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General Description

The MAX1652–MAX1655 are high-efficiency, pulse-

width-modulated (PWM), step-down DC-DC controllers

in small QSOP packages. The MAX1653/MAX1655 also

come in 16-pin narrow SO packages that are pin-

compatible upgrades to the popular MAX797. Improve-

ments include higher duty-cycle operation for better

dropout, lower quiescent supply currents for better

light-load efficiency, and an output voltage down to 1V

(MAX1655).

The MAX1652–MAX1655 achieve up to 96% efficiency

and deliver up to 10A using a unique Idle Mode™ syn-

chronous-rectified PWM control scheme. These devices

automatically switch between PWM operation at heavy

loads and pulse-frequency-modulated (PFM) operation

at light loads to optimize efficiency over the entire out-

put current range. The MAX1653/MAX1655 also feature

logic-controlled, forced PWM operation for noise-sensi-

tive applications.

All devices operate with a selectable 150kHz/300kHz

switching frequency, which can also be synchronized

to an external clock signal. Both external power switch-

es are inexpensive N-channel MOSFETs, which provide

low resistance while saving space and reducing cost.

The MAX1652 and MAX1654 have an additional feed-

back pin that permits regulation of a low-cost second

output tapped from a transformer winding. The

MAX1652 provides an additional positive output. The

MAX1654 provides an additional negative output.

The MAX1652–MAX1655 have a 4.5V to 30V input volt-

age range. The MAX1652/MAX1653/MAX1654’s output

range is 2.5V to 5.5V while the MAX1655’s output range

extends down to 1V. An evaluation kit (MAX1653EVKIT)

is available to speed designs.

Applications

Notebook Computers

PDAs

Cellular Phones

Hand-Held Computers

Handy-Terminals

Mobile Communicators

Distributed Power

____________________________Features

♦ 96% Efficiency

♦ Small, 16-Pin QSOP Package

(half the size of a 16-pin narrow SO)

♦ Pin-Compatible with MAX797 (MAX1653/MAX1655)

♦ Output Voltage Down to 1V (MAX1655)

♦ 4.5V to 30V Input Range

♦ 99% Duty Cycle for Lower Dropout

♦ 170µA Quiescent Supply Current

♦ 3µA Logic-Controlled Shutdown

♦ Dual, N-Channel, Synchronous-Rectified Control

♦ Fixed 150kHz/300kHz PWM Switching,

or Synchronized from 190kHz to 340kHz

♦ Programmable Soft Start

♦ Low-Cost Secondary Outputs (MAX1652/MAX1654)

MAX1652–MAX1655

High-Efficiency, PWM, Step-Down

DC-DC Controllers in 16-Pin QSOP

________________________________________________________________

Maxim Integrated Products

19-1357; Rev 1; 7/98

EVALUATION KIT

AVAILABLE

Ordering Information

Selection Guide

Pin Configurations appear at end of data sheet.

Idle Mode is a trademark of Maxim Integrated Products.

PART

FEEDBACK

VOLTAGE (V)

SPECIAL

FEATURE

COMPATIBILITY

MAX1652 2.5

Regulates positive

secondary voltage

(such as +12V)

Same pin order

as MAX796, but

smaller package

MAX1653 2.5

Logic-controlled,

low-noise mode

Pin-compatible

with MAX797

MAX1654 2.5

Regulates negative

secondary voltage

(such as -5V)

Same pin order

as MAX799, but

smaller package

MAX1655 1

Low output volt-

ages (1V to 5.5V);

logic-controlled,

low-noise mode

Pin compatible

with MAX797

(except for feed-

back voltage)

PART

MAX1652EEE

-40°C to +85°C

TEMP. RANGE PIN-PACKAGE

16 QSOP

MAX1653EEE -40°C to +85°C 16 QSOP

MAX1654EEE

-40°C to +85°C 16 QSOP

MAX1653ESE

-40°C to +85°C 16 Narrow SO

MAX1655ESE

-40°C to +85°C 16 Narrow SO

MAX1655EEE -40°C to +85°C 16 QSOP

Summary of content (28 pages)

