Datasheet

ManualsBrandsMAXIM INTEGRATED ManualsPMICsPMIC - DC/DC voltage regulator Holder uMAX 10

General Description

The MAX1973/MAX1974 are constant-frequency

1.4MHz pulse-width-modulated (PWM) current-mode

step-down regulators. The output voltage can be set as

low as 0.75V using an external voltage-divider, or it can

be set to preset outputs of 1V, 1.5V (MAX1974), 1.8V,

or 2.5V (MAX1973) without requiring external resistors.

The MAX1973 also includes a voltage-margining fea-

ture that offsets the output voltage up or down 4% to

facilitate board-level production testing.

A fixed 1.4MHz operating frequency ensures operation

outside the DSL frequency band, provides fast transient

response, and allows the use of small external compo-

nents. Only 4.7µF input and output ceramic capacitors

are needed for 1A applications. Forced PWM operation

ensures a constant switching frequency over all load

conditions.

Output voltage accuracy is ±1% over load, line, and

temperature operating ranges. The MAX1973 features

voltage margining; the MAX1974 provides a POK out-

put to indicate when the output has reached 90% of its

nominal regulation voltage. Both devices are available

in small 10-pin µMAX packages.

Applications

Network Equipment

Cellular Base Stations

DSL and Wireless Modems/Routers

Optical Modules

Central-Office DSL and Telecom

DSP/ASIC Core and IO supplies

Features

♦ Tiny Circuit Footprint of 0.19in

♦ Ultra-Low Circuit Height of 1.8mm

♦ 4.7µF Ceramic Input and Output Capacitors

♦ 2.6V to 5.5V Input Voltage

♦ 1A Output Current

♦ 1% Accurate

♦ Built-In ±4% Logic-Controlled Voltage Margining

(MAX1973)

♦ Preset 1V, 1.5V, 1.8V, 2.5V, or 0.75V to V

Adjustable Output

♦ Fixed-Frequency PWM Current-Mode Operation

♦ 1.4MHz Switching Frequency, Operate Outside

DSL Band

♦ 100% Duty-Cycle Dropout Capability

♦ Small External Components

MAX1973/MAX1974

Smallest 1A, 1.4MHz Step-Down Regulators

________________________________________________________________ Maxim Integrated Products 1

CTL1

PGNDSS

COMP

FBSEL

MAX1973

µMAX

TOP VIEW

CTL2GND

PGNDSS

COMP

FBSEL

MAX1974

µMAX

POKGND

Pin Configurations

Ordering Information

MAX1973

COMP

FBSEL

GND

CTL1

CTL2

PGND

INPUT

2.6V TO 5.5V

MAX1974 OUTPUT DOWN TO 0.75V

VOLTAGE

MARGINING

ON/OFF

OUTPUT

1.25V TO V

Typical Operating Circuit

19-2547; Rev 0; 7/02

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.

PART TEMP RANGE PIN-PACKAGE

MAX1973EUB -40°C to +85°C 10 µMAX

MAX1974EUB -40°C to +85°C 10 µMAX

Selector Guide appears at end of data sheet.

Summary of content (15 pages)

