General Description
The MAX1572 is a fixed-frequency, synchronous step-
down DC-to-DC converter to power low-voltage micro-
processor/DSP cores in portable equipment requiring
high efficiency in a limited PC board area. The features
are optimized for high efficiency over a wide load range,
small external component size, low output ripple, and
excellent transient response. The input supply voltage
range is from 2.6V to 5.5V, while the output is internally
fixed from 0.75V to 2.5V in 50mV increments with a
guaranteed output current of 800mA. The high 2MHz
switching allows tiny low-cost capacitors and a low-pro-
file inductor, while the power-saving pulse-group mode
reduces quiescent current to 48µA (typ) with light loads.
To reduce noise and RF interference, the converter can
be configured to provide forced-PWM operation.
The MAX1572 includes a low on-resistance internal
MOSFET switch and synchronous rectifier to maximize
efficiency and minimize external component count. No
external diode is needed. Other features include soft-
start to eliminate inrush current at startup and a 170ms
(min) RESET output to provide power-on/undervoltage
reset. The MAX1572 is available in a 12-pin, 4mm x
4mm thin QFN package with exposed paddle.
Applications
Cell Phones and Smart Phones
PDAs, Palmtops, and Notebook Computers
MP3 and DVD Players
Digital Cameras and Camcorders
PCMCIA Cards
Hand-Held Instruments
Features
♦Up to 97% Efficiency
♦2MHz PWM Switching
♦800mA Guaranteed Output Current
♦Low 48µA Quiescent Current
♦Power-Saving Modes: Pulse-Group, Pulse-Skip,
Forced-PWM Mode
♦0.75V to 2.5V Preset Output Range
(in 50mV Increments)
♦Voltage-Positioning Load Transients
♦5mVP-P Output Ripple
♦Tiny 2.2µH Inductor
♦10µF Ceramic Output Capacitor
♦Low 0.1µA Shutdown Current
♦No External Schottky Diode Required
♦Soft-Start with Zero Inrush Current
♦170ms (min) RESET Output
♦Small 12-Pin, 4mm x 4mm Thin QFN Package
MAX1572
800mA, 2MHz, PWM DC-to-DC
Step-Down Converter with
RESET
________________________________________________________________ Maxim Integrated Products 1
MAX1572
12
11
10
789
PGND
LX
BATT
321
GND
SS
RESET
4
5
6
EN1
GND
ABATT
EN2
GND
OUT
4mm x 4mm
THIN QFN
TOP VIEW
Pin Configuration
Ordering Information
LX
2.2µH
PGND
OUT
RESET
GND
ABATT
EN1
BATT
MODE
SELECT
INPUT
2.6V TO 5.5V
OUTPUT
0.75V TO 2.5V
800mA
EN2
SS
MAX1572
Typical Operating Circuit
19-2837; Rev 1; 11/04
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.
*xyz is for the output voltage (e.g., MAX1572ETC165 has a
1.65V output). Minimum order quantity is 2500.
**EP = Exposed paddle.
EVALUATION KIT
AVAILABLE
PART TEMP RANGE PIN-PACKAGE
MAX1572ETC075
-40°C to +85°C12 Thin QFN-EP**
MAX1572ETC130
-40°C to +85°C12 Thin QFN-EP**
MAX1572ETC150
-40°C to +85°C12 Thin QFN-EP**
MAX1572ETC180
-40°C to +85°C12 Thin QFN-EP**
MAX1572ETC250
-40°C to +85°C12 Thin QFN-EP**
MAX1572ETCxyz*
-40°C to +85°C12 Thin QFN-EP**
Selector Guide appears at end of data sheet.
