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General Description

The MAX1901/MAX1902/MAX1904 are buck-topology,

step-down, switch-mode, power-supply controllers that

generate logic-supply voltages in battery-powered sys-

tems. These high-performance, dual/triple-output devices

include on-board power-up sequencing, power-good sig-

naling with delay, digital soft-start, secondary winding

control, low dropout circuitry, internal frequency-compen-

sation networks, and automatic bootstrapping.

Up to 97% efficiency is achieved through synchronous

rectification and Maxim’s proprietary Idle Mode™ control

scheme. Efficiency is greater than 80% over a 1000:1

load-current range, which extends battery life in system

suspend or standby mode. Excellent dynamic response

corrects output load transients within five clock cycles.

Strong 1A on-board gate drivers ensure fast external N-

channel MOSFET switching.

These devices feature a logic-controlled and synchroniz-

able, fixed-frequency, pulse-width modulation (PWM)

operating mode. This reduces noise and RF interference

in sensitive mobile communications and pen-entry appli-

cations. Asserting the SKIP pin enables fixed-frequency

mode, for lowest noise under all load conditions.

The MAX1901/MAX1902/MAX1904 include two PWM reg-

ulators, adjustable from 2.5V to 5.5V with fixed 5.0V and

3.3V modes. All these devices include secondary feed-

back regulation, and the MAX1902 contains a 12V/120mA

linear regulator. The MAX1901/MAX1904 include a sec-

ondary feedback input (SECFB), plus a control pin

(STEER) that selects which PWM (3.3V or 5V) receives the

secondary feedback signal. SECFB provides a method

for adjusting the secondary winding voltage regulation

point with an external resistor divider, and is intended to

aid in creating auxiliary voltages other than fixed 12V.

The MAX1901/MAX1902 contain internal output overvolt-

age and undervoltage protection features.

________________________Applications

Notebook and Subnotebook Computers

PDAs and Mobile Communicators

Desktop CPU Local DC-DC Converters

Features

♦ 97% Efficiency

♦ 4.2V to 30V Input Range

♦ 2.5V to 5.5V Dual Adjustable Outputs

♦ Selectable 3.3V and 5V Fixed or Adjustable

Outputs (Dual Mode™)

♦ 12V Linear Regulator

♦ Adjustable Secondary Feedback

(MAX1901/MAX1904)

♦ 5V/50mA Linear Regulator Output

♦ Precision 2.5V Reference Output

♦ Programmable Power-Up Sequencing

♦ Power-Good (RESET) Output

♦ Output Overvoltage Protection

(MAX1901/MAX1902)

♦ Output Undervoltage Shutdown

(MAX1901/MAX1902)

♦ 333kHz/500kHz Low-Noise, Fixed-Frequency

Operation

♦ Low-Dropout, 98% Duty-Factor Operation

♦ 2.5mW Typical Quiescent Power (12V input, both

SMPSs on)

♦ 4µA Typical Shutdown Current

MAX1901/MAX1902/MAX1904

500kHz Multi-Output, Low-Noise Power-Supply

Controllers for Notebook Computers

________________________________________________________________ Maxim Integrated Products 1

LINEAR

12V

LINEAR

POWER-UP

SEQUENCE

POWER-

GOOD

3.3V

SMPS

RESETON/OFF

5V (RTC)

3.3V

INPUT

12V

Functional Diagram

19-2224; Rev 3; 12/03

Ordering Information

Idle Mode is a trademark of Maxim Integrated Products, Inc.

Dual Mode is a trademark of Maxim Integrated Products, Inc.

Pin Configurations appear at end of data sheet.

PART TEMP RANGE PIN-PACKAGE

MAX1901EAI -40°C to +85°C 28 SSOP

MAX1901ETJ -40°C to +85°C32 Thin QFN 5m m x 5m m

MAX1902EAI -40°C to +85°C 28 SSOP

MAX1902ETJ -40°C to +85°C32 Thin QFN 5m m x 5m m

MAX1904EAI -40°C to +85°C 28 SSOP

MAX1904ETJ -40°C to +85°C32 Thin QFN 5m m x 5m m

Summary of content (33 pages)