PAGE 1
9-2547; Rev 0; 7/02 Smallest 1A, 1.4MHz Step-Down Regulators Features The MAX1973/MAX1974 are constant-frequency 1.4MHz pulse-width-modulated (PWM) current-mode step-down regulators. The output voltage can be set as low as 0.75V using an external voltage-divider, or it can be set to preset outputs of 1V, 1.5V (MAX1974), 1.8V, or 2.5V (MAX1973) without requiring external resistors.
PAGE 2
MAX1973/MAX1974 Smallest 1A, 1.4MHz Step-Down Regulators ABSOLUTE MAXIMUM RATINGS IN, POK, CTL1, CTL2, FBSEL, ON to GND ..............-0.3V to +6V COMP, FB, SS to GND ................................-0.3V to (VIN + 0.3V) PGND to GND .......................................................-0.3V to +0.3V LX Current (Note 1) ...............................................-2.4A to +2.4A Continuous Power Dissipation (TA = +70°C) 10-Pin µMAX (derate 5.6mW/°C above +70°C) ..........
PAGE 3
Smallest 1A, 1.4MHz Step-Down Regulators MAX1973/MAX1974 ELECTRICAL CHARACTERISTICS (continued) (VIN = VCTL_ = 3.3V, FB = OUT, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) MIN TYP MAX UNITS SS Source Current PARAMETER CONDITIONS -25 -20 -15 µA SS Sink Current 10 20 35 µA SS to GND Resistance in Shutdown 5 40 100 Ω FBSEL Low Input Threshold 0.3 V High Input Threshold Input Bias Current FBSEL = GND or IN, VIN = 5.5V VIN 0.
PAGE 4
MAX1973/MAX1974 Smallest 1A, 1.4MHz Step-Down Regulators ELECTRICAL CHARACTERISTICS (continued) (VIN = VCTL_ = 3.3V, FB = OUT, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER CONDITIONS MIN TYP MAX UNITS THERMAL SHUTDOWN Thermal-Shutdown Threshold +170 °C Thermal-Shutdown Hysteresis 20 °C ELECTRICAL CHARACTERISTICS (VIN = VFB = VCTL_ = 3.3V, TA = -40°C to +85°C, unless otherwise noted.) (Note 2) PARAMETER CONDITIONS MIN TYP MAX UNITS 2.6 5.5 V 2.
PAGE 5
Smallest 1A, 1.4MHz Step-Down Regulators MAX1973/MAX1974 ELECTRICAL CHARACTERISTICS (VIN = VCTL_ = 3.3V, FB = OUT, TA = -40°C to +85°C, unless otherwise noted.) (Note 2) PARAMETER CONDITIONS SS to GND Resistance in Shutdown MIN TYP MAX UNITS 5 40 100 Ω FBSEL Low Input Threshold 0.3 V VIN 0.4 V -20 +20 µA Transconductance from FB to COMP 40 80 µS COMP to GND Resistance in Shutdown 5 100 Ω Clamp Voltage Low 0.6 1.2 V Clamp Voltage High 1.3 2.2 V 0.
PAGE 6
Typical Operating Characteristics (Circuits of Figure 2, 3, and 4; TA = +25°C, unless otherwise noted.) EFFICIENCY vs. LOAD CURRENT VOUT = 1.8V 40 70 60 50 40 30 30 20 20 10 0 VIN = 5V 0 0.01 0.1 1 0.1 NO-LOAD CURRENT vs. INPUT VOLTAGE FB VOLTAGE vs. LOAD CURRENT 4 1.250 1.249 1.248 1.247 MAX1973 VIN = 5V R1 = 22kΩ R2 = 13kΩ 1.246 2 1.245 VOUT = 2.5V 0 1 2 3 4 0.2 0.4 0.6 LOAD CURRENT (A) 0.2 0.4 0.6 0.8 1.0 1.0 0.5 VOUT = 1.8V 0 -0.5 2.5V -1.0 1V -1.5 -2.0 -2.5 -3.
PAGE 7
Smallest 1A, 1.4MHz Step-Down Regulators MAX1974 STARTUP WAVEFORMS MAX1973 HIGH-CURRENT SWITCHING WAVEFORMS MAX1973/74 toc08 MAX1973/74 toc09 10V/div 0 2V/div 0 ON POK 20mV/div VOUT VLX 5V/div 1V/div VOUT 0 0 200mA/div 500mA/div IL IIN 0 0 VIN = 5V, 100kΩ PULLUP RESISTOR POK TO VOUT 500ns/div VIN = 5V, VOUT = 2.
PAGE 8
MAX1973/MAX1974 Smallest 1A, 1.4MHz Step-Down Regulators Typical Operating Characteristics (continued) (Circuits of Figure 2, 3, and 4; TA = +25°C, unless otherwise noted.) MAX1974 POK AND INPUT VOLTAGE MAX1973 VOLTAGE MARGIN STEP CHANGE RESPONSE MAX1973/74 toc15 MAX1973/74 toc14 VOUT 1V/div VPOK 2V/div VCTL1 0 10V/div 0 10V/div 0 VCTL2 IIN 500mA/div 0 VOUT 1V/div VIN 0 2V/div 0 1ms/div VIN = 5V, VOUT = 2.
