Maxim MAX8556 4a ultra-low-input-voltage ldo regulator Datasheet

19-3257; Rev 2; 8/09
KIT
ATION
EVALU
E
L
B
AVAILA
4A Ultra-Low-Input-Voltage
LDO Regulators
The MAX8556/MAX8557 low-dropout linear regulators
operate from input voltages as low as 1.425V and are
able to deliver up to 4A of continuous output current
with a typical dropout voltage of only 100mV. The output voltage is adjustable from 0.5V to VIN - 0.2V.
Designed with an internal p-channel MOSFET pass transistor, the MAX8556/MAX8557 maintain a low 800µA typical supply current, independent of the load current and
dropout voltage. Using a p-channel MOSFET eliminates
the need for an additional external supply or a noisy internal charge pump. Other features include a logic-controlled shutdown mode, built-in soft-start, short-circuit
protection with foldback current limit, and thermal-overload protection. The MAX8556 features a POK output that
transitions high when the regulator output is within ±10%
of its nominal output voltage. The MAX8557 offers a
power-on reset output that transitions high 140ms after the
output has achieved 90% of its nominal output voltage.
Features
o 1.425V to 3.6V Input Voltage Range
o Guaranteed 4A Output Current
o ±1% Output Accuracy Over Load/Line/
Temperature
o 100mV Dropout at 4A Load (typ)
o Built-In Soft-Start
o 800µA (typ) Operating Supply Current
o 150µA (max) Shutdown Supply Current
o Short-Circuit Current Foldback Protection
o Thermal-Overload Protection
o ±10% Power-OK (MAX8556)
o 140ms Power-On Reset Output (MAX8557)
o Fast Transient Response
o 16-Pin Thin QFN (5mm x 5mm) Package
The MAX8556/MAX8557 are available in a 16-pin thin
QFN 5mm x 5mm package with exposed paddle.
Applications
Ordering Information
TEMP
RANGE
PART
Servers and Storage Devices
Base Stations
-40°C to +85°C 16 Thin QFN-EP*
POK
POK
-40°C to +85°C 16 Thin QFN-EP*
POR
MAX8557ETE+
Optical Modules
FEATURE
MAX8556ETE/V+ -40°C to +85°C 16 Thin QFN-EP*
MAX8556ETE+
Networking
PINPACKAGE
+Denotes a lead(Pb)-free/RoHS-compliant package.
/V Denotes an automotive qualified part.
*EP = Exposed pad.
Point-of-Load Supplies
ATE
Pin Configuration
GND
N.C.
13
14
N.C.
15
EN
16
+
OUT
OUT
11
10
9
MAX8556
(MAX8557)
EP
1
2
3
4
IN
POK
(POR)
FB
GND
12
IN
MAX8556
(MAX8557)
EN
FB
OUT
OUT
IN
IN
VOUT
0.5V TO VIN - 0.2V
VIN
1.425V TO 3.6V
IN
TOP VIEW
POK (POR)
Typical Operating Circuit
8
OUT
7
OUT
6
IN
5
IN
THIN QFN
5mm x 5mm
________________________________________________________________ Maxim Integrated Products
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.
1
MAX8556/MAX8557
General Description
MAX8556/MAX8557
4A Ultra-Low-Input-Voltage
LDO Regulators
ABSOLUTE MAXIMUM RATINGS
IN, EN, POK, POR to GND .......................................-0.3V to +4V
FB, OUT to GND ..........................................-0.3V to (VIN + 0.3V)
Output Short-Circuit Duration.....................................Continuous
Continuous Power Dissipation (TA = +70°C)
16-Pin Thin QFN (derate 33.3mW/°C
above +70°C) (Note 1)............................................2666.7mW
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
Note 1: Maximum power dissipation is obtained using JEDEC JESD51-5 and JESD51-7 standards.