PAGE 1
9-2224; Rev 3; 12/03 500kHz Multi-Output, Low-Noise Power-Supply Controllers for Notebook Computers The MAX1901/MAX1902/MAX1904 include two PWM regulators, adjustable from 2.5V to 5.5V with fixed 5.0V and 3.3V modes. All these devices include secondary feedback regulation, and the MAX1902 contains a 12V/120mA linear regulator. The MAX1901/MAX1904 include a secondary feedback input (SECFB), plus a control pin (STEER) that selects which PWM (3.3V or 5V) receives the secondary feedback signal.
PAGE 2
MAX1901/MAX1902/MAX1904 500kHz Multi-Output, Low-Noise Power-Supply Controllers for Notebook Computers ABSOLUTE MAXIMUM RATINGS V+ to GND ..............................................................-0.3V to +36V PGND to GND.....................................................................±0.3V VL to GND ................................................................-0.3V to +6V BST3, BST5 to GND ..............................................-0.3V to +36V CSH3, CSH5 to GND.............................
PAGE 3
500kHz Multi-Output, Low-Noise Power-Supply Controllers for Notebook Computers (V+ = 15V, both PWMs on, SYNC = VL, VL load = 0, REF load = 0, SKIP = 0, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER MIN TYP 95 97 SYNC = 0 (Note 2) 96.
PAGE 4
MAX1901/MAX1902/MAX1904 500kHz Multi-Output, Low-Noise Power-Supply Controllers for Notebook Computers ELECTRICAL CHARACTERISTICS (continued) (V+ = 15V, both PWMs on, SYNC = VL, VL load = 0, REF load = 0, SKIP = 0, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.
PAGE 5
00kHz Multi-Output, Low-Noise Power-Supply Controllers for Notebook Computers (V+ = 15V, both PWMs on, SYNC = VL, VL load = 0, REF load = 0, SKIP = 0, TA = -40°C to +85°C, unless otherwise noted.) (Note 7) PARAMETER CONDITIONS MIN TYP MAX UNITS 4.2 30.0 V MAIN SMPS CONTROLLERS Input Voltage Range 3V Output Voltage in Adjustable Mode V+ = 4.2V to 30V, CSH3 - CSL3 = 0, CSL3 tied to FB3 2.42 2.58 V 3V Output Voltage in Fixed Mode V+ = 4.2V to 30V, 0 < CSH3 - CSL3 < 80mV, FB3 = 0 3.20 3.
PAGE 6
MAX1901/MAX1902/MAX1904 500kHz Multi-Output, Low-Noise Power-Supply Controllers for Notebook Computers ELECTRICAL CHARACTERISTICS (continued) (V+ = 15V, both PWMs on, SYNC = VL, VL load = 0, REF load = 0, SKIP = 0, TA = -40°C to +85°C, unless otherwise noted.) (Note 7) PARAMETER CONDITIONS MIN TYP MAX UNITS V+ Standby Supply Current V+ = 5.5V to 30V, both SMPSs off, includes current into SHDN 60 µA V+ Standby Supply Current in Dropout V+ = 4.2V to 5.
PAGE 7
500kHz Multi-Output, Low-Noise Power-Supply Controllers for Notebook Computers V+ = 15V 75 70 65 55 50 0.001 75 70 60 ON5 = ON3 = 5V f = 500kHz MAX1901/MAX1904 55 50 0.01 0.1 1 10 0.01 0.1 1 0 10 5 10 15 20 INPUT VOLTAGE (V) NO LOAD INPUT CURRENT vs. INPUT VOLTAGE V+ STANDBY INPUT CURRENT vs. INPUT VOLTAGE SHUTDOWN INPUT CURRENT vs. INPUT VOLTAGE INPUT CURRENT (µA) 1 SKIP = 0V 1000 100 SHDN = 0V 8 10 0 1 15 20 25 4 ON5 = ON3 = 0V NO LOAD 0.
PAGE 8
Typical Operating Characteristics (continued) (Circuit of Figure 1, Table 1, 6A/500kHz components, TA = +25°C, unless otherwise noted.) REF OUTPUT VOLTAGE vs. OUTPUT CURRENT STARTUP WAVEFORMS MAX1901 toc11 MAX1901 toc10 2.505 VIN = 15V ON3 = ON5 = 0 REF OUTPUT VOLTAGE (V) MAX1901/MAX1902/MAX1904 500kHz Multi-Output, Low-Noise Power-Supply Controllers for Notebook Computers RUN 5V/div 0 2.500 3.3V OUTPUT 2V/div 0 2.495 TIME 2V/div 0 2.490 5V OUTPUT 5V/div 0 2.
PAGE 9
500kHz Multi-Output, Low-Noise Power-Supply Controllers for Notebook Computers PIN SSOP 1 QFN 29 2 30 3 4 5 31 1 NAME FUNCTION CSH3 Current-Sense Input for the 3.3V SMPS. Current-limit level is 100mV referred to CSL3. CSL3 Current-Sense Input. Also serves as the feedback input in fixed-output mode. FB3 Feedback Input for the 3.3V SMPS. Regulates at FB3 = REF (approx. 2.5V) in adjustable mode. FB3 is a dual-mode input that also selects the 3.
PAGE 10
500kHz Multi-Output, Low-Noise Power-Supply Controllers for Notebook Computers MAX1901/MAX1902/MAX1904 Pin Description (continued) PIN QSOP 10 QFN NAME FUNCTION 15 13 SEQ Pin-strap input that selects the SMPS power-up sequence: SEQ = GND: 5V before 3.3V, RESET output determined by both outputs SEQ = REF: Separate ON3/ON5 controls, RESET output determined by 3.3V output SEQ = VL: 3.
PAGE 11
500kHz Multi-Output, Low-Noise Power-Supply Controllers for Notebook Computers 5V ALWAYS ON 7V TO 24V C3 10Ω 4.7µF 0.1µF 0.1µF V+ SHDN SECFB VL 4.7µF Q1 C4 0.1µF R1 5V OUTPUT C1 BST3 DH5 C5 0.1µF 0.1µF LX5 Q2 Q3 DH3 0.1µF L1 * SYNC BST5 L2 LX3 DL5 MAX1901 MAX1904 DL3 GND PGND CSH5 CSH3 CSL5 CSL3 R2 3.3V OUTPUT * C2 Q4 FB3 FB5 RESET 5V ON/OFF TIME/ON5 3.3V ON/OFF RUN/ON3 RESET OUTPUT SKIP STEER SEQ REF 2.
PAGE 12
MAX1901/MAX1902/MAX1904 500kHz Multi-Output, Low-Noise Power-Supply Controllers for Notebook Computers Standard Application Circuit Detailed Description The basic MAX1901/MAX1904 dual-output 3.3V/5V buck converter (Figure 1) is easily adapted to meet a wide range of applications with inputs up to 28V by substituting components from Table 1.
PAGE 13
500kHz Multi-Output, Low-Noise Power-Supply Controllers for Notebook Computers MANUFACTURER USA PHONE FACTORY FAX Dale-Vishay 402-564-3131 402-563-6418 Fairchild Semiconductor 408-721-2181 408-721-1635 International Rectifier 310-322-3331 310-322-3332 Sanyo 619-661-6835 619-661-1055 Sumida 847-956-0666 847-956-0702 Taiyo Yuden 408-573-4150 408-573-4159 The MAX1901/MAX1902/MAX1904 contain ten major circuit blocks (Figure 2).
PAGE 14
INPUT 7V to 24V SHDN V+ SYNC CSL5 + MAX1902 4.5V ON/OFF 5V ALWAYS ON 12V LINEAR REG 5V LINEAR REG VL REF VDD + - 13V DH3 3.3V 12V IN SECFB 2.5V REF BST3 12OUT BST5 RAW 15V DH5 LX3 VL DL3 3.3V PWM LOGIC 5V PWM LOGIC 333kHz TO 500kHz OSC LX5 VL 5V DL5 PGND OV/UV FAULT CSH3 CSL3 + REF - REF 1.75V 2.68V LPF 50kHz CSH5 CSL5 + LPF 50kHz 2.388V FB3 - R3 FB5 OUTPUTS UP - R2 - + + R1 - + R4 + 0.6V 0.
PAGE 15
500kHz Multi-Output, Low-Noise Power-Supply Controllers for Notebook Computers 1X CSL_ REF FROM FEEDBACK DIVIDER MAIN PWM COMPARATOR BST_ R LEVEL SHIFT Q S DH_ LX_ SLOPE COMP OSC 30mV SKIP CURRENT LIMIT DAC SHOOTTHROUGH CONTROL CK COUNTER SHDN SOFT-START SYNCHRONOUS RECTIFIER CONTROL R -100mV S VL Q LEVEL SHIFT DL_ PGND REF 0.75µs SINGLE-SHOT SECFB Figure 3.
PAGE 16
MAX1901/MAX1902/MAX1904 500kHz Multi-Output, Low-Noise Power-Supply Controllers for Notebook Computers Table 3.
PAGE 17
500kHz Multi-Output, Low-Noise Power-Supply Controllers for Notebook Computers Boost High-Side Gate-Drive Supply (BST3 and BST5) Gate-drive voltage for the high-side N-channel switches is generated by a flying-capacitor boost circuit (Figure 2). The capacitor between BST_ and LX_ is alternately charged from the VL supply and placed parallel to the high-side MOSFET’s gate-source terminals. On startup, the synchronous rectifier (low-side MOSFET) forces LX_ to 0V and charges the boost capacitors to 5V.
PAGE 18
MAX1901/MAX1902/MAX1904 500kHz Multi-Output, Low-Noise Power-Supply Controllers for Notebook Computers RESET Power-Good Voltage Monitor The power-good monitor generates a system RESET signal. At first power-up, RESET is held low until both the 3.3V and 5V SMPS outputs are in regulation. At this point, an internal timer begins counting oscillator pulses, and RESET continues to be held low until 32,000 cycles have elapsed.
PAGE 19
500kHz Multi-Output, Low-Noise Power-Supply Controllers for Notebook Computers Internal Digital Soft-Start Circuit Soft-start allows a gradual increase of the internal current-limit level at startup to reduce input surge currents. Both SMPSs contain internal digital soft-start circuits, each controlled by a counter, a digital-to-analog converter (DAC), and a current-limit comparator. In shutdown or standby mode, the soft-start counter is reset to zero.
PAGE 20
MAX1901/MAX1902/MAX1904 500kHz Multi-Output, Low-Noise Power-Supply Controllers for Notebook Computers tor (primary) current, pulling current from the output filter capacitor and causing the flyback transformer to operate in forward mode. The low impedance presented by the transformer secondary in forward mode dumps current into the secondary output, charging up the secondary capacitor and bringing VDD or SECFB back into regulation.
PAGE 21
500kHz Multi-Output, Low-Noise Power-Supply Controllers for Notebook Computers Inductor Value The exact inductor value isn’t critical and can be freely adjusted to make trade-offs between size, cost, and efficiency. Lower inductor values minimize size and cost, but reduce efficiency due to higher peak-current levels. The smallest inductor is achieved by lowering the inductance until the circuit operates at the border between continuous and discontinuous mode.
PAGE 22
MAX1901/MAX1902/MAX1904 500kHz Multi-Output, Low-Noise Power-Supply Controllers for Notebook Computers IRMS = ILOAD × VOUT (VIN - VOUT ) VIN Therefore, when VIN is 2 x VOUT: I IRMS = LOAD 2 Bypassing V+ Bypass the V+ input with a 4.7µF tantalum capacitor paralleled with a 0.1µF ceramic capacitor, close to the IC. A 10Ω series resistor to VIN is also recommended. Bypassing VL Bypass the VL output with a 4.7µF tantalum capacitor paralleled with a 0.1µF ceramic capacitor, close to the device.
PAGE 23
500kHz Multi-Output, Low-Noise Power-Supply Controllers for Notebook Computers LPRIMARY = VOUT (VIN(MAX) - VOUT ) VIN(MAX) × f × ITOTAL × LIR Turns Ratio N = VSEC + VFWD VOUT(MIN) + VRECT + VSENSE where: VSEC = the minimum required rectified sec ondary output voltage VFWD = the forward drop across the secondary rectifier VOUT(MIN) = the minimum value of the main out put voltage (from the Electrical Characteristics tables) VRECT = the on-state voltage drop across the synchronous rectifier MOSFET VSENSE
PAGE 24
MAX1901/MAX1902/MAX1904 500kHz Multi-Output, Low-Noise Power-Supply Controllers for Notebook Computers Use a Schottky diode with a DC current rating equal to one third of the load current. The Schottky diode’s rated reverse breakdown voltage must be at least equal to the maximum input voltage, preferably with a 20% derating factor. Boost-Supply Diode A signal diode such as a 1N4148 works well in most applications.
PAGE 25
500kHz Multi-Output, Low-Noise Power-Supply Controllers for Notebook Computers SYMPTOM CONDITION ROOT CAUSE SOLUTION Sag or droop in VOUT under step-load change Low VIN - VOUT differential, <1.5V Limited inductor-current slew rate per cycle. Increase bulk output capacitance per formula (see the Low-Voltage Operation section). Reduce inductor value. Dropout voltage is too high (VOUT follows VIN as VIN decreases) Low VIN - VOUT differential, <1V Maximum duty-cycle limits exceeded.
PAGE 26
MAX1901/MAX1902/MAX1904 500kHz Multi-Output, Low-Noise Power-Supply Controllers for Notebook Computers Lossless-Inductor Current-Sensing Reduced Output Capacitance Application The DC resistance (DCR) of the inductor can be used to sense inductor current to improve the efficiency and to reduce the cost by eliminating the sense resistor. Figure 7 shows the sense circuit, where L is the inductance, RL is the inductor DCR, RS, and CS form an RC low-pass sense network.
PAGE 27
500kHz Multi-Output, Low-Noise Power-Supply Controllers for Notebook Computers • Priority 2: Minimize ground trace lengths in the high-current paths (discussed below). • Priority 3: Minimize other trace lengths in the high current paths.
PAGE 28
MAX1901/MAX1902/MAX1904 500kHz Multi-Output, Low-Noise Power-Supply Controllers for Notebook Computers * TO 3.3V OUTPUT * TO 5V OUTPUT INPUT 6.5V TO 28V C3 C4 10Ω 4.7µF 0.1µF 5V ALWAYS ON 22 6 0.1µF 21 4.7µF V+ SYNC VL ON/OFF 23 SHDN 12OUT VDD D1 25 Q1 27 L1 3.3V OUTPUT (3A) C1 * R1 BST5 BST3 12V AT 120mA 4 2.2µF 5 D2 D5 18 2.2µF 16 Q3 DH3 DH5 LX3 LX5 17 DL5 19 PGND 20 R2 0.1µF 26 0.
PAGE 29
500kHz Multi-Output, Low-Noise Power-Supply Controllers for Notebook Computers * MAX1901/MAX1902/MAX1904 ON/OFF * INPUT 6V TO 24V 5V ALWAYS ON C3 10Ω 0.1µF 4.7µF V+ SHDN SECFB VL 4.7µF BST5 Q1 5V OUTPUT * R1 0.1µF L1 DH3 0.1µF Q3 0.1µF LX5 LX3 DL5 MAX1901 DL3 MAX1904 Q2 C1 0.1µF BST3 DH5 1N5819 L2 Q4 3.
PAGE 30
Selector Guide DEVICE AUXILLARY OUTPUT OVER/UNDERVOLTAGE PROTECTION SECONDARY FEEDBACK MAX1901 None (SECFB input) Selectable (STEER pin) Yes MAX1902 12V Linear Regulator Feeds into the 5V SMPS Yes MAX1904 None (SECFB input) Selectable (STEER pin) No Pin Configurations TOP VIEW CSH3 1 28 RUN/ON3 CSH3 1 28 RUN/ON3 CSL3 2 27 DH3 CSL3 2 27 DH3 FB3 3 26 LX3 FB3 3 26 LX3 12OUT 4 VDD 5 25 BST3 STEER 4 24 DL3 SECFB 5 MAX1902 SYNC 6 25 BST3 23 SHDN TIME/ON5 7 22 V+ TIME/ON5 7
PAGE 31
500kHz Multi-Output, Low-Noise Power-Supply Controllers for Notebook Computers SSOP.EPS 2 1 INCHES E H MILLIMETERS DIM MIN MAX MIN MAX A 0.068 0.078 1.73 1.99 A1 0.002 0.008 0.05 0.21 B 0.010 0.015 0.25 0.38 C D 0.20 0.09 0.004 0.008 SEE VARIATIONS E 0.205 e 0.212 0.0256 BSC 5.20 MILLIMETERS INCHES D D D D D 5.38 MIN MAX MIN MAX 0.239 0.239 0.278 0.249 0.249 0.289 6.07 6.07 7.07 6.33 6.33 7.33 0.317 0.397 0.328 0.407 8.07 10.07 8.33 10.
PAGE 32
Package Information (continued) (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.) D2 0.15 C A D b CL 0.10 M C A B D2/2 D/2 PIN # 1 I.D. QFN THIN.EPS MAX1901/MAX1902/MAX1904 500kHz Multi-Output, Low-Noise Power-Supply Controllers for Notebook Computers k 0.15 C B PIN # 1 I.D. 0.35x45∞ E/2 E2/2 CL (NE-1) X e E E2 k L DETAIL A e (ND-1) X e CL CL L L e e 0.
PAGE 33
500kHz Multi-Output, Low-Noise Power-Supply Controllers for Notebook Computers COMMON DIMENSIONS EXPOSED PAD VARIATIONS NOTES: 1. DIMENSIONING & TOLERANCING CONFORM TO ASME Y14.5M-1994. 2. ALL DIMENSIONS ARE IN MILLIMETERS. ANGLES ARE IN DEGREES. 3. N IS THE TOTAL NUMBER OF TERMINALS. 4. THE TERMINAL #1 IDENTIFIER AND TERMINAL NUMBERING CONVENTION SHALL CONFORM TO JESD 95-1 SPP-012. DETAILS OF TERMINAL #1 IDENTIFIER ARE OPTIONAL, BUT MUST BE LOCATED WITHIN THE ZONE INDICATED.