance or the output voltage divided by the load current. To stabilize the regulator, ensure that the regulator crossover frequency is less than or equal to one-fifth of the RHP zero frequency and less than or equal to one-fifteenth of the switching frequency.
PAGE 18
ADP1621 Data Sheet which vary from part to part and with temperature. If lossless current sensing is used, consider that the on resistance of a MOSFET typically increases with increasing junction temperature. RDSON, of the external power MOSFET. Otherwise, RCS represents the external current-sense resistor.
PAGE 19
Data Sheet ADP1621 Given the minimum on time of the ADP1621, pulse-skipping modulation is also a requirement to maintain output voltage regulation with light loads. During the short switching periods of pulse-skipping modulation, the MOSFET is turned on for the minimum on time each cycle, storing just enough energy in the inductor to charge the output capacitor.
PAGE 20
ADP1621 Data Sheet LAYOUT CONSIDERATIONS Layout is important for all switching regulators, but is particularly important for regulators with high switching frequencies. To achieve high efficiency, good regulation, and stability, a welldesigned printed circuit board layout is required. A sample PCB layout for the standard boost converter circuit shown in Figure 33 is given in Figure 32. Follow these guidelines when designing printed circuit boards: • Keep the low ESR bypass input capacitor of 0.
PAGE 21
Data Sheet ADP1621 EFFICIENCY CONSIDERATIONS The efficiency, η, of a dc/dc converter is given by η= POUT PIN • × 100% (38) where POUT is the output power, and PIN is the input power to the converter. While switching regulators are ideally lossless converters of power, the nonideal characteristics of regulator components degrade the efficiency of the regulator.
PAGE 22
ADP1621 Data Sheet EXAMPLES OF APPLICATION CIRCUITS The next step is to choose a Schottky diode. The average and rms diode currents are calculated to be 1.0 A and 1.3 A, respectively, using Equations 14 and 15. A Vishay SSA33L Schottky diode meets the current and thermal requirements and is an excellent choice. STANDARD BOOST CONVERTER— DESIGN EXAMPLE The example covered here is for the ADP1621 configured as a standard boost converter, as shown in Figure 33, where lossless current sensing is employed.
PAGE 23
Data Sheet ADP1621 BOOTSTRAPPED BOOST CONVERTER The inputs of the ADP1621 can be driven from the step-up converter output voltage to improve efficiency for low input voltages. For low input voltages, bootstrapped operation improves efficiency with heavy loads by increasing the available gate drive voltage, thus reducing the on resistance of the MOSFET.
PAGE 24
ADP1621 Data Sheet VIN = 3.3V D2 C3 1µF 10V R3 700Ω L1 10µH IN PIN CS R1 88.7kΩ 1% RS 200Ω ADP1621 SDSN C2 220pF CCOMP 330pF COUT1 10µF 16V ×2 COUT2 330µF 25V ×2 R2 10kΩ 1% M1 GATE COMP RCOMP 51.5kΩ VOUT = 12V 1A D1 C4 0.1µF 10V PGND FREQ FB GND C1 47µF 6.3V RFREQ 31.6kΩ 1% AGND fOSC = 600kHz C1 = MURATA GRM31CR60J476M COUT2 = RUBYCON 25ZL330M8x16 L1 = COILCRAFT MSS1260-103ML 06090-033 M1 = IRF7470 D1 = VISHAY SSC53L D2 = SIGNAL DIODE Figure 34.
PAGE 25
Data Sheet ADP1621 Low Input and High Output Boost Converter with a single resistor, as shown in Figure 38. When there is a wide input voltage range, it is sometimes desirable to use the pass NPN transistor, as shown in Figure 37. If the input voltage range is narrow, a single resistor connecting to the IN and PIN pins is sufficient, as shown in Figure 38. In Figure 37, Resistor R3 limits the current going into IN, and there is power loss in this resistor.
PAGE 26
ADP1621 Data Sheet VIN = 12V R3 649Ω C3 1µF 10V L1 15µH R1 324kΩ 1% PIN IN FB ADP1621 SDSN C2 120pF CCOMP 18pF FREQ M1 GATE COMP RCOMP 2MΩ VOUT = 40V 1A D1 C4 0.1µF 10V CS PGND GND RS 442Ω COUT1 1µF 100V COUT2 4.7µF 50V COUT3 220µF 63V ×2 R2 10.2kΩ 1% RCS 0.01Ω C1 22µF 16V ×2 RFREQ 34.8Ω AGND fOSC = 560kHz M1 = VISHAY Si7478DP D1 = MBRB7H50 L1 = COILCRAFT MSS1278-153ML Figure 38. High Input Voltage and High Output Voltage Converter Rev.
PAGE 27
Data Sheet ADP1621 SEPIC CONVERTER CIRCUIT load current during this time. When the MOSFET turns off and the diode turns on, the energy in L1 and L2 is released to charge the output capacitor, COUT, and the coupling capacitor, C5, as well as to supply current to the load. A single-ended primary inductance converter (SEPIC) topology is shown in Figure 39. This topology is useful for an unregulated input voltage, where the regulated output voltage falls within the input voltage range.
PAGE 28
ADP1621 Data Sheet LED DRIVER APPLICATION CIRCUITS The ADP1621 can be used as an LED driver. Two LED application circuits are shown in Figure 41 and Figure 42, where each circuit is driving 20 white LEDs in series. Each white LED has a typical current of 150 mA at a typical forward voltage of 4.0 V, with a maximum voltage of 4.5 V over the temperature range of −40°C to +125°C. Two methods for dimming the brightness of the LEDs are shown in Figure 41 and Figure 42.
PAGE 29
Data Sheet ADP1621 VIN = 10V TO 16V RB 800Ω L1 33µH D1 100V C4 0.1µF C3 0.1µF IN PIN M1 100V GATE SDSN CS COMP RCOMP 101kΩ C2 18pF CCOMP 390nF FREQ COUT 1µF 100V ×3 150mA ADP1621 PWM VOUT RS 800Ω 20 LEDS FB PGND GND RCS 3mΩ RFREQ 50kΩ 1% R1 8Ω 1/4W C1 2.2µF 25V AGND C1 = MURATA GRM31MR71E225K COUT = MURATA GRM31CR72A105K L1 = COILCRAFT MSS1038-333NL M1 = VISHAY Si4482DY D1 = IRF 10MQ100 06090-040 fOSC = 400kHz Figure 41.
PAGE 30
ADP1621 Data Sheet RELATED PARTS Table 6. Part Number ADP1612 ADP1613 ADP1614 Description Current-mode PWM step-up controller Current-mode PWM step-up controller Current-mode PWM step-up controller Comments 1.4 A, internal FET RDSON is 130 m Ω nominal, VIN = 1.8 V to 5.5 V, VOUTMAX is 20 V 2.0 A, internal FET RDSON is 130 m Ω nominal, VIN = 2.5 V to 5.5 V, VOUTMAX is 20 V 4.0 A, internal FET RDSON is 50 m Ω nominal, VIN = 2.5 V to 5.5 V, VOUTMAX is 20 V Rev.
PAGE 31
Data Sheet ADP1621 OUTLINE DIMENSIONS 3.10 3.00 2.90 10 3.10 3.00 2.90 1 5.15 4.90 4.65 6 5 PIN 1 IDENTIFIER 0.50 BSC 0.95 0.85 0.75 15° MAX 1.10 MAX 0.30 0.15 6° 0° 0.23 0.13 0.70 0.55 0.40 COMPLIANT TO JEDEC STANDARDS MO-187-BA 091709-A 0.15 0.05 COPLANARITY 0.10 Figure 43.