MAX797HESE+T

19-1239; Rev 0; 7/97 High-Voltage, Step-Down Controller with Synchronous Rectifier for CPU Power The MAX797H comes in a 16-pin narrow SO package. ________________________Applications Notebook and Subnotebook Computers ____________________________Features ♦ 96% Efficiency ♦ Up to 40V Power Input ♦ 2.5V to 6V Adjustable Output ♦ ♦ ♦ ♦ Preset 3.3V and 5V Outputs (at up to 10A) 5V Linear-Regulator Output Precision 2.505V Reference Output Automatic Bootstrap Circuit ♦ ♦ ♦ ♦ 150kHz/300kHz Fixed-Frequency PWM Operation Programmable Soft-Start 375µA Quiescent Current (VIN = 12V, VOUT = 5V) 1µA Shutdown Current ______________Ordering Information PART† MAX797HESE PIN-PACKAGE -40°C to +85°C 16 Narrow SO †U __________Typical Operating Circuit +4V TO +40V POWER INPUT +4.5V TO +30V SUPPLY INPUT Industrial Controls V+ __________________Pin Configuration TEMP. RANGE VL SHDN DH MAX797H BST TOP VIEW SS 1 16 DH SKIP 2 15 LX REF 3 14 BST GND 4 MAX797H LX REF DL 13 DL SYNC 5 12 PGND SHDN 6 11 VL FB 7 10 V+ CSH 8 SS +3.3V OUTPUT 9 CSL PGND SYNC CSH GND CSL SKIP FB SO Idle Mode is a trademark of Maxim Integrated Products. ________________________________________________________________ Maxim Integrated Products 1 For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800 For small orders, phone 408-737-7600 ext. 3468. MAX797H _______________General Description The MAX797H high-performance, step-down DC-DC converter provides main CPU power in battery-powered systems. A 40V rating on the power stage’s input allows operation with high-cell-count batteries and a wide range of AC adaptors. This buck controller achieves 96% efficiency by using synchronous rectification and Maxim’s proprietary Idle Mode™ control scheme to extend battery life at full-load (up to 10A) and no-load outputs. Excellent dynamic response corrects output transients caused by the latest dynamic-clock CPUs within five 300kHz clock cycles. Unique bootstrap circuitry drives inexpensive N -channel MOSFETs, reducing system cost and eliminating the crowbar switching currents found in some PMOS/NMOS switch designs. The MAX797H has a logic-controlled and synchronizable fixed-frequency, pulse-width-modulating (PWM) operating mode, which reduces noise and RF interference in sensi tive mobile-communications and pen-entry applications. The SKIP override input allows automatic switchover to idle-mode operation (for high-efficiency pulse skipping) at light loads, or forces fixed-frequency mode for lowest noise at all loads. The MAX797H is pin compatible with the popular MAX797, but has a higher input voltage range. MAX797H High-Voltage, Step-Down Controller with Synchronous Rectifier for CPU Power ABSOLUTE MAXIMUM RATINGS V+ to GND ................................................................-0.3V to 36V GND to PGND........................................................................±2V VL to GND...................................................................-0.3V to 7V BST to GND ..............................................................-0.3V to 46V DH to LX .....................................................-0.3V to (BST + 0.3V) LX to BST ....................................................................-7V to 0.3V SHDN to GND ...........................................................-0.3V to 36V SYNC, SS, REF, FB, SKIP, DL to GND ...........-0.3V to (VL + 0.3V) CSH, CSL to GND.......................................................-0.3V to 7V VL Short Circuit to GND..............................................Momentary REF Short Circuit to GND ...........................................Continuous VL Output Current ...............................................................50mA Continuous Power Dissipation (TA = +70°C) SO (derate 8.70mW/°C above +70°C) ........................696mW Operating Temperature Range MAX797HESE .................................................