MAX1572
800mA, 2MHz, PWM DC-to-DC
Step-Down Converter with
RESET
2_______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VBATT = 3.6V, TA= +0°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ABATT, BATT, EN1, EN2, RESET, OUT,
SS to GND ............................................................-0.3V to +6V
PGND to GND .......................................................-0.3V to +0.3V
LX Current (Note 1) .............................................................±2.1A
Output Short-Circuit Duration ............................................Infinite
Continuous Power Dissipation (TA= +70°C)
12-Pin Thin QFN (derate 16.9mW/°C above +70°C)...1349mW
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature......................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
PARAMETER CONDITIONS MIN TYP MAX
UNITS
BATT Input Voltage 2.6 5.5 V
Undervoltage Lockout Threshold VBATT rising and falling, 1% hysteresis 2.20 2.35 2.55 V
EN1 = GND, EN2 = BATT, no switching 48 80
Quiescent Supply Current EN1 = BATT, EN2 = GND, no switching 700 µA
Shutdown Supply Current EN1 = EN2 = GND, TA = +25°C 0.1 1 µA
Maximum Output Current 800
mA
OUT Bias Current 69µA
No load, EN1 = EN2 = BATT 1.2 2.7
100mA load -0.4 +0.8 +2.0
300mA load 0
550mA load -1
Output-Voltage Accuracy
(Voltage Positioning)
800mA load -2
%
Line Regulation 0.3
%/V
VBATT = 3.6V 0.28 0.45
P-Channel On-Resistance
ILX = 180mA
VBATT = 2.6V 0.33 Ω
VBATT = 3.6V 0.18 0.30
N-Channel On-Resistance
ILX = 180mA
VBATT = 2.6V 0.20 Ω
P-Channel Current-Limit Threshold 1.00 1.25 1.65 A
N-Channel Current-Limit Threshold EN1 = EN2 = BATT -0.68 -0.52 -0.37 A
N-Channel Zero-Crossing Threshold EN1 = BATT, EN2 = GND 15 40 65
mA
LX Output Current (Note 2) 1.4
ARMS
LX Leakage Current EN1 = EN2 = GND 0.1 10 µA
Maximum Duty Cycle 100 %
EN1 = BATT, EN2 = GND or
EN1 = GND, EN2 = BATT 0
Minimum Duty Cycle
EN1 = EN2 = BATT 16.7 17.3
%
Switching Frequency 1.8 2 2.2
MHz
SS Output Impedance 65 100 150 kΩ
Note 1: LX has internal clamp diodes to PGND and BATT. Applications that forward bias these diodes should take care not to
exceed the IC’s package power dissipation limits.
MAX1572
800mA, 2MHz, PWM DC-to-DC
Step-Down Converter with
RESET
_______________________________________________________________________________________ 3
ELECTRICAL CHARACTERISTICS (continued)
(VBATT = 3.6V, TA= +0°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)
PARAMETER CONDITIONS MIN TYP MAX
UNITS
SS Discharge Resistance EN1 = EN2 = GND 100 200 Ω
VABATT > 4.2V 1.6
EN_ Logic Input High VABATT ≤ 4.2V 1.4 V
EN_ Logic Input Low 0.4 V
EN_ Logic Input Current 0.1 1 µA
RESET Threshold Percent of nominal, measured at OUT 87 90 93 %
RESET Timer Delay Time From VOUT > 90% to RESET = HI 170 200 230 ms
RESET Output Low Level ISINK = 1mA
0.015
0.075 V
RESET Internal Pullup Resistance to OUT 9 14 20 kΩ
Thermal-Shutdown Threshold TJ rising 160 °C
Thermal-Shutdown Hysteresis 20 °C
ELECTRICAL CHARACTERISTICS
(VBATT = 3.6V, TA= -40°C to +85°C, unless otherwise noted.) (Note 3)
PARAMETER CONDITIONS MIN TYP MAX
UNITS
BATT Input Voltage 2.6 5.5 V