PAGE 1
9-1357; Rev 1; 7/98 KIT ATION EVALU E L B AVAILA High-Efficiency, PWM, Step-Down DC-DC Controllers in 16-Pin QSOP ____________________________Features ♦ 96% Efficiency The MAX1652–MAX1655 achieve up to 96% efficiency and deliver up to 10A using a unique Idle Mode™ synchronous-rectified PWM control scheme. These devices automatically switch between PWM operation at heavy loads and pulse-frequency-modulated (PFM) operation at light loads to optimize efficiency over the entire output current range.
PAGE 2
MAX1652–MAX1655 High-Efficiency, PWM, Step-Down DC-DC Controllers in 16-Pin QSOP ABSOLUTE MAXIMUM RATINGS V+ to GND ..............................................................-0.3V to +36V GND to PGND .......................................................-0.3V to +0.3V VL to GND ................................................................-0.3V to +6V BST to GND ............................................................-0.3V to +36V DH to LX .....................................................-0.
PAGE 3
High-Efficiency, PWM, Step-Down DC-DC Controllers in 16-Pin QSOP (V+ = +15V, GND = PGND = 0V, SYNC = REF, IVL = IREF = 0A, TA = 0°C to +85°C, unless otherwise noted.) MIN TYP MAX UNITS Reference Output Voltage PARAMETER No external load (Note 1) CONDITIONS 2.46 2.50 2.54 V Reference Fault Lockout Voltage Falling edge 2.0 Reference Load Regulation 0 < IREF < 100µA CSL, CSH Shutdown Leakage Current SHDN = 0V, CSL = 5.5V, CSH = 5.
PAGE 4
MAX1652–MAX1655 High-Efficiency, PWM, Step-Down DC-DC Controllers in 16-Pin QSOP ELECTRICAL CHARACTERISTICS (continued) (V+ = +15V, GND = PGND = 0V, SYNC = REF, IVL = IREF = 0A, TA = -40°C to +85°C, unless otherwise noted.) (Note 3) PARAMETER CONDITIONS MIN TYP MAX UNITS 4.5 30 V 3.3V and 5V STEP-DOWN CONTROLLERS Input Supply Range 5V Output Voltage (CSL) 0 < (CSH - CSL) < 70mV, FB = VL, 6V < V+ < 30V, includes line and load regulation 4.80 5.30 V 3.
PAGE 5
High-Efficiency, PWM, Step-Down DC-DC Controllers in 16-Pin QSOP INPUT 4.5V TO 30V V+ VL SHDN MAX1653 MAX1655 DH BST SS LX REF DL +3.
PAGE 6
High-Efficiency, PWM, Step-Down DC-DC Controllers in 16-Pin QSOP MAX1652–MAX1655 Typical Operating Circuits (continued) INPUT 6V TO 30V FROM REF V+ SECFB SHDN FB VL MAX1654 -5V OUTPUT DH BST +5V OUTPUT LX DL SS PGND REF CSH GND CSL SYNC __________________________________________Typical Operating Characteristics (Circuit of Figure 1, SKIP = GND, TA = +25°C, unless otherwise noted.) EFFICIENCY vs. LOAD CURRENT (3.
PAGE 7
High-Efficiency, PWM, Step-Down DC-DC Controllers in 16-Pin QSOP V+ = 28V 70 0.01 V+ = 28V V+ = 12V 70 0.1 1 V+ = 24V V+ = 12V 50 0.001 0.01 0.1 1 50 0.001 10 0.01 0.1 1 10 LOAD CURRENT (A) LOAD CURRENT (A) IDLE-MODE SUPPLY CURRENT vs. INPUT VOLTAGE (3.3V/3A CIRCUIT) PWM-MODE SUPPLY CURRENT vs. INPUT VOLTAGE (3.3V/3A CIRCUIT) SHUTDOWN SUPPLY CURRENT vs. INPUT VOLTAGE 20 15 10 8 5 10 15 20 25 4 0 0 30 6 2 0 0.
PAGE 8
Typical Operating Characteristics (continued) (Circuit of Figure 1, SKIP = GND, TA = +25°C, unless otherwise noted.) DROPOUT VOLTAGE vs. LOAD CURRENT (3.3V/3A CIRCUIT) MAX1652 toc09 500 OUTPUT SET FOR 5V (FB = VL) VOUT > 4.85V DROPOUT VOLTAGE (mV) MAX1652–MAX1655 High-Efficiency, PWM, Step-Down DC-DC Controllers in 16-Pin QSOP 400 300 f = 300kHz 200 100 f = 150kHz 0 0.01 0.
PAGE 9
High-Efficiency, PWM, Step-Down DC-DC Controllers in 16-Pin QSOP PIN NAME 1 SS FUNCTION Soft-Start Timing Capacitor Connection. Ramp time to full current limit is approximately 1ms/nF. SECFB (MAX1652/ MAX1654) Secondary Winding Feedback Input. Normally connected to a resistor divider from an auxiliary output. Don’t leave SECFB unconnected. • MAX1652: SECFB regulates at VSECFB = 2.50V. Tie to VL if not used. • MAX1654: SECFB regulates at VSECFB = 0V.