-40°C to +85°C Storage Temperature Range .............................-65°C to +160°C Lead Temperature (soldering, 10sec) .............................+300°C Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress rating s only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specificatio ns is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. ELECTRICAL CHARACTERISTICS (V+ = 15V, GND = PGND = 0V, IVL = IREF = 0A, TA = 0°C to +85°C, SYNC = 0V, unless otherwise noted.) PARAMETER CONDITIONS MIN TYP MAX UNITS +3.3V AND +5V STEP-DOWN CONTROLLERS Input Supply Range V+ 4.5 30 High-side MOSFET drain 40 V 5V Output Voltage (CSL) 0mV < (CSH - CSL) < 80mV, FB = VL, 6V < power input < 40V, includes line and load regulation (Note 4) 4.85 5.10 5.25 V 3.3V Output Voltage (CSL) 0mV < (CSH - CSL) < 80mV, FB = 0V, 4.5V < power input < 40V, includes line and load regulation (Note 4) 3.20 3.35 3.46 V Nominal Adjustable Output Voltage Range External resistor divider REF 6 V Feedback Voltage CSH - CSL = 0V 2.43 2.57 V Load Regulation Line Regulation 2.505 0mV < (CSH - CSL) < 80mV 2.5 25mV < (CSH - CSL) < 80mV 1.5 FB = VL, 6V < power input < 40V (Note 4) 0.04 0.06 FB = 0V, 4.5V < power input < 40V (Note 4) 0.04 0.06 % CSH - CSL, positive 80 100 120 CSH - CSL, negative -50 -100 -160 SS Source Current 2.5 4.0 6.5 SS Fault Sink Current 2.0 Current-Limit Voltage %/V mV µA mA FLYBACK/PWM INTERNAL REGULATOR CONTROLLER AND REFERENCE VL Output Voltage SHDN = 2V, 0mA < IVL < 25mA, 5.5V < V+ < 30V 4.7 5.3 V VL Fault Lockout Voltage Rising edge, hysteresis = 15mV 3.8 4.1 V VL/CSL Switchover Voltage Rising edge, hysteresis = 25mV 4.2 4.7 V 2 _______________________________________________________________________________________ High-Voltage, Step-Down Controller with Synchronous Rectifier for CPU Power (V+ = 15V, GND = PGND = 0V, IVL = IREF = 0A, TA = 0°C to +85°C, SYNC = 0V, unless otherwise noted.) MIN TYP MAX UNITS Reference Output Voltage PARAMETER No external load (Note 1) CONDITIONS 2.45 2.505 2.55 V Reference Fault Lockout Voltage Falling edge 1.8 Reference Load Regulation 0µA < IREF < 100µA CSL Shutdown Leakage Current SHDN = 0V, CSL = 6V, V+ = 0V or 30V, VL = 0V V+ Shutdown Current V+ Off-State Leakage Current 2.3 V 50 mV 0.1 1 µA SHDN = 0V, V+ = 30V, CSL = 0V or 6V 1 5 µA FB = CSH = CSL = 6V, VL switched over to CSL 1 5 µA Dropout Power Consumption V+ = 4V, CSL = 0V (Note 2) 4 8 mW Quiescent Power Consumption CSH = CSL = 6V 4.8 6.6 mW OSCILLATOR AND INPUTS/OUTPUTS Oscillator Frequency SYNC = REF 270 300 330 SYNC = 0V or 5V 125 150 175 kHz SYNC High Pulse Width 200 ns SYNC Low Pulse Width 200 ns SYNC Rise/Fall Time Guaranteed by design Oscillator Sync Range Maximum Duty Factor 190 SYNC = REF 89 91 SYNC = 0V or 5V 93 96 SYNC Input High Voltage SHDN, SKIP Input Low Voltage Input Current 200 ns 340 kHz % VL - 0.5 V 2.0 SYNC 0.8 SHDN, SKIP 0.5 SHDN, 0V or 30V 2.0 SYNC, SKIP 1.0 CSH, CSL, CSH = CSL = 4V, device not shut down 50 FB, FB = REF ±100 V µA nA DL Sink/Source Current DL forced to 2V 1 A DH Sink/Source Current DH forced to 2V, BST - LX = 4.5V 1 A DL On-Resistance High or low 7 Ω DH On-Resistance High or low, BST - LX = 4.5V 7 Ω _______________________________________________________________________________________ 3 MAX797H ELECTRICAL CHARACTERISTICS (continued) MAX797H High-Voltage, Step-Down Controller with Synchronous Rectifier for CPU Power ELECTRICAL CHARACTERISTICS (continued) (V+ = 15V, GND = PGND = 0V, IVL = IREF = 0A, TA = -40 to +85°C, SYNC = 0V, unless otherwise noted.) (Note 3) PARAMETER CONDITIONS MIN TYP MAX UNITS +3.3V and +5V STEP-DOWN CONTROLLERS Input Supply Range V+ 5.0 30 High-side MOSFET drain 40 V 5V Output Voltage (CSL) 0mV < (CSH - CSL) < 80mV, FB = VL, 6V < power