Undervoltage Lockout Threshold VBATT rising and falling, 1% hysteresis 2.20 2.55 V
Quiescent Supply Current EN1 = GND, EN2 = BATT, no switching 80 µA
Shutdown Supply Current EN1 = EN2 = GND 3 µA
Maximum Output Current 800
mA
OUT Bias Current 9µA
No load, EN1 = EN2 = BATT 3.2
Output-Voltage Accuracy
(Voltage Positioning) 100mA load -1.2 +2.8 %
P-Channel On-Resistance ILX = 180mA 0.45 Ω
N-Channel On-Resistance ILX = 180mA 0.3 Ω
N-Channel Current-Limit Threshold EN1 = EN2 = BATT -0.68 -0.22 A
N-Channel Zero-Crossing Threshold EN1 = BATT, EN2 = GND 10 65
mA
LX Output Current (Note 2) 1.4
ARMS
LX Leakage Current EN1 = EN2 = GND 10 µA
Maximum Duty Cycle 100 %
Minimum Duty Cycle EN1 = EN2 = BATT 17.3 %
Switching Frequency 1.8 2.2
MHz
SS Output Impedance 65 150 kΩ
SS Discharge Resistance EN1 = EN2 = GND 200 Ω
VABATT > 4.2V 1.6
EN_ Logic Input High VABATT ≤ 4.2V 1.4 V
MAX1572
800mA, 2MHz, PWM DC-to-DC
Step-Down Converter with
RESET
4_______________________________________________________________________________________
ELECTRICAL CHARACTERISTICS (continued)
(VBATT = 3.6V, TA= -40°C to +85°C, unless otherwise noted.) (Note 2)
PARAMETER CONDITIONS MIN TYP MAX
UNITS
EN_ Logic Input Low 0.4 V
EN_ Logic Input Current 1µA
RESET Threshold Percent of nominal, measured at OUT 87 93 %
RESET Timer Delay Time From VOUT > 90% to RESET = HI 170 230 ms
RESET Output Low Level ISINK = 1mA 0.2 V
RESET Internal Pullup Resistance to OUT 9 20 kΩ
Note 2: Guaranteed by design, not production tested.
Note 3: Specifications to -40°C are guaranteed by design and not production tested.
Typical Operating Characteristics
(VBATT = 3.6V, VOUT = 1.5V, EN1 = GND, EN2 = BATT, TA= +25°C, unless otherwise noted.)
MAX1572
800mA, 2MHz, PWM DC-to-DC
Step-Down Converter with
RESET
_______________________________________________________________________________________ 5
HEAVY-LOAD SWITCHING WAVEFORMS
MAX1572 toc08
VLX
IL
VOUT
RIPPLE 10mV/div
500mA/div
2V/div
200ns/div
ILOAD = 500mA
LIGHT-LOAD SWITCHING WAVEFORMS
MAX1572 toc09
VLX
IL
VOUT
RIPPLE 20mV/div
500mA/div
2V/div
2µs/div
ILOAD = 20mA
SOFT-START/SHUTDOWN WAVEFORMS
MAX1572 toc10
VEN2
IIN
VOUT 1V/div
100mA/div
2V/div
200µs/div
RESET WAVEFORM
MAX1572 toc11
VEN2
IIN
VRESET
VOUT 1V/div
1V/div
100mA/div
2V/div
100ms/div
LOAD TRANSIENT, FORCED-PWM MODE
MAX1572 toc12
ILOAD
VOUT
500mA/div
100mV/div
4µs/div
ILOAD = 20mA TO 550mA
Typical Operating Characteristics (continued)
(VBATT = 3.6V, VOUT = 1.5V, EN1 = GND, EN2 = BATT, TA= +25°C, unless otherwise noted.)
MAX1572
800mA, 2MHz, PWM DC-to-DC
Step-Down Converter with
RESET
6_______________________________________________________________________________________
LOAD TRANSIENT, PULSE-SKIP MODE
MAX1572 toc13
ILOAD
VOUT
500mA/div
100mV/div
4µs/div
ILOAD = 20mA TO 550mA
LOAD TRANSIENT, PULSE-GROUP MODE
MAX1572 toc14
ILOAD
VOUT
500mA/div
100mV/div
4µs/div
ILOAD = 20mA TO 550mA
LINE TRANSIENT
MAX1572 toc15
IL
VIN
VOUT
200mA/div
20mV/div
1V/div
40µs/div
VIN = 3.5V TO 4.0V
Typical Operating Characteristics (continued)
(VBATT = 3.6V, VOUT = 1.5V, EN1 = GND, EN2 = BATT, TA= +25°C, unless otherwise noted.)
