19-3336; Rev 3; 1/11
KIT
ATION
EVALU
E
BL
AVAILA
16µA I
Q
, 1.2A PWM
Step-Down DC-DC Converters
General Description
Features
o
Up to 97% Efficiency
o
95% Efficiency at 1mA Load Current
o
Low 16µA Quiescent Current
o
1MHz PWM Switching
o
Tiny 3.3µH Inductor
o
Selectable 3.3V, 2.5V, 1.8V, 1.5V, 1.3V, 1.2V, 1.0V,
and Adjustable Output
o
1.2A Guaranteed Output Current
(MAX1556/MAX1556A)
o
Voltage Positioning Optimizes Load-Transient
Response
o
Low 27µA Quiescent Current in Dropout
o
Low 0.1µA Shutdown Current
o
No External Schottky Diode Required
o
Analog Soft-Start with Zero Overshoot Current
o
Small, 10-Pin, 3mm x 3mm TDFN Package
MAX1556/MAX1556A/MAX1557
The MAX1556/MAX1556A/MAX1557 are low-operating-
current (16µA), fixed-frequency step-down regulators.
High efficiency, low-quiescent operating current, low
dropout, and minimal (27µA) quiescent current in
dropout make these converters ideal for powering
portable devices from 1-cell Li-ion or 3-cell alkaline/NiMH
batteries. The MAX1556 delivers up to 1.2A; has pin-
selectable 1.8V, 2.5V, and 3.3V outputs; and is also
adjustable. The MAX1557 delivers up to 600mA; has pin-
selectable 1V, 1.3V, and 1.5V outputs; and is also
adjustable.
The MAX1556/MAX1556A/MAX1557 contain a low-on-
resistance internal MOSFET switch and synchronous
rectifier to maximize efficiency and dropout perfor-
mance while minimizing external component count. A
proprietary topology offers the benefits of a high fixed-
frequency operation while still providing excellent effi-
ciency at both light and full loads. A 1MHz PWM
switching frequency keeps components small. Both
devices also feature an adjustable soft-start to minimize
battery transient loading.
The MAX1556/MAX1556A/MAX1557 are available in a
tiny 10-pin TDFN (3mm x 3mm) package.
Ordering Information
PART
MAX1556ETB+
MAX1556ETB/V+T
MAX1556AETB+
MAX1557ETB+
TEMP RANGE PIN-PACKAGE
-40°C to +85°C 10 TDFN-EP*
-40°C to +85°C 10 TDFN-EP*
-40°C to +85°C 10 TDFN-EP*
-40°C to +85°C 10 TDFN-EP*
TOP
MARK
ACQ
AWS
AUJ
ACR
Applications
PDAs and Palmtop Computers
Cell Phones and Smart Phones
Digital Cameras and Camcorders
Portable MP3 and DVD Players
Hand-Held Instruments
*EP
= Exposed paddle.
+Denotes
a lead(Pb)-free/RoHS-compliant package.
/V denotes an automotive qualified part.
T
= Tape and reel.
Typical Operating Circuit
INPUT
2.6V TO 5.5V
OUTPUT
0.75V TO V
IN
INP
LX
TOP VIEW
Pin Configuration
IN
VOLTAGE
SELECT
ON
OFF
D1
D2
MAX1556
MAX1556A
MAX1557
PGND
OUT
SS
IN
GND
SS
OUT
SHDN
1
2
3
4
5
TDFN
10
9
D1
INP
LX
MAX1556
MAX1556A
MAX1557
8
7
6
PGND
D2
SHDN
GND
________________________________________________________________
Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
16µA I
Q
, 1.2A PWM DC-DC
Step-Down Converters
MAX1556/MAX1556A/MAX1557
ABSOLUTE MAXIMUM RATINGS
IN, INP, OUT, D2,
SHDN
to GND ..........................-0.3V to +6.0V
SS, D1 to GND .............................................-0.3V to (V
IN
+ 0.3V)
PGND to GND .......................................................-0.3V to +0.3V
LX Current (Note 1)...........................................................±2.25A
Output Short-Circuit Duration.....................................Continuous
Continuous Power Dissipation (T
A
= +70°C)
10-Pin TDFN (derate 24.4mW/°C above +70°C) .......1951mW
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
Soldering Temperature (reflow) .......................................+260°C
Note 1:
LX has internal clamp diodes to GND and IN. Applications that forward bias these diodes should take care not to exceed
the IC’s package power-dissipation limits.