input < 40V, includes line and load regulation (Note 4) 4.70 5.10 5.40 V 3.3V Output Voltage (CSL) 0mV < (CSH - CSL) < 80mV, FB = 0V, 4.5V < power input < 40V, includes line and load regulation (Note 4) 3.10 3.35 3.56 V Nominal Adjustable Output Voltage Range External resistor divider REF 6.0 V Feedback Voltage CSH - CSL = 0V 2.40 Line Regulation Current-Limit Voltage FB = VL, 6V < power input < 40V (Note 4) FB = 0V, 4.5V < power input < 40V (Note 4) CSH - CSL, positive 70 CSH - CSL, negative -40 2.60 V 0.04 0.06 0.04 0.06 %/V %/V -100 -160 130 mV FLYBACK/PWM INTERNAL REGULATOR CONTROLLER AND REFERENCE VL Output Voltage SHDN = 2V, 0mA < IVL < 25mA, 5.5V < V+ < 30V 4.7 5.3 V VL Fault Lockout Voltage Rising edge, hysteresis = 15mV 3.75 4.15 V VL/CSL Switchover Voltage Rising edge, hysteresis = 25mV 4.2 4.7 V Reference Output Voltage No external load (Note 1) 2.43 Reference Load Regulation 0µA < IREF < 100µA V+ Shutdown Current SHDN = 0V, V+ = 30V, CSL = 0V or 6V V+ Off-State Leakage Current FB = CSH = CSL = 6V, VL switched over to CSL Quiescent Power Consumption CSH = CSL = 6V 2.505 2.57 V 50 mV 1 10 µA 1 10 µA 4.8 8.4 mW OSCILLATOR AND INPUTS/OUTPUTS Oscillator Frequency SYNC = REF 250 300 350 SYNC = 0V or 5V 120 150 180 kHz SYNC High Pulse Width 250 ns SYNC Low Pulse Width 250 ns Oscillator Sync Range Maximum Duty Factor 210 320 SYNC = REF 89 91 SYNC = 0V or 5V 93 96 kHz % DL On-Resistance High or low 7 Ω DH On-Resistance High or low, BST - LX = 4.5V 7 Ω Note 1: Since the reference uses VL as its supply, V+ line-regulation error is insignificant. Note 2: At very low input voltages, quiescent supply current can increase due to excess PNP base current in the VL linear regulator. This occurs only if V+ falls below the preset VL regulation point (5V nominal). Note 3: All -40°C to +85°C specifications are guaranteed by design. Note 4: The power input is the high-side MOSFET drain. 4 _______________________________________________________________________________________ High-Voltage, Step-Down Controller with Synchronous Rectifier for CPU Power PIN NAME 1 SS 2 SKIP Disables pulse-skipping mode when high. Connect SKIP to GND for normal use. Do not leave unconnected. With SKIP grounded, the device automatically changes from pulse-skipping operation to full PWM operation when the load current exceeds approximately 30% of maximum. 3 REF Reference Voltage Output. Bypass REF to GND with 0.33µF minimum. 4 GND Low-noise Analog Ground and Feedback Reference Point 5 SYNC Oscillator Synchronization and Frequency Select. Tie SYNC to GND or VL for 150kHz operation; tie to REF for 300kHz operation. A high-to-low transition begins a new cycle. Drive SYNC with 0V to 5V logic levels (see Electrical Characteristics for VIH and VIL specifications). SYNC capture range is guaranteed to be 190kHz to 340kHz. 6 SHDN Shutdown Control Input, Active Low. Logic threshold is set at approximately 1V (VTH of an internal N-channel MOSFET). Tie SHDN to V+ for automatic start-up. 7 FB FUNCTION Soft-Start Timing Capacitor Connection. Ramp time to full current limit is approximately 1ms/nF. Feedback Input. Regulates at FB = REF (approximately 2.505V) in adjustable mode. FB is a Dual ModeTM input that also selects the fixed-output voltage settings as follows: • Connect to GND for 3.3V operation. • Connect to VL for 5V operation. • Connect to a resistor divider for adjustable mode. FB can be driven with 5V Rail-to-Rail® logic to change the output voltage under system control. 8 CSH Current-Sense Input, High Side. Current-limit level is 100mV referred to CSL. 9 CSL Current-Sense Input, Low Side. CSL also serves as the feedback input in fixed-output modes. 