MAX1572
800mA, 2MHz, PWM DC-to-DC
Step-Down Converter with
RESET
_______________________________________________________________________________________ 7
Detailed Description
Figure 1 is the functional diagram.
PWM Control Scheme
The MAX1572 uses a 2MHz fixed-frequency, pulse-
width-modulated (PWM), current-mode control scheme.
The heart of the current-mode PWM controller is an
open-loop comparator that compares the error amp
voltage-feedback signal against the sum of the ampli-
fied current-sense signal and the slope compensation
ramp. At each rising edge of the internal clock, the
internal high-side P-channel MOSFET turns on until the
PWM comparator trips. During this on-time, current
ramps up through the inductor, sourcing current to the
Pin Description
PIN
NAME
FUNCTION
1
RESET
Active-Low RESET Output. Open-drain output with internal 14kΩ pullup to OUT. RESET is driven LOW in
shutdown.
2SS
Soft-Start Control. Connect a capacitor from SS to GND to set the soft-start time. Use a 1000pF or larger
capacitor to eliminate inrush current during startup. With greater than 10µF total output capacitance, increase
CSS to COUT/10,000 for soft-start. In shutdown, SS is discharged internally with 100Ω to GND.
3, 5, 11
GND Ground. Connect all ground pins to the exposed paddle.
4OUT Output Sense Input. Connect to the output of the regulator. In shutdown, OUT is discharged internally with
14kΩ to GND.
6EN2 Enable/Mode Control Input 2. See Table 1.
7
PGND
Power Ground. Connect to exposed paddle.
8LXInductor Connection. LX is high impedance in shutdown.
9
BATT
S up p l y V ol tag e Inp ut. C onnect to a 2.6V to 5.5V sour ce. C onnect a 10µF cer am i c cap aci tor fr om BATT to G N D .
10 EN1 Enable/Mode Control Input 1. See Table 1.
12
ABATT
Anal og S up p l y Inp ut. C onnect to BATT thr oug h a 10Ω r esi stor . C onnect a 0.1µF cap aci tor fr om ABATT to GN D .
—Exposed
Paddle
Exposed Paddle. Connect to GND and PGND.
Table 1. Mode Select Truth Table
MODE EN1 EN2
Shutdown 0 0
Pulse group 0 1
Pulse skip 1 0
Forced PWM 1 1
A zero represents EN_ being driven low or connected to GND.
A 1 represents EN_ being driven high or connected to BATT.