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
(VEN = VIN = 1.8V, VOUT = 1.5V, IOUT = 2mA, TA = -40°C to +85°C, typical values are at TA = +25°C, unless otherwise noted.) (Note 2)
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
3.600
V
IN
Input Voltage Range
Input Undervoltage Lockout
1.425
VIN rising, 70mV hysteresis
1.30
1.35
1.40
VIN falling
1.23
1.28
1.33
V
OUT
Output Voltage Range
0.5
Load Regulation
IOUT = 2mA to 4A
Line Regulation
VIN = 1.425V to 3.6V, VOUT = 1.225V
Dropout Voltage
VIN = 1.425V, IOUT = 4A, VFB = 480mV
Regulated Output-Voltage Current
Limit
VIN = 3.6V, VOUT = 3V, VFB = 460mV
5
Load Capacitance
ESR < 50mA
16
FB Threshold Accuracy
(Note 3)
VOUT = 1.225V to 3V, VIN = VOUT + 0.2V to 3.6V,
IOUT = 2mA to 4A
495
FB Input Bias Current
VFB = 0.5V, VIN = 3.6V
3.4
0.1
-0.15
V
%/A
0
+0.15
%/V
100
200
mV
7
9
A
120
µF
500
505
mV
0.001
1
µA
VIN = 1.425V to 3.6V, VOUT = 1.225V
800
1600
Dropout, VIN = 3.6V, VFB = 480mV
1000
2000
FB
GND
GND Supply Current
GND Shutdown Current
VIN = 3.6V, EN = GND
150
µA
µA
POK
FB Power-OK Fault Threshold
FB moving out of regulation,
VIN = 1.425V to 3.6V, 10mV hysteresis
POK Output Voltage, Low
VFB = 0.4V or 0.6V, IPOK = 2mA
2
FB high
540
550
560
FB low
440
450
460
25
200
_______________________________________________________________________________________
mV
mV
4A Ultra-Low-Input-Voltage
LDO Regulators
(VEN = VIN = 1.8V, VOUT = 1.5V, IOUT = 2mA, TA = -40°C to +85°C, typical values are at TA = +25°C, unless otherwise noted.) (Note 2)
PARAMETER
CONDITIONS
POK Output Current, High
VPOK = 3.6V VFB = 0.5
POK Delay Time
From FB rising to POK high
MIN
25
TYP
MAX
UNITS
0.001
1
µA
50
100
µs
EN
Enable Input Threshold
VIN = 1.425V to 3.6V
Enable Input Bias Current
VEN = 0V or 3.6V
EN rising
1.25
EN falling
V
0.4
-1
+1
µA
THERMAL SHUTDOWN
Thermal-Shutdown Threshold
Output on and off
TJ rising
+160
TJ falling
+115
°C
POR
FB Power-On Reset Fault Threshold
FB falling, VIN = 1.425V to 3.6V, 10mV hysteresis
POR Output Voltage, Low
POR Output Current, High
POR Rising Delay Time
FB rising to POR high impedance
440
450
460
mV
VFB = 0.4V, IPOR = 2mA
25
200
mV
VPOR = 3.6V, VFB = 0.5V
0.001
1
µA
140
200
ms
100
SOFT-START
Soft-Start Time
100
µs
Note 2: Specifications to TA = -40°C are guaranteed by design and not production tested.
Note 3: Minimum supply voltage for output accuracy must be at least 1.425V.
Typical Operating Characteristics
(VEN = VIN = +1.8V, VOUT = +1.5V, IOUT = 4A, COUT = 20µF, CIN = 20µF, and TA = +25°C, unless otherwise noted.)