10 V+ Battery Voltage Input (4.5V to 30V). Bypass V+ to PGND close to the IC with a 0.1µF capacitor. Connects to a linear regulator that powers VL. 11 VL 5V Internal Linear-Regulator Output. VL is also the supply-voltage rail for the chip. It is switched to the output voltage via CSL (VCSL > 4.5V) for automatic bootstrapping. Bypass to GND with 4.7µF. VL can supply up to 5mA for external loads. 12 PGND 13 DL Low-Side Gate-Drive Output. DL normally drives the synchronous-rectifier MOSFET. Swings 0V to VL. 14 BST Boost Capacitor Connection for High-Side Gate Drive (0.1µF) 15 LX Switching Node (inductor) Connection. LX can swing 2V below ground without hazard. 16 DH High-Side Gate-Drive Output. DH normally drives the main buck switch. It is a floating driver output that swings from LX to BST, riding on the LX switching-node voltage. Power Ground Dual Mode is a trademark of Maxim Integrated Products. Rail-to-Rail is a registered trademark of Nippon Motorola Ltd. _______________________________________________________________________________________ 5 MAX797H ______________________________________________________________Pin Description MAX797H High-Voltage, Step-Down Controller with Synchronous Rectifier for CPU Power _______________Detailed Description The MAX797H is functionally identical to the MAX797. The only difference between the two devices is in the BST pin’s absolute maximum rating. The MAX797H’s rating is 46V; the MAX797’s rating is 36V. The higher rating allows the MAX797H to use a power input up to 40V, provided that the V+ pin is powered by a separate supply between 4.5V and 30V. Circuit design and component selection for the MAX797H are identical to those for the MAX797; there fore, such information is not included in this data sheet. Refer to the MAX796/MAX797/MAX799 data sheet for design formulas and applications information. The Applications Information section in this data sheet con tains suggestions for providing the 30V maximum V+ supply input for the MAX797H when power input exceeds 30V. __________Applications Information Powering the V+ Pin V+ can be supplied directly if a system supply between 4.5V and 30V is available (see the Typical Operating Circuit). Most of the MAX797H’s internal blocks are sup plied by VL, which uses V+ as its input. While the cur rent into V+ is minimal, it depends heavily on the type of external MOSFET used and the switching frequency: IGATE = Qg x fSW where Q g is the sum of the high- and low-side MOSFET’s total gate charges, and f SW is the switching frequency. Furthermore, if the circuit output voltage on CSL exceeds the VL/CSL switchover voltage, the MAX797H bootstraps itself (it connects VL to CSL and turns off the linear regulator, supplying the IC from the circuit output), and V+ current is reduced to about 1µA. If a 5V regulated supply is available, V+ and VL can be connected and fed from that supply (Figure 1). In this mode, the VL regulator is bypassed. Do not use this approach if the output voltage on CSL can exceed the VL/CSL switchover voltage. If a 5V regulated supply is not available, a linear regula tor with a sufficient input voltage range can provide it (Figure 2). This approach allows for a very wide input voltage range, which is useful if the circuit must run from several different power sources. The drawback of the linear regulator is the high quiescent current that these devices typically require, in addition to the current used by the feedback divider resistors (R1 and R2). 