BATT
CLOCK
2MHz
PWM
CONTROL
ABATT
LX
10Ω
0.1µF
10µF
2.2µH
COUT
PGND
GND
OUT
SS
EA
RESET
THERMAL
SHUTDOWN
REFERENCE
OUTPUT
0.75V TO 2.5V
800mA
INPUT
2.6V TO 5.5V
MAX1572
1000pF
SLOPE
COMP
RESET
TIMER
170ms
EN1
EN2
CURRENT
SENSE
MODE
SELECT
Figure 1. Functional Diagram
MAX1572
800mA, 2MHz, PWM DC-to-DC
Step-Down Converter with
RESET
8_______________________________________________________________________________________
MANUFACTURER
PART
VALUE (µH)
RL (mΩ)I
SAT (mA) SIZE (mm) SHIELDED
Murata LQH32CN 2.2 97 790
2.5 x 3.2 x 2.0
No
CDRH3D16 2.2 50 1200
3.8 x 3.8 x 1.8
Yes
Sumida CDRH2D11 2.2 78 780
3.2 x 3.2 x 1.2
Yes
D312F 2.2 170 1200
3.6 x 3.6 x 1.2
No
TOKO D412F 2.2 140 1330
4.8 x 4.8 x 1.2
No
Table 2. Recommended Inductors
output and storing energy in the inductor’s magnetic
field. The current-mode feedback system regulates the
peak inductor current as a function of the output voltage
error signal. Since the average inductor current is nearly
the same as the peak inductor current (assuming that
the inductor value is relatively high to minimize ripple
current), the circuit acts as a switch-mode transconduc-
tance amplifier. This pushes the output LC filter pole,
normally found in a voltage-mode PWM, to a higher fre-
quency. To preserve inner-loop stability and eliminate
inductor staircasing, an internal slope-compensation
ramp is summed into the main PWM comparator. During
the second half of the switching cycle (off-time), the
internal high-side P-channel MOSFET turns off and the
internal low-side N-channel MOSFET turns on. Now the
inductor releases the stored energy as its current ramps
down while still providing current to the output. The output
capacitor stores charge when the inductor current
exceeds the load current and discharges when the
inductor current is lower, smoothing the voltage across
the load. Under overload conditions, when the inductor
current exceeds the current limit, the high-side MOSFET
is turned off and the low-side MOSFET remains on for
the remainder of the cycle to let the inductor current
ramp down.
Pulse-Group Mode
Pulse-group mode is used to minimize the supply cur-
rent with a light load. In pulse-group mode, the IC shuts
off most internal circuitry when VOUT is +0.8% above
nominal regulation. When VOUT drops below +0.8% of
the nominal regulation voltage, the IC powers up its cir-
cuits and resumes switching.
Pulse-Skip Mode
Pulse-skip mode is also used to minimize the supply
current with a light load. The difference between pulse-
group and pulse-skip modes is that when VOUT rises
above the +0.8% regulation point, pulse-group mode
stops switching and completely turns off a number of
circuits. Under the same conditions, pulse-skip mode
stops switching but leaves all circuits on. The delay
coming out of pulse-skip mode is shorter than with
pulse-group mode. In pulse-skip mode, the output volt-
age ripple is lower, and the load-transient response
faster. However, the quiescent current is higher than in
pulse-group mode.
Forced-PWM Mode
In forced-PWM mode, the MAX1572 operates at a con-
stant 2MHz switching frequency without pulse skipping.
This is desirable in noise-sensitive applications, since the
output ripple is minimized and has a predictable noise
spectrum. Forced-PWM mode requires higher supply
current with light loads due to constant switching.
100% Duty-Cycle Operation
The MAX1572 can operate at 100% duty cycle. In this
state, the high-side P-channel MOSFET is turned on (not
switching). This occurs when the input voltage is close to
the output voltage. The dropout voltage is the voltage
drop due to the output current across the on-resistance
of the internal P-channel MOSFET (RDS(ON)P) and the
inductor resistance (RL):
VDROPOUT = IOUT ×( RDS(ON)P + RL )
RDS(ON)P is given in the Electrical Characteristics sec-
tion. RL, for a few recommended inductors, is given in
Table 2.
Load-Transient Response/
Voltage Positioning
The MAX1572 uses voltage positioning that matches
the load regulation to the voltage droop seen during
load transients. In this way, the output voltage does not
overshoot when the load is removed, which results in
the total output-voltage variation being half as wide as
in a conventional design. Figure 2 shows an example of
a voltage-positioned and a nonvoltage-positioned load
transient. Additionally, the MAX1572 uses a wide-band-
width feedback loop to respond more quickly to a load
transient than regulators using conventional integrating
feedback loops.
The load line used to achieve voltage positioning is
shown in Figure 3. This assumes a nominal operating
point of 3.6V input at 300mA load.