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.
ELECTRICAL CHARACTERISTICS
(V
IN
= V
INP
= V
SHDN
= 3.6V, T
A
= -40°C to +85°C. Typical values are at T
A
= +25°C, unless otherwise noted.) (Note 2)
PARAMETER
Input Voltage
Undervoltage-Lockout Threshold
Quiescent Supply Current
Shutdown Supply Current
Output Voltage Range
No load
300mA load
T
A
= 0°C to +85°C
(Note 3)
Output Accuracy
T
A
= -40°C to +85°C
(Note 3)
MAX1556/MAX1556A
MAX1557
D1 = D2 = GND
MAX1556/MAX1557
D1 = D2 = GND,
V
OUT
= 0.75V at
300mA (typ),
T
A
= 0°C to +85°C
MAX1556/MAX1557
D1 = D2 = GND,
V
OUT
= 0.75V
at 300mA (typ),
T
A
= -40°C to +85°C
MAX1556/MAX1557
T
A
= +25°C
T
A
= +85°C
No load
300mA load
600mA load
1200mA load, MAX1556 only
No load
300mA load
600mA load
1200mA load, MAX1556 only
-0.50
-1.2
-1.75
-3.25
-1.25
-1.75
-2.75
-4.25
600mA load
1200mA load, MAX1556
1200mA load, MAX1556A
No load
300mA load
600mA load
1200mA load, MAX1556
Maximum Output Current
-0.75
-1.5
-2.25
-4.0
1200
600
0.01
0.01
3
+0.75
0
-0.75
-2.25
4.5
+1.75
+1.2
+0.25
-1.25
+2.25
+1.50
+0.25
-1.00
%
0.1
µA
V
IN
rising and falling, 35mV hysteresis (typ)
No switching, D1 = D2 = GND
Dropout
SHDN
= GND
T
A
= +25°C
T
A
= +85°C
0.75
-0.25
-0.75
-1.5
-2.75
+0.75
0
-0.75
-2.25
-2.25
+2.25
+1.5
+0.50
-1.0
mA
CONDITIONS
MIN
2.6
2.20
2.35
16
27
0.1
0.1
V
IN
+1.75
+0.75
0
-1.25
%
TYP
MAX
5.5
2.55
25
42
1
UNITS
V
V
µA
µA
V
OUT Bias Current
For preset output voltages
FB Threshold Accuracy
2
_______________________________________________________________________________________
16µA I
Q
, 1.2A PWM DC-DC
Step-Down Converters
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= V
INP
= V
SHDN
= 3.6V, T
A
= -40°C to +85°C. Typical values are at T
A
= +25°C, unless otherwise noted.) (Note 2)
PARAMETER
MAX1556,
D1 = IN, D2 = GND;
MAX1556A
D1 = D2 = IN
MAX1557,
D1 = IN, D2 = GND
MAX1556/MAX1556A
p-Channel On-Resistance
MAX1557
n-Channel On-Resistance
p-Channel Current-Limit
Threshold
n-Channel Zero Crossing
Threshold
RMS LX Output Current
LX Leakage Current
Maximum Duty Cycle
Minimum Duty Cycle
Internal Oscillator Frequency
SS Output Impedance
SS Discharge Resistance
Thermal-Shutdown Threshold
Thermal-Shutdown Hysteresis