6 For most applications, a better choice than Figure 2’s circuit takes advantage of the MAX797H’s internal lin ear regulator. There is no need to provide a regulated supply to V+, provided it is within the +4.5V to +30V V+ input voltage range. In Figure 3, Q1 is used to drop a 40V (max) input to 30V by dividing it by approximately 4/3. This approach results in a somewhat higher mini mum input voltage than that of Figure 2’s circuit, but a much lower quiescent current than that of a linear regu lator. If quiescent current must be minimized, an N-channel MOSFET can be substituted for Q1, and the divider-resistor values can be increased. Powering V+ with a zener diode can be done in many different ways. The simplest is to use a standard shunt regulator to provide a regulated voltage in the 4.5V to 30V range (Figure 4). Resistor R1 must be chosen to allow the maximum required V+ current to be obtained from the minimum power input voltage. If the power input voltage varies appreciably, the result is higherthan-necessary input current from the highest power input voltage. An approach that reduces quiescent current is to use a zener diode as a dropping diode to keep V+ under 30V (Figure 5). This results in a severely restricted minimum range for the power input voltage, which is not a problem for most high-voltage applica tions. RL must be added to draw current and to ensure that there is sufficient forward drop across the zener diode if the MAX797H can be shut down or bootstrap off its output voltage. Duty-Factor Limitations for Low VOUT/VIN Ratios The MAX797H’s output voltage is adjustable down to 2.5V (min). However, the combination of high input and low output voltages may not be possible at high switch ing frequencies without introducing some amount of frequency instability. The minimum duty factor is deter mined by delays through the error comparator, internal logic, gate drivers, and external MOSFETs. The delay is typically 425ns. With a switching period of 3.33 µs (300kHz), the minimum duty factor is 0.425 µs / 3.33 µs = 0.13. If V OUT / V IN is less than this value, the IC will properly regulate the output voltage, but may extend the period and switch at 150kHz instead of 300kHz. It may also alternate between these two frequencies. For example, if V IN is 40V, the lowest V OUT that does not require less than the minimum duty factor is 40V x 0.13 = 5.2V. Below this output voltage, select the 150kHz switching frequency (connect SYNC to VL or GND). _______________________________________________________________________________________ High-Voltage, Step-Down Controller with Synchronous Rectifier for CPU Power V+ MAX797H +5V REGULATED SUPPLY +4V TO +40V POWER INPUT VL SHDN MAX797H DH BST SS LX REF DL +3.3V OUTPUT PGND CSH SYNC GND SKIP CSL FB Figure 1. Powering V+ and VL from a Regulated +5V supply Similarly, at 150kHz, the minimum duty factor is 0.425µs / 6.67µs = 0.064. This means that duty factor is not an issue except at the maximum input voltage and minimum output voltage. For example, if V IN is 40V, the lowest V OUT that does not require less than the minimum duty factor is 40V x 0.064 = 2.56V. If V OUT / VIN is less than this value, the IC will properly regulate the output voltage, but may extend the period and switch at 75kHz instead of 150kHz. It may also alter nate between these two frequencies. _______________________________________________________________________________________ 7 MAX797H High-Voltage, Step-Down Controller with Synchronous Rectifier for CPU Power OUT +8V TO +40V POWER INPUT IN ADJ 100k R1 +7V TO +40V INPUT Q1 300k R2 V+ V+ VL VL SHDN SHDN MAX797H MAX797H DH Figure 2. Powering V+ and VL with a +5V Linear Regulator DH Figure 3. Dividing the Power Input to Supply V+ +20V TO +40V POWER INPUT UP TO +40V POWER INPUT 12V R1 R1 V+ V+ VL VL SHDN SHDN MAX797H MAX797H DH Figure 4. Powering V+ with a Zener Shunt Regulator DH Figure 5. Powering V+ with a Zener Dropping Diode ___________________Chip Information TRANSISTOR COUNT: 913 Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. N o circu implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. it patent licenses are 8 ___________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600 © 1997 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.