MAX1572
800mA, 2MHz, PWM DC-to-DC
Step-Down Converter with
RESET
_______________________________________________________________________________________ 9
Soft-Start
Soft-start is used to prevent input-current overshoot dur-
ing startup. For most applications using a 10µF output
capacitor, connect a 1000pF capacitor from SS to GND.
If a larger output capacitor is used, then use the follow-
ing formula to find the value of the soft-start capacitor
needed to prevent input-current overshoot:
CSS = COUT /104
During soft-start, the output voltage rises from 0 to
VOUT(nom) with a time constant equal to CSS times
100kΩ(see the Typical Operating Characteristics).
170ms
RESET
RESET is an open-drain output with an internal 14kΩ
pullup resistor to OUT. During startup, RESET is held low
until 200ms (typ) after the output voltage reaches 90% of
its nominal regulation voltage. When the output voltage
drops below 90% of its nominal regulation voltage,
RESET pulls low again. See the Typical Operating
Characteristics section for RESET waveforms during
startup and shutdown.
Applications Information
Inductor Selection
A 2.2µH inductor with a saturation current of at least 1A
is recommended for full-load (800mA) applications. For
lower load currents, the inductor current rating may be
reduced. For most applications, use an inductor with a
current rating 1.25 times the maximum required output
current. For maximum efficiency, the inductor’s DC
resistance should be as low as possible. See Table 2
for recommended inductors and manufacturers.
Capacitor Selection
Ceramic 10µF input and output capacitors are recom-
mended for most applications. For output voltages
below 1.5V, output capacitance should be increased to
22µF. For best stability over a wide temperature range,
use capacitors with an X5R or better dielectric.
ABATT Input Filter
In normal applications, an RC filter on ABATT keeps
power-supply noise from entering the IC. Connect a
10Ωresistor between BATT and ABATT and connect a
0.1µF capacitor from ABATT to GND.
PC Board Layout and Routing
Due to fast-switching waveforms and high-current
paths, careful PC board layout is required. An evalua-
tion kit (MAX1572EVKIT) is available to speed design.
When laying out a board, minimize trace lengths
between the IC, the inductor, the input capacitor, and the
output capacitor. Keep these traces short, direct, and
wide. Keep noisy traces, such as the LX node trace,
away from OUT. The input bypass capacitors should be
placed as close to the IC as possible. Connect PGND
and GND directly to the exposed paddle underneath the
IC. The ground connections of the input and output
capacitors should be as close together as possible.
IOUT
VOUT
(CONVENTIONAL)
VOUT
(VOLTAGE POSITIONING)
Figure 2. Load Transient Response, With and Without Voltage
Positioning
CHANGE IN
OUTPUT
VOLTAGE (%)
NORMAL OPERATION
FORCED-PWM
VIN = 5.5V
VIN = 2.6V
+1
0
-1
-2
0200400 600 800
LOAD CURRENT (mA)
VIN = 3.6V
Figure 3. Voltage-Positioning Load Line
MAX1572
800mA, 2MHz, PWM DC-to-DC
Step-Down Converter with
RESET
10 ______________________________________________________________________________________
Chip Information
TRANSISTOR COUNT: 3697
PROCESS: BiCMOS
PART VOUT (V) TOP MARK
MAX1572ETC075
0.75 AABW
MAX1572ETC130
1.30 AACW
MAX1572ETC150
1.50 AABX
MAX1572ETC180
1.80 AABY
MAX1572ETC250
2.50 AABZ
MAX1572ETCxyz
*—
Selector Guide
*xyz is for output voltage (e.g., MAX1572ETC165 has a 1.65V
output).
Package Information
(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.)
24L QFN THIN.EPS
C1
2
21-0139
PACKAGE OUTLINE
12, 16, 20, 24L THIN QFN, 4x4x0.8mm
MAX1572
800mA, 2MHz, PWM DC-to-DC
Step-Down Converter with
RESET
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.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 11
©2004 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
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.)
C
2
2
21-0139
PACKAGE OUTLINE
12, 16, 20, 24L THIN QFN, 4x4x0.8mm