MAX1534ETE [MAXIM]
High-Efficiency, Triple-Output, Keep-Alive Power Supply for Notebook Computers; 高效率，三路输出，不间断电源，用于笔记本电脑
| 型号： | MAX1534ETE |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | High-Efficiency, Triple-Output, Keep-Alive Power Supply for Notebook Computers |
| 文件： | 总16页 (文件大小：398K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
19-2662; Rev 0; 10/02
High-Efficiency, Triple-Output, Keep-Alive
Power Supply for Notebook Computers
General Description
Features
The MAX1534 is a high-efficiency, triple-output power
supply for keep-alive (always on) voltage rails. The
500mA buck regulator with an internal current-limited
0.5Ω PMOS steps down the battery or wall adapter
supply rail to a fixed 5V or an adjustable output voltage.
Two integrated low-voltage linear regulators follow this
output and provide two independent preset output volt-
ages of 3.3V and 1.8V, or adjustable output voltages.
ꢀ One Switching and Two Linear Regulators
ꢀ Switching Regulator
+4.5V to +24V Input Voltage Range
Over 95% Efficiency
Up to 500mA Output Current
Up to 200kHz Switching Frequency
Fixed 5V or Adjustable Output Voltage
Internal 0.5Ω PMOS Switch
100% Maximum Duty Cycle for Low-Dropout
Operation
The buck regulator utilizes a peak current-limit, pulse-
frequency modulation (PFM) architecture for highest
light-load efficiency to conserve battery life. High
switching frequencies (up to 200kHz) allow the use of
tiny surface-mount inductors and output capacitors.
Operation to 100% duty cycle minimizes dropout volt-
age (250mV at 500mA).
ꢀ Two Low-Dropout Linear Regulators
Up to 160mA Output Current (Each)
3.3V/Adj Output Voltage for OUT1
1.8V/Adj Output Voltage for OUT2
The low-dropout linear regulators use an internal
P-channel metal-oxide (PMOS) pass transistor to mini-
mize supply current and deliver up to 160mA each of
continuous current.
ꢀ
ꢀ
1.5% Accurate Output Voltage
4% Accurate Shutdown for Low ꢀattery
Detection
The MAX1534 includes a power-OK (POK) signal that
indicates all outputs are in regulation. The 4% accurate
threshold of the SHDN input permits its use as a low-
battery detector.
ꢀ Thermal Shutdown Protection
ꢀ POK Output
ꢀ 1mW Typical Standby Power
The MAX1534 is available in a small 16-pin thin QFN
(4mm ✕ 4mm) package, occupying 33% less board
space than discrete solutions.
Applications
Ordering Information
Notebook and Sub-
Notebook Computers
Wake-On LAN
2 to 4 Li+ Cells Battery-
Powered Devices
Hand-Held Devices
Keep-Alive Supplies
Standby Supplies
PART
TEMP RANGE PIN-PACKAGE
MAX1534ETE
-40°C to +85°C 16 Thin QFN (4mm × 4mm)
Pin Configuration appears at end of data sheet.
Typical Operating Circuit
V
IN
= +7V TO +24V
IN
SHDN
POK
BP
FB3
LX
PRESET
ILIM
FB1
FB2
V
OUT3
= +5V ALWAYS
MAX1534
V
= +3.3V ALWAYS
= +1.8V ALWAYS
OUT1
OUT2
OUT1
LDOIN
V
OUT2
GND
________________________________________________________________ Maxim Integrated Products
1
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.
High-Efficiency, Triple-Output, Keep-Alive
Power Supply for Notebook Computers
AꢀSOLUTE MAXIMUM RATINGS
IN, ILIM, PRESET, SHDN to GND...........................-0.3V to +25V
FB1, FB2, FB3, LDOIN, BP to GND..........................-0.3V to +6V
Continuous Power Dissipation (T = +70°C)
A
16-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
OUT1, OUT2, POK to GND ...................-0.3V to (V
LX to GND.......................................................-2V to (V + 0.3V)
OUT1, OUT2 Short Circuit to GND.............................Continuous
Peak IN Current........................................................................2A
Maximum IN DC Current...................................................500mA
+ 0.3V)
LDOIN
IN
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
(Circuit of Figure 1, V = 12V, ILIM = GND, PRESET = GND, T = 0°C to +85°C, unless otherwise noted. Typical values are at T
=
IN
A
A
+25°C.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
24
UNITS
V
Input Voltage Range
Input Supply Current
V
4.5
IN
IN
I
No load, FB3 = 5.2V, LDOIN = GND
15
60
30
µA
Input Supply Current in
Dropout
I
No load, FB3 = V = 4.5V, LDOIN = GND
IN
110
µA
µA
V
IN(DROP)
Shutdown Supply Current
Input UVLO Threshold
BUCK REGULATOR
SHDN = GND
3.5
4.0
3.9
7
V
V
rising
falling
3.6
3.5
4.4
4.3
IN
IN
V
UVLO
T
T
T
T
= +25°C to +85°C
= 0°C to +85°C
4.92
4.90
5.00
5.00
1.00
1.00
3.5
5.08
5.10
1.015
1.02
6.25
0.62
A
A
A
A
FB3 Voltage Accuracy (Preset
Mode) (Note 1)
PRESET = GND
PRESET = IN
V
V
= +25°C to +85°C 0.985
FB3 Set Voltage (Adjustable
Mode) (Note 1)
V
FB3
= 0°C to +85°C
0.98
0.22
9
FB3 Bias Current
I
V
= 5.5V
µA
µs
µs
µs
FB3
FB3
LX Switch Minimum Off-Time
LX Switch Minimum On-Time
LX Switch Maximum On-Time
t
t
0.42
0.50
10
OFF(MIN)
t
ON(MIN)
ON(MAX)
11
1.0
V
V
= 6V
0.5
IN
IN
LX Switch On-Resistance
LX Current Limit
R
Ω
LX
= 4.5V
0.6
1.2
ILIM = IN
800
425
-75
1000
500
1200
575
+75
I
mA
LX(PEAK)
ILIM = GND
LX Zero-Crossing Threshold
LX Zero-Crossing Timeout
mV
µs
LX does not rise above threshold
30
T
T
= +25°C
1
A
A
V
= 24V, not
IN
LX Switch Leakage Current
µA
switching
= 0°C to +85°C
10
Dropout Voltage
V
I
= 500mA
250
0.1
0.9
mV
%/V
%
OUT3(DROPOUT) LX(DC)
Line Regulation
V
= 8V to 24V, I
= 200mA
IN
LX(DC)
Load Regulation
I
= 80mA to 400mA
LX(DC)
LINEAR REGULATORS
LDOIN Input Voltage
LDOIN Undervoltage Lockout
V
2.5
5.5
2.4
V
V
LDOIN
V
V
rising, hysteresis = 40mV typ
2.15
UVLO(LDO)
LDOIN
2
_______________________________________________________________________________________
High-Efficiency, Triple-Output, Keep-Alive
Power Supply for Notebook Computers
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, V = 12V, ILIM = GND, PRESