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General Description

The MAX1637 synchronous, buck, switch-mode power-

supply controller generates the CPU supply voltage in

battery-powered systems. The MAX1637 is a stripped-

down version of the MAX1636 in a smaller 16-pin QSOP

package. The MAX1637 is intended to be powered sep-

arately from the battery by an external bias supply (typi-

cally the +5V system supply) in applications where the

battery exceeds 5.5V. The MAX1637 achieves excellent

DC and AC output voltage accuracy. This device can

operate from a low input voltage (3.15V) and delivers the

excellent load-transient response needed by upcoming

generations of dynamic-clock CPUs.

Using synchronous rectification, the MAX1637 achieves

up to 95% efficiency. 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 caused by the

latest dynamic-clock CPUs within five 300kHz clock

cycles. Powerful 1A on-board gate driv-ers ensure fast

external N-channel MOSFET switching.

The MAX1637 features a logic-controlled and synchro-

nizable, 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. For a

stand-alone device that includes a +5V VL linear regula-

tor and low-dropout capabilities, refer to the MAX1636

data sheet.

_________________________Applications

Notebook Computers Subnotebook Computers

Handy-Terminals, PDAs

____________________________Features

♦ ±2% DC Accuracy

♦ 0.1% (typ) DC Load Regulation

♦ Adjustable Switching Frequency to 350kHz

♦ Idle Mode™ Pulse-Skipping Operation

♦ 1.10V to 5.5V Adjustable Output Voltage

♦ 3.15V Minimum IC Supply Voltage (at V

pin)

♦ Internal Digital Soft-Start

♦ 1.1V ±2% Reference Output

♦ 1μA Total Shutdown Current

♦ Output Overvoltage Crowbar Protection

♦ Output Undervoltage Shutdown (foldback)

♦ Tiny 16-Pin QSOP Package

MAX1637

Miniature, Low-Voltage,

Precision Step-Down Controller

________________________________________________________________ Maxim Integrated Products 1

CSH SKIP

BST

PGND

TOP VIEW

MAX1637

QSOP

CSL

SHDN

REF

SYNC

GND

A "+" SIGN WILL REPLACE THE FIRST PIN INDICATOR ON LEAD-FREE PACKAGES.

__________________Pin Configuration

__________Typical Operating Circuit

19-1321; Rev 2; 8/05

EVALUATION KIT

AVAILABLE

______________Ordering Information

Idle Mode is a trademark of Maxim Integrated Products.

MAX1637

SHDN

GND

BATT

BIAS

PGND

BST

CSH

CSL

SKIP

SYNC

REF

OUTPUT

+Denotes lead-free package.

PART TEMP RANGE

PIN-PACKAGE

MAX1637EEE 40°C to +85°C 16 QSOP

MAX1637EEE+ 40°C to +85°C 16 QSOP

Summary of content (20 pages)