LOGIC INPUTS (D1, D2,
SHDN)
Input-Voltage High
Input-Voltage Low
Input Leakage
T
A
= +25°C
T
A
= +85°C
0.1
0.1
2.6V
≤
V
IN
≤
5.5V
1.4
0.4
1
V
V
µA
∆V
SS
/ I
SS
for I
SS
= 2µA
SHDN
= GND, 1mA sink current
0.9
130
1
200
90
+160
15
MAX1556/MAX1556A
MAX1557
V
IN
= 5.5V, LX =
GND or IN
T
A
= +25°C
T
A
= +85°C
100
0
1.1
300
200
0.1
0.1
V
IN
= 3.6V
V
IN
= 2.6V
MAX1556/MAX1556A
MAX1557
1.5
0.8
20
CONDITIONS
V
IN
= 2.6V to 3.6V
V
IN
= 3.6V to 5.5V
V
IN
= 2.6V to 3.6V
V
IN
= 3.6V to 5.5V
V
IN
= 3.6V
V
IN
= 2.6V
V
IN
= 3.6V
V
IN
= 2.6V
MIN
TYP
-0.37
0.33
-0.1
0.09
0.19
0.23
0.35
0.42
0.27
0.33
1.8
1.0
35
2.1
1.2
45
1.8
1.0
10
0.48
Ω
A
mA
A
RMS
µA
%
%
MHz
kΩ
Ω
°C
°C
0.7
0.35
Ω
MAX
UNITS
MAX1556/MAX1556A/MAX1557
Line Regulation
%
Note 2:
All units are 100% production tested at T
A
= +25°C. Limits over the operating range are guaranteed by design.
Note 3:
For the MAX1556, 3.3V output accuracy is specified with a 4.2V input.
_______________________________________________________________________________________
3
16µA I
Q
, 1.2A PWM DC-DC
Step-Down Converters
MAX1556/MAX1556A/MAX1557
Typical Operating Characteristics
(V
IN
= V
INP
= 3.6V, D1 = D2 =
SHDN
= IN, Circuits of Figures 2 and 3, T
A
= +25°C, unless otherwise noted.)
EFFICIENCY vs. LOAD CURRENT
WITH 3.3V OUTPUT
MAX1556/7 toc01
EFFICIENCY vs. LOAD CURRENT
WITH 2.5V OUTPUT
MAX1556/7 toc02
EFFICIENCY vs. LOAD CURRENT
WITH 1.8V OUTPUT
MAX1556/7 toc03
100
90
V
IN
= 4.2V
EFFICIENCY (%)
80
70
60
50
40
0.1
1
10
100
1000
V
IN
= 3.6V
V
IN
= 5V
100
90
EFFICIENCY (%)
80
70
60
50
40
V
IN
= 5V
V
IN
= 3.6V
V
IN
= 3V
V
IN
= 2.6V
100
90
EFFICIENCY (%)
80
V
IN
= 2.6V
70
60
50
40
V
IN
= 5V
V
IN
= 3.6V
V
IN
= 3V
10,000
0.1
1
10
100
1000
10,000
0.1
1
10
100
1000
10,000
LOAD CURRENT (mA)
LOAD CURRENT (mA)
LOAD CURRENT (mA)
EFFICIENCY vs. LOAD CURRENT
WITH 1.0V OUTPUT (MAX1557)
MAX1556/7 toc04
OUTPUT VOLTAGE
vs. LOAD CURRENT
MAX1556/7 toc05
OUTPUT VOLTAGE vs. INPUT VOLTAGE
WITH 600mA LOAD
1.788
1.787
OUTPUT VOLTAGE (V)
1.786
1.785
1.784
1.783
1.782
1.781
1.780
1.779
T
A
= +85°C
T
A
= +25°C
T
A
= -40°C
MAX1556/7 toc06
100
90
EFFICIENCY (%)
80
V
IN
= 3.6V
70
60
50
40
0.1
1
10
100
V
IN
= 3V
V
IN
= 2.6V
V
IN
= 5V
1.84
1.83
1.82
OUTPUT VOLTAGE (V)
1.81
1.80
1.79
1.78
1.77
1.76
1.75
1.74
T
A
= +85°C
T
A
= +25°C
T
A
= -45°C
1.789
1000
0
200
400
600
800
1000
1200
2.5
3.0
3.5
4.0
4.5
5.0
5.5
LOAD CURRENT (mA)
LOAD CURRENT (mA)
INPUT VOLTAGE (V)
OUTPUT VOLTAGE vs. INPUT VOLTAGE
WITH NO LOAD
MAX1556/7 toc07
SUPPLY CURRENT vs. INPUT VOLTAGE
MAX1556/7 toc08
HEAVY-LOAD SWITCHING WAVEFORMS
MAX1556/7 toc09
1.812
1.811
1.810
OUTPUT VOLTAGE (V)
1.809
1.808
1.807
1.806
1.805
1.804
1.803
2.5
3.0
3.5
4.0
4.5
5.0
T
A
= +85°C
T
A
= -40°C
T
A
= +25°C
20
18
16
SUPPLY CURRENT (µA)
14
12
10
8
6
4
2
0
I
LOAD
= 750mA
V
OUT
AC-COUPLED
10mV/div
V
LX
2V/div
0
I
LX
500mA/div
0
1
2
3
4
5
6
400ns
INPUT VOLTAGE (V)
5.5
INPUT VOLTAGE (V)
4
_______________________________________________________________________________________
16µA I
Q
, 1.2A PWM DC-DC
Step-Down Converters
Typical Operating Characteristics (continued)
(V
IN
= V
INP
= 3.6V, D1 = D2 =
SHDN
= IN, Circuits of Figures 2 and 3, T
A
= +25°C, unless otherwise noted.)
EXTERNAL FEEDBACK
SWITCHING WAVEFORMS
MAX1556/7 toc10b
MAX1556/MAX1556A/MAX1557
LIGHT-LOAD SWITCHING WAVEFORMS
MAX1556/7 toc10
SOFT-START/SHUTDOWN WAVEFORMS
MAX1556/7 toc11
V
OUT
20mV/div
AC-COUPLED
V
LX
2V/div
0
V
SHDN
V
OUT
5V/div
0
1V/div
0
C
SS
= 470pF
R
LOAD
= 4Ω
V
LX
2V/div
0
200mA/div
I
LX
V
IN
= 5V, V
OUT
= 3.3V, I
OUT
= 500mA
4µs/div
2µs/div
I
LX
200mA/div
0
I
IN
100µs/div
500mA/div
0
I
LX
0
500mA/div
0
SOFT-START RAMP TIME vs. C
SS
MAX1556/7 toc12
LOAD TRANSIENT
MAX1556/7 toc13
10
SOFT-START RAMP TIME (ms)
V
OUT
50mV/div
AC-COUPLED
1
500mA/div
I
OUT
I
OUTMIN
= 20mA
0
0.1
0
500
1000
1500
2000
2500
20µs/div
C
SS
(pF)
LOAD TRANSIENT
MAX1556/7 toc14
LINE TRANSIENT
MAX1556/7 toc15
BODE PLOT
40
4V
30
20
10
GAIN (dB)
0
-10
-20
-30
-40
-50
0
-60
0.1
C
OUT
= 22µF, R
LOAD
= 4Ω
1
10
FREQUENCY (kHz)
100
0dB
PHASE MARGIN = 53°
MAX1556/7 toc16
240
210
180
PHASE (DEGREES)
150
120
90
60
30
0
-30
V
OUT
V
IN
50mV/div
AC-COUPLED
3.5V
V
OUT
500mA/div
0
I
OUT
I
OUTMIN
= 180mA
20µs/div
40µs/div
I
LX
10mV/div
AC-COUPLED
200mA/div
-60
1000
_______________________________________________________________________________________
5
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