PAGE 9
Smallest 1A, 1.4MHz Step-Down Regulators The MAX1973/MAX1974 are 1.4MHz fixed-frequency PWM current-mode step-down DC/DC converters. A high 1.4MHz switching frequency allows use of small inductors and small capacitors for filtering and decoupling. An internal synchronous rectifier improves efficiency and eliminates the need for an external Schottky freewheeling diode. On-chip current sensing uses the on-resistance of the internal MOSFETs, eliminating current-sensing resistors and improving efficiency.
PAGE 10
MAX1973/MAX1974 Smallest 1A, 1.4MHz Step-Down Regulators MAX1974 ONLY VOLTAGE CLAMP POK COMP OUT IN PMOS CURRENT SENSE FEEDBACK SELECT FB CTL1 VOLTAGE MARGINING MAX1973 ONLY LX ERROR AMP PWM LOGIC BLOCK CTL2 PWM COMPARATOR ON SOFT-START Σ NMOS CURRENT LIMIT MAX1974 ONLY PGND SS REFERENCE GND 1.4MHz OSCILLATOR SLOPE COMP REFERENCE READY MAX1973 MAX1974 CHIP ENABLE BIAS IN UNDERVOLTAGE LOCK OUT Figure 1.
PAGE 11
Smallest 1A, 1.4MHz Step-Down Regulators A shutdown feature is included on both the MAX1973 and the MAX1974. Shutdown turns off the IC and reduces the supply current about 0.1µA. For the MAX1974, drive ON high for normal operation, or low for shutdown. For the MAX1973, drive both CTL1 and CTL2 high for normal operation, or drive both low for shutdown. For a simple enable/shutdown function with no voltage margining on the MAX1973, connect CTL1 to CTL2 and drive as one input.
PAGE 12
MAX1973/MAX1974 Smallest 1A, 1.4MHz Step-Down Regulators 3.3µH VIN = 2.6V TO 5.5V 4.7µF IN LX COMP FB 1.8V 36kΩ 4.7µF VIN = 2.6V TO 5.5V 4.7µF LX COMP FB RC CC 470pF MAX1973 3.3µH IN MAX1973 CTL1 FBSEL SS CTL2 SS CTL2 GND PGND GND PGND FBSEL 1.25V TO VIN R1 4.7µF CTL1 R2 0.1µF 0.1µF Figure 2. MAX1973 with 1.8V Preset Output VIN = 2.6V TO 5.5V 4.7µF Figure 4. MAX1973 with Adjustable Output Voltage Set by R1 and R2 3.3µH IN LX COMP FB 1.5V 43kΩ 330pF IN 4.
PAGE 13
Smallest 1A, 1.4MHz Step-Down Regulators PART INDUCTANCE (µH) ESR (mΩ) SATURATION CURRENT (A) DIMENSIONS L ✕ W ✕ H (mm) Coilcraft LPO1704-32M 3.3 160 1.3 5.5 ✕ 6.6 ✕ 1 Sumida CDRD3D16-R3 3.3 85 1.1 4 ✕ 4 ✕ 1.8 Toko A682AY-3R3M 3.3 134 0.97 4.4 ✕ 4.4 ✕ 3.1 MANUFACTURER response of the DC-DC converter. With ceramic capacitors, the voltage ripple from ESL is negligible.
PAGE 14
MAX1973/MAX1974 Smallest 1A, 1.4MHz Step-Down Regulators VOUT = 2.5V IOUT(MAX) = 1A COUT = 4.7µF PC Board Layout A properly designed PC board layout is important in any switching regulator. The switching power stage requires particular attention. Follow these guidelines for good PC board layout: 1) Place decoupling capacitors as close to IC pins as possible. Keep the power ground plane (connected to PGND) and signal ground plane (connected to GND) separate.
PAGE 15
Smallest 1A, 1.4MHz Step-Down Regulators 10LUMAX.EPS e 4X S 10 INCHES 10 H ÿ 0.50±0.1 0.6±0.1 1 1 0.6±0.1 BOTTOM VIEW TOP VIEW D2 MILLIMETERS MAX DIM MIN 0.043 A 0.006 0.002 A1 A2 0.030 0.037 0.116 0.120 D1 0.114 0.118 D2 0.116 E1 0.120 E2 0.114 0.118 H 0.187 0.199 L 0.0157 0.0275 L1 0.037 REF b 0.007 0.0106 e 0.0197 BSC c 0.0035 0.0078 0.0196 REF S α 0∞ 6∞ MAX MIN 1.10 0.05 0.15 0.75 0.95 3.05 2.95 3.00 2.89 3.05 2.95 2.89 3.00 4.75 5.05 0.40 0.70 0.940 REF 0.177 0.270 0.500 BSC 0.090 0.