PAGE 10
MAX1652–MAX1655 High-Efficiency, PWM, Step-Down DC-DC Controllers in 16-Pin QSOP Standard Application Circuits Detailed Description It’s easy to adapt the basic MAX1653 single-output 3.3V buck converter (Figure 1) to meet a wide range of applications with inputs up to 30V (limited by choice of external MOSFET). Simply substitute the appropriate components from Table 1 (candidate suppliers are provided in Table 2).
PAGE 11
High-Efficiency, PWM, Step-Down DC-DC Controllers in 16-Pin QSOP COMPONENT 3.3V at 1A 3.3V at 2A 5V/3.3V at 3A 3.3V at 5A 1.8V at 2.5A Input Range 4.75V to 28V 4.75V to 28V 4.75V to 28V 4.75V to 28V 4.
PAGE 12
MAX1652–MAX1655 High-Efficiency, PWM, Step-Down DC-DC Controllers in 16-Pin QSOP The MAX1652–MAX1655 contain nine major circuit blocks, which are shown in Figure 2: PWM Controller Blocks: • Multi-Input PWM Comparator • Current-Sense Circuit • PWM Logic Block • Dual-Mode Internal Feedback Mux • Gate-Driver Outputs • Secondary Feedback Comparator Bias Generator Blocks: • +5V Linear Regulator • Automatic Bootstrap Switchover Circuit • +2.
PAGE 13
High-Efficiency, PWM, Step-Down DC-DC Controllers in 16-Pin QSOP MAX1652–MAX1655 BATTERY VOLTAGE TO CSL V+ +5V LINEAR REGULATOR 4.5V OUT VL +5V AT 5mA AUXILIARY OUTPUT SHDN BST SECFB DH PWM LOGIC LX MAIN OUTPUT DL +2.50V REF +2.50V AT 100µA PGND PWM COMPARATOR CSH REF CSL LPF 12kHz GND ON/OFF 3.3V FB 5V FB SHDN SS ADJ FB FB MAX1652 MAX1653 MAX1654 MAX1655 4V SYNC 1V Figure 2.
PAGE 14
MAX1652–MAX1655 High-Efficiency, PWM, Step-Down DC-DC Controllers in 16-Pin QSOP CSH CSL 2.5V (1V, MAX1655) FROM FEEDBACK DIVIDER MAIN PWM COMPARATOR BST R LEVEL SHIFT Q S DH LX SLOPE COMP OSC IDLE MODE COMPARATOR SKIP (MAX1653/ MAX1655 ONLY) 25mV VL 4µA CURRENT LIMIT SHOOTTHROUGH CONTROL 24R SS 2.
PAGE 15
High-Efficiency, PWM, Step-Down DC-DC Controllers in 16-Pin QSOP MAX1652–MAX1655 VL R1 R2 TO PWM LOGIC UNCOMPENSATED HIGH-SPEED LEVEL TRANSLATOR AND BUFFER OUTPUT DRIVER FB I1 I2 I3 REF CSH CSL SLOPE COMPENSATION Figure 4. Main PWM Comparator Block Diagram In discontinuous (light-load) mode, the synchronous switch is turned off as the inductor current falls through zero. The synchronous rectifier works under all operating conditions, including idle mode.
PAGE 16
MAX1652–MAX1655 High-Efficiency, PWM, Step-Down DC-DC Controllers in 16-Pin QSOP BATTERY +5V VL SUPPLY INPUT VL VL MAX1652 MAX1653 MAX1654 MAX1655 BST DH LEVEL TRANSLATOR PWM LX Oscillator Frequency and Synchronization (SYNC Pin) The SYNC input controls the oscillator frequency. Connecting SYNC to GND or to VL selects 150kHz operation; connecting SYNC to REF selects 300kHz. SYNC can also be used to synchronize with an external 5V CMOS clock generator.
PAGE 17
High-Efficiency, PWM, Step-Down DC-DC Controllers in 16-Pin QSOP SHDN SKIP LOAD CURRENT MODE NAME Low X X Shutdown DESCRIPTION All circuit blocks turned off; supply current = 3µA typ High Low Low, <10% Idle Pulse-skipping; supply current = 300µA typ at VIN = 10V; discontinuous inductor current High Low Medium, <30% Idle Pulse-skipping; continuous inductor current High Low High, >30% PWM Constant-frequency PWM; continuous inductor current High High X Constant-frequency PWM regardle
PAGE 18
MAX1652–MAX1655 High-Efficiency, PWM, Step-Down DC-DC Controllers in 16-Pin QSOP With high input voltages, the required duty factor is approximately (VOUT + VQ2)/ VIN, where VQ2 is the voltage drop across the synchronous rectifier. The MAX1652’s minimum duty factor is determined by delays through the feedback network, error comparator, internal logic gate drivers, and the external MOSFETs, which typically total 400ns.