PAGE 1
9-1321; Rev 2; 8/05 KIT ATION EVALU E L B A IL AVA Miniature, Low-Voltage, Precision Step-Down Controller ____________________________Features The MAX1637 synchronous, buck, switch-mode powersupply controller generates the CPU supply voltage in battery-powered systems. The MAX1637 is a strippeddown version of the MAX1636 in a smaller 16-pin QSOP package.
PAGE 2
MAX1637 Miniature, Low-Voltage, Precision Step-Down Controller ABSOLUTE MAXIMUM RATINGS GND to PGND .............................................................+2V to -2V LX, BST to GND......................................................-0.3V to +36V BST, DH to LX...........................................................-0.3V to +6V VCC, VGG, CSL, CSH, SHDN to GND.......................-0.3V to +6V DL to GND..................................................-0.3V to (VGG + 0.
PAGE 3
Miniature, Low-Voltage, Precision Step-Down Controller (Circuit of Figure 1, VCC = VGG = 5V, SYNC = VCC, IREF = 0mA, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.
PAGE 4
ELECTRICAL CHARACTERISTICS (continued) (Circuit of Figure 1, VCC = VGG = 5V, SYNC = VCC, IREF = 0mA, TA = -40°C to +85°C, unless otherwise noted.) (Note 2) PARAMETER CONDITIONS MIN TYP MAX UNITS 4.0 10 % 60 80 % OVERVOLTAGE PROTECTION Overvoltage Trip Threshold FB, with respect to regulation point Output Undervoltage Lockout Threshold % of nominal output INPUTS AND OUTPUTS Logic Input Voltage High SHDN, SKIP, SYNC Logic Input Voltage Low SHDN, SKIP, SYNC 2.4 V 0.
PAGE 5
Miniature, Low-Voltage, Precision Step-Down Controller REF LOAD-REGULATION ERROR vs. REF LOAD CURRENT 4 2 0 -2 -4 -6 900 0.5 800 DROPOUT VOLTAGE (mV) 6 0.6 MAX1637-09 LOAD REGULATION ΔVOUT (mV) 8 REF LOAD REGULATION ΔV (mV) MAX1637-08 10 DROPOUT VOLTAGE vs. LOAD CURRENT 0.4 0.3 0.2 MAX1637-10 LOAD REGULATION vs. LOAD CURRENT VOUT FORCED TO 3.27V SYNC = VCC 700 MAX1637 ____________________________________Typical Operating Characteristics (continued) (VOUT = 3.
PAGE 6
MAX1637 Miniature, Low-Voltage, Precision Step-Down Controller ____________________________________Typical Operating Characteristics (continued) (VOUT = 3.3V, TA = +25°C, unless otherwise noted.) OVERVOLTAGE-PROTECTION WAVEFORMS (VIN SHORTED TO VOUT THROUGH A 0.5Ω RESISTOR) TIME EXITING SHUTDOWN (VOUT = 3.
PAGE 7
Miniature, Low-Voltage, Precision Step-Down Controller MAX1637 VBIAS +5V NOMINAL VBATT 20Ω VCC 4.7μF SYNC VGG 0.1μF C1 MAX1637 470pF CC CMPSH-3 BST DH Q1 0.1μF REF L1 R1 OUTPUT LX 1μF SKIP DL GND PGND Q2 C2 * CSH CSL 1M** R2 ON/OFF SHDN FB 0.01μF** R3 *SEE RECTIFIER CLAMP DIODE SECTION **OPTIONAL RC NETWORK FOR POWER-ON-RESET Figure 1.
PAGE 8
MAX1637 Miniature, Low-Voltage, Precision Step-Down Controller Table 1. Component Selection for Standard Applications LOAD CURRENT LOAD CURRENT COMPONENT 2A 3A (EV KIT) 7A (EV KIT) 3A Input Voltage Range 7V to 22V 7V to 22V 7V to 22V 4.75V to 30V Output Voltage Range 2.5V 2.5V 1.7V 3.
PAGE 9
Miniature, Low-Voltage, Precision Step-Down Controller MAX1637 VBATT VBIAS 3.15V TO 5.5V + VCC SKIP SYNC MAX1637 IC POWER VGG BST 200kHz TO 300kHz OSC DH LX PWM LOGIC DL PGND REF SHDN VOUT + 1.1V REF. SHUTDOWN CONTROL OFF + - REF UNDERVOLTAGE FAULT gm - OVERVOLTAGE FAULT - CC REF + VREF -30% ERROR INTEGRATOR + + - SLOPE COMPENSATION CSH CSL VREF +7% 60kHz LP FILTER FB GND Figure 2.
PAGE 10
MAX1637 Miniature, Low-Voltage, Precision Step-Down Controller CSH 1X CSL FB 2X REF REF gm CC BST R LEVEL SHIFT Q S DH LX OSC SLOPE COMPENSATION 30mV SKIP CURRENT LIMIT DAC SHOOTTHROUGH CONTROL CK SHDN COUNTER SOFT-START SYNCHRONOUS RECTIFIER CONTROL R -100mV VGG Q LEVEL SHIFT S DL PGND Figure 3.
PAGE 11
Miniature, Low-Voltage, Precision Step-Down Controller Fixed-Frequency Mode When SKIP is high, the controller always operates in fixed-frequency PWM mode for lowest noise. Each pulse from the oscillator sets the main PWM latch that turns on the high-side switch for a period determined by the duty factor (approximately VOUT / VIN). As the high-side switch turns off, the synchronous rectifier latch is set; 60ns later, the low-side switch turns on.
PAGE 12
MAX1637 Miniature, Low-Voltage, Precision Step-Down Controller REF, VCC, and VGG Supplies The 1.100V reference (REF) is accurate to ±2% over temperature, making REF useful as a precision system reference. Bypass REF to GND with a 0.22µF (min) capacitor. REF can supply up to 50µA for external loads. Loading REF reduces the main output voltage slightly because of the reference load-regulation error. The MAX1637 has two independent supply pins, VCC and VGG.
PAGE 13
Miniature, Low-Voltage, Precision Step-Down Controller Oscillator Frequency and Synchronization (SYNC) The SYNC input controls the oscillator frequency as follows: low selects 200kHz, high selects 300kHz. SYNC can also be used to synchronize with an external 5V CMOS or TTL clock generator. It has a guaranteed 240kHz to 340kHz capture range. A high-to-low transition on SYNC initiates a new cycle. Operation at 300kHz optimizes the application circuit for component size and cost.
PAGE 14
MAX1637 Miniature, Low-Voltage, Precision Step-Down Controller make prototype troubleshooting difficult since only 20ms or 30ms elapse before the SMPS is latched off. The overvoltage crowbar protection is disabled in output undervoltage mode. The exact time of the output rise depends on output capacitance and load current, but it is typically 1ms with a 300kHz oscillator. Output Overvoltage Protection The output voltage is set via a resistor divider connected to FB (Figure 1).
PAGE 15
Miniature, Low-Voltage, Precision Step-Down Controller L = VOUT(VIN(MAX) - VOUT) / (VIN(MIN) x ƒ x IOUT x LIR) where ƒ = switching frequency (normally 200kHz or 300kHz), and IOUT = maximum DC load current. The peak current can be calculated as follows: IPEAK = ILOAD + [VOUT(VIN(MAX) - VOUT) / (2 x ƒ x L x VIN(MAX))] The inductor’s DC resistance should be low enough that RDC x IPEAK < 100mV, as it is a key parameter for efficiency performance.
PAGE 16
MAX1637 Miniature, Low-Voltage, Precision Step-Down Controller Use only specialized low-ESR capacitors intended for switching-regulator applications, such as AVX TPS, Sprague 595D, Sanyo OS-CON, or Nichicon PL series. To ensure stability, the capacitor must meet both minimum capacitance and maximum ESR values as given in the following equations: COUT > VREF(1 + VOUT / VIN(MIN)) / VOUT x RSENSE x ƒ RESR < RSENSE x VOUT / VREF where RESR can be multiplied by 1.5, as discussed below.
PAGE 17
Miniature, Low-Voltage, Precision Step-Down Controller __________Applications Information Heavy-Load Efficiency Considerations The major efficiency-loss mechanisms under loads are as follows, in the usual order of importance: • P(I2R) = I2R losses • P(tran) = transition losses • P(gate) = gate-charge losses • P(diode) = diode-conduction losses • P(cap) = capacitor ESR losses • P(IC) = losses due to the IC’s operating supply current Inductor core losses are fairly low at heavy loads because the inductor’s AC
PAGE 18
MAX1637 Miniature, Low-Voltage, Precision Step-Down Controller P(gate) = Qg x ƒ x VGG where Qg is the sum of the gate-charge values for lowside and high-side switches. For matched MOSFETs, Q g is twice the data-sheet value of an individual MOSFET. Efficiency can usually be optimized by connecting VGG to the most efficient 5V source, such as the system +5V supply.
PAGE 19
Miniature, Low-Voltage, Precision Step-Down Controller MAX1637 VBIAS 3.15V TO 5.5V 4.7μF TANTALUM 20Ω 1μF VCC 220μF OS-CON VGG CMPSH-3 SYNC SKIP BST 0.1μF IRF7401 MAX1637 DH 10μH 20mΩ 1% OUTPUT = 2.5V AT 4A LX CDHR125-100 DL IRF7401 SHDN MBRS130 ON/OFF 130k 1% PGND 470μF LOW ESR TANTALUM CSH REF 1μF GND CSL CC FB 100k 1% 470pF Figure 7. 3.15V to 5.5V Single-Supply Application Circuit sensing at the supply’s output terminals without interference from IR drops and ground noise.
PAGE 20
________________________________________________________Package Information QSOP.EPS MAX1637 Miniature, Low-Voltage, Precision Step-Down Controller Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.