1.45
1.40
1.35
MAX8556 toc02
TA = +25°C
1.5015
1.5010
1.5005
TA = +85°C
1.5000
1.4995
1.4990
TA = -40°C
1.4980
ILOAD = 2A
1.8
2.4
INPUT VOLTAGE (V)
3.0
3.6
800
ILOAD = 2A
700
600
500
ILOAD = 0A
400
300
100
0
1.4975
1.2
ILOAD = 4A
900
200
1.4985
1.30
1000
GND CURRENT (µA)
TA = -25°C
TA = -40°C
1.5020
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
1.50
MAX8556 toc01
TA = -85°C
GND CURRENT vs. INPUT VOLTAGE
OUTPUT VOLTAGE vs. LOAD CURRENT
1.5025
MAX8556 toc03
OUTPUT VOLTAGE vs. INPUT VOLTAGE
1.55
0
1
2
LOAD CURRENT (A)
3
4
0
1.2
2.4
3.6
INPUT VOLTAGE (V)
_______________________________________________________________________________________
3
MAX8556/MAX8557
ELECTRICAL CHARACTERISTICS (continued)
Typical Operating Characteristics (continued)
(VEN = VIN = +1.8V, VOUT = +1.5V, IOUT = 4A, COUT = 20µF, CIN = 20µF, and TA = +25°C, unless otherwise noted.)
DROPOUT VOLTAGE vs. LOAD CURRENT
GND CURRENT vs. TEMPERATURE
700
ILOAD = 2A
600
500
400
80
DROPOUT VOLTAGE (mV)
800
ILOAD = 0A
300
70
30
10
0
0
35
60
VIN
40
100
10
2.5V
50
20
-15
MAX8556 toc06
1.8V
60
200
-40
LINE-TRANSIENT RESPONSE
MAX8556 toc05
90
MAX8556 toc04
900
GND CURRENT (µA)
MAX8556/MAX8557
4A Ultra-Low-Input-Voltage
LDO Regulators
VOUT
(AC-COUPLED)
VIN = 1.5V
0
85
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
100µs/div
LOAD CURRENT (A)
TEMPERATURE (°C)
4A LOAD-TRANSIENT RESPONSE
2A LOAD-TRANSIENT RESPONSE
MAX8556 toc07
VOUT
(AC-COUPLED)
MAX8556 toc08
50mV/div
IOUT
2A/div
VOUT
(AC-COUPLED)
50mV/div
IOUT
40µs/div
1A/div
40µs/div
ENABLE WAVEFORMS
SHORT-CIRCUIT WAVEFORMS
MAX8556 toc09
MAX8556 toc10
VIN
3.6V
2V/div
VOUT
1V/div
IOUT
5A/div
2V/div
VEN
1V/div
VOUT
100µs/div
4
10mV/div
200µs/div
_______________________________________________________________________________________
4A Ultra-Low-Input-Voltage
LDO Regulators
PSRR vs. FREQUENCY
STARTUP WAVEFORMS
MAX8556 toc12
MAX8556 toc11
90
80
70
2V/div
PSRR (dB)
60
VIN
2A/div
50
40
IIN
30
1V/div
20
VOUT
VIN = 2.5V
ILOAD = 1A
10
0
1
10
1000
100
100µs/div
FREQUENCY (kHz)
EXPOSED PADDLE TEMPERATURE
vs. AMBIENT TEMPERATURE
FB REGULATION vs. TEMPERATURE
90
80
MAX8556 toc14
0.510
MAX8556 toc13
0.505
70
FB (V)
60
50
0.500
40
30
0.495
20
DATA TAKEN USING
MAX8556 EVALUATION KIT
10
ILOAD = 50mA
0.490
0
0
17
34
51
68
-40
85
-15
10
35
60
AMBIENT TEMPERATURE (°C)
TEMPERATURE (°C)
FOLDBACK CURRENT-LIMIT WAVEFORMS
CURRENT-LIMIT THRESHOLD
vs. TEMPERATURE
MAX8556 toc15
7.8
VOUT
500mV/div
IOUT
5A/div
85
MAX8556 toc16
8.0
CURRENT-LIMIT THRESHOLD (A)
EXPOSED PADDLE TEMPERATURE (°C)
100
7.6
7.4
7.2
7.0
6.8
6.6
6.4
6.2
6.0
100µs/div
-40
-15
10
35
60
85
TEMPERATURE (°C)
_______________________________________________________________________________________
5
MAX8556/MAX8557
Typical Operating Characteristics (continued)
(VEN = VIN = +1.8V, VOUT = +1.5V, IOUT = 4A, COUT = 20µF, CIN = 20µF, and TA = +25°C, unless otherwise noted.)
4A Ultra-Low-Input-Voltage
LDO Regulators
MAX8556/MAX8557
Pin Description
PIN
NAME
FUNCTION
1–6
IN
LDO Input. Connect to a 1.425V to 3.6V input voltage. Bypass with a 22µF ceramic capacitor to GND.
7–11
OUT
LDO Output. Bypass with 2 x 10µF ceramic capacitors to GND. A smaller capacitance can be used if
the maximum load current is less than 4A.
POK
(MAX8556)
Power-OK Output. Open-drain output that pulls low when VOUT is outside ±10% of the expected
regulation voltage or when EN is low. POK is high impedance when VOUT is within ±10% of the
nominal output voltage. Connect a resistor from POK to a logic supply of less than 3.6V.
POR
(MAX8557)
Power-On Reset. Open-drain output goes high impedance 140ms after the output is above 90% of its
nominal regulation voltage. POR pulls low immediately after an output fault or when EN is low.
Connect a resistor from POR to a logic supply of less than 3.6V.
12
Feedback Input. VFB is regulated to 0.5V. Connect to the center tap of a resistor-divider from output
to GND to set the desired output voltage.
13
FB
14
GND
Ground
15
N.C.
Connect to GND or Leave Unconnected
16
EN
Enable Input. Connect to GND or a logic low to shut down the device. Connect to IN or a logic high
for normal operation.
—
EP
Exposed Paddle. Connect to GND and to a ground plane for heatsinking.
Block Diagram
IN
THRESHOLD
THERMALOVERLOAD
PROTECTION
0.50V
REF
UNDERVOLTAGE
LOCKOUT
ERROR
AMP
P
0.45V
0.55V
EN
SHUTDOWN
LOGIC
CURRENTLIMIT
COMPARATOR
OUT
FB
POK
(POR)
MAX8556
(MAX8557)
POK (POR)
CIRCUITRY
GND
6
_______________________________________________________________________________________
N
4A Ultra-Low-Input-Voltage
LDO Regulators
The MAX8556/MAX8557 low-dropout linear regulators
are capable of delivering up to 4A from low-input voltage supplies ranging from 1.425V to 3.6V with only
200mV of dropout (max). The pMOS output stage can
be driven from input voltages down to 1.425V without
sacrificing stability or transient performance. Supply
current is not a significant function of load or input headroom because this regulator has a pMOS output device.
The MAX8556/MAX8557 are fully protected from an output short circuit by current-limiting and thermal-overload
circuitry. The low-power shutdown mode reduces supply current to 0.2µA (typ) to maximize battery life in
portable applications. The MAX8556 includes an opendrain power-OK signal (POK) that goes high when the
regulator output is within ±10% of its nominal output
voltage. The MAX8557 includes an open-drain poweron-reset output (POR) that goes high 140ms after the
output has risen above 90% of its nominal value.
Shutdown Mode
The MAX8556/MAX8557 feature a low-power shutdown
mode that reduces quiescent current to 0.2µA (typ).
Drive EN low to disable the voltage reference, error
amplifier, gate-drive circuitry, and pass transistor, and
pull the output low with 5kΩ impedance. Drive EN high
or connect to IN for normal operation.
Power-OK Output (POK, MAX8556 Only)
The MAX8556 features a power-OK (POK) output to
indicate the status of the output. POK is high impedance
when the regulator output is within ±10% of its nominal
output voltage. If the output voltage falls/rises outside
this range or the IC experiences thermal fault, POK is
internally pulled low. This open-drain output requires an
external pullup resistor to VIN or another logic supply
below 3.6V. For glitch immunity, an internal delay circuit
prevents the output from switching for 50µs (typ) after
the trip threshold is initially reached. POK is low when
the IC is in shutdown mode.
Internal p-Channel Pass Transistor
Power-On Reset (POR, MAX8557 Only)
The MAX8556/MAX8557 feature a 25mΩ p-channel
MOSFET pass transistor. Unlike similar designs using
pnp pass transistors, p-channel MOSFETs require no
base drive, which reduces quiescent current; pnpbased regulators also waste considerable current in
dropout when the pass transistor saturates, and use
high base-drive currents under large loads. The
MAX8556/MAX8557 do not suffer from these problems
and consume only 800µA (typ) of quiescent current
under heavy loads, as well as in dropout.
The MAX8557 features a power-on reset output that
goes high impedance 140ms (typ) after the output
reaches 90% of its nominal value. This open-drain output requires an external pullup resistor to VIN or another
logic supply less than 3.6V. When the output falls below
90% of the nominal output voltage or the IC experiences a thermal fault, POR immediately transitions low.
POR is low when the IC is in shutdown mode.
Short-Circuit/Thermal Fault Protection
The MAX8556/MAX8557 are fully protected from output
short circuits through current-limiting and thermal-overload circuitry. When the output is shorted to ground, the
output current is foldback limited to 3A (max). Under
these conditions, the device quickly heats up. When
the junction temperature reaches +160°C, the thermaloverload circuitry turns off the output, allowing the
device to cool. When the junction cools to +115°C, the
output turns back on and attempts to establish regulation. Current limiting and thermal protection continue
until the fault is removed.
Operating Region and Power Dissipation
The maximum power dissipation depends on the thermal resistance of the IC package and the circuit board,
the temperature difference between the die junction and
ambient air, and the rate of ambient airflow. The power
dissipated by the IC is P = IOUT x (VIN - VOUT). Proper
PCB layout can increase the allowed power dissipation
by dissipating heat in the board instead of the package.
See the Thermal Considerations in PCB Layout section
for more details.
_______________________________________________________________________________________
7
MAX8556/MAX8557
Detailed Description
MAX8556/MAX8557
4A Ultra-Low-Input-Voltage
LDO Regulators
Applications Information
Output Voltage Selection
The MAX8556/MAX8557 feature an adjustable output
voltage from 0.5V to 3.4V. Set the output voltage using
an external resistor-divider from the output to GND with
FB connected to the center tap as shown in Figures 1
and 2. Choose R3 ≤ 1kΩ for light-load stability.
Determine R2 using the following equation:
⎛V
⎞
R2 = R 3 x ⎜ OUT − 1⎟
⎝ VFB
⎠
VIN
1.425V TO 3.6V
C1
2 x 10µF
1–6
U1
R1
100kΩ
Capacitors are required at the MAX8556/MAX8557
inputs and outputs for stable operation over the full
temperature range and with load currents up to 4A.
Connect 2 x 10µF capacitors between IN and GND and
2 x 10µF low equivalent-series-resistance (ESR) capacitors between OUT and GND. The input capacitor (CIN)
lowers the source impedance of the input supply. If the
MAX8556/MAX8557s’ input is close to the output of the
source supply, a smaller input capacitance can be
used. Otherwise, 2 x 10µF ceramic input capacitors are
recommended. The output capacitor’s (C OUT ) ESR
affects output noise and may affect output stability. Use
output capacitors with an ESR of 0.05Ω or less to
ensure stability and optimum transient dropout. For
good output transient performance, use the following
formula to select a minimum output capacitance:
COUT = IOUT(MAX) x 1µF/200mA
R2
1.4kΩ
MAX8556
12
POK
POK
FB
C2
2 x 10µF
13
R3
1kΩ
ENABLED
18
SHUTDOWN
EN
GND
14
N.C.
where VOUT is the desired output voltage and VFB is 0.5V.
Capacitor Selection and
Regulator Stability
OUT
IN
VOUT
1.2V AT 4A
7–11
15
Figure 1. MAX8556 Typical Application Circuit
VIN
1.7V TO 3.6V
C1
2 x 10µF
1–6
OUT
IN
U2
R1
100kΩ
R2
2kΩ
MAX8557
12
POR
POR
FB
C2
2 x 10µF
13
R3
1kΩ
ENABLED
18
SHUTDOWN
VOUT
1.5V AT 4A
7–11
EN
GND
14
N.C.
15
Noise, PSRR, and Transient Response
The MAX8556/MAX8557 are designed to operate with
low-dropout voltages and low quiescent currents while
still maintaining low noise, good transient response,
and high AC rejection (see the Typical Operating
Characteristics for a plot of Power-Supply Rejection
Ratio (PSRR) vs. Frequency). When operating from
noisy sources, improved supply-noise rejection and
transient response can be achieved by increasing the
values of the input and output bypass capacitors and
through passive filtering techniques. The MAX8556/
MAX8557 load-transient response graphs (see the
8
Figure 2. MAX8557 Typical Application Circuit
Typical Operating Characteristics) show two components of the output response: a DC shift from the output
impedance due to the load current change, and the
transient response. A typical transient overshoot for a
step change in the load current from 40mA to 4A is
40mV. Use an output capacitance from 20µF to 120µF
to attenuate the overshoot.
_______________________________________________________________________________________
4A Ultra-Low-Input-Voltage
LDO Regulators
How much power the package can dissipate strongly
depends on the mounting method of the IC to the PCB
and the copper area for cooling. Using the JEDEC test
standard, the maximum power dissipation allowed in
the package is 2667mW. This data is obtained with
+70°C ambient temperature and +150°C maximum
junction temperature. The test board has dimensions of
3in x 3in with four layers of 2oz copper and FR-4 material with 62mil finished thickness. Nine thermal vias are
used under the thermal paddle with a diameter of 12mil
and 1mil plated copper thickness. Top and bottom layers are used to route the traces. Two middle layers are
solid copper and isolated from the nine thermal vias.
More power dissipation can be handled by the package if great attention is given during PCB layout. For
example, using the top and bottom copper as a
heatsink and connecting the thermal vias to one of the
middle layers (GND) transfers the heat from the package into the board more efficiently, resulting in lower
junction temperature at high power dissipation in some
MAX8556/MAX8557 applications. Furthermore, the solder mask around the IC area on both top and bottom
layers can be removed to radiate the heat directly into
the air. The maximum allowable power dissipation in
the IC is as follows:
PMAX =
where TJ(MAX) is the maximum junction temperature
(+150°C), T A is the ambient air temperature, θ JC
(1.7°C/W for the 16-pin TQFN) is the thermal resistance
from the junction to the case, and θCA is the thermal
resistance from the case to the surrounding air through
the PCB, copper traces, and the package materials.
θCA is directly related to system level variables and can
be modified to increase the maximum power dissipation. The TQFN package has an exposed thermal pad
on its underside. This pad provides a low thermal resistance path for heat transfer into the PCB. This low thermally resistive path carries a majority of the heat away
from the IC. The PCB is effectively a heatsink for the IC.
The exposed paddle should be connected to a large
ground plane for proper thermal and electrical performance. The minimum size of the ground plane is
dependent upon many system variables. To create an
efficient path, the exposed paddle should be soldered
to a thermal landing, which is connected to the ground
plane by thermal vias. The thermal landing should be at
least as large as the exposed paddle and can be made
larger depending on the amount of free space from the
exposed paddle to the other pin landings.
A sample layout is available on the MAX8556 evaluation kit to speed designs.
(TJ(MAX) − TA )
θJC + θCA
Chip Information
TRANSISTOR COUNT: 3137
PROCESS: BiCMOS
Package Information
For the latest package outline information and land patterns, go
to www.maxim-ic.com/packages. Note that a “+”, “#”, or “-” in
the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status.
PACKAGE TYPE
PACKAGE CODE
DOCUMENT NO.
16 TQFN-EP
T1655+2
21-0140
_______________________________________________________________________________________
9
MAX8556/MAX8557
Thermal Considerations
in PCB Layout
MAX8556/MAX8557
4A Ultra-Low-Input-Voltage
LDO Regulators
Revision History
REVISION
NUMBER
REVISION
DATE
0
4/04
Initial release
—
1
8/08
Revised Pin Configuration.
1
2
8/09
Added automotive version of the MAX8556.
1
DESCRIPTION
PAGES
CHANGED
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implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
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