PAGE 19
High-Efficiency, PWM, Step-Down DC-DC Controllers in 16-Pin QSOP Shutdown Shutdown mode (SHDN = 0V) reduces the V+ supply current to typically 3µA. In this mode, the reference and VL are inactive. SHDN is a logic-level input, but it can be safely driven to the full V+ range. Connect SHDN to V+ for automatic start-up. Do not allow slow transitions (slower than 0.02V/µs) on SHDN.
PAGE 20
MAX1652–MAX1655 High-Efficiency, PWM, Step-Down DC-DC Controllers in 16-Pin QSOP __________________Design Procedure The predesigned standard application circuits (Figure 1 and Table 1) contain ready-to-use solutions for common applications. Use the following design procedure to optimize the basic schematic for different voltage or current requirements. Before beginning a design, firmly establish the following: VIN(MAX), the maximum input (battery) voltage.
PAGE 21
High-Efficiency, PWM, Step-Down DC-DC Controllers in 16-Pin QSOP IRMS = ILOAD x VOUT (VIN − VOUT) VIN IRMS = ILOAD / 2 when VIN is 2 x VOUT Output Filter Capacitor Value The output filter capacitor values are determined by the ESR, capacitance, and voltage rating requirements. Electrolytic and tantalum capacitors are generally chosen by voltage rating and ESR specifications, as they will generally have more output capacitance than is required for AC stability.
PAGE 22
MAX1652–MAX1655 High-Efficiency, PWM, Step-Down DC-DC Controllers in 16-Pin QSOP Power from the main and secondary outputs is lumped together to obtain an equivalent current referred to the main output voltage (see Inductor Value section for definitions of parameters). Set the value of the currentsense resistor at 80mV / ITOTAL.
PAGE 23
High-Efficiency, PWM, Step-Down DC-DC Controllers in 16-Pin QSOP Rectifier Diode D3 (Transformer Secondary Diode) The secondary diode in coupled-inductor applications must withstand high flyback voltages greater than 60V, which usually rules out most Schottky rectifiers. Common silicon rectifiers such as the 1N4001 are also prohibited, as they are far too slow. This often makes fast silicon rectifiers such as the MURS120 the only choice.
PAGE 24
MAX1652–MAX1655 High-Efficiency, PWM, Step-Down DC-DC Controllers in 16-Pin QSOP __________Applications Information Heavy-Load Efficiency Considerations The major efficiency loss mechanisms under loads (in the usual order of importance) are: • P(I2R), I2R losses • P(gate), gate-charge losses • P(diode), diode-conduction losses • P(tran), transition losses • P(cap), capacitor ESR losses • P(IC), losses due to the operating supply current of the IC Inductor-core losses are fairly low at heavy loads because t
PAGE 25
High-Efficiency, PWM, Step-Down DC-DC Controllers in 16-Pin QSOP 2) Place the IC and signal components. Keep the main switching node (LX node) away from sensitive analog components (current-sense traces and REF and SS capacitors). Placing the IC and analog components on the opposite side of the board from the power-switching node is desirable. Important: the IC must be no farther than 10mm from the currentsense resistor.
PAGE 26
___________________Chip Information TRANSISTOR COUNT: 1990 ________________________________________________________Package Information QSOP.
PAGE 27
High-Efficiency, PWM, Step-Down DC-DC Controllers in 16-Pin QSOP SOICN.
PAGE 28
MAX1652–MAX1655 High-Efficiency, PWM, Step-Down DC-DC Controllers in 16-Pin QSOP NOTES 28 ______________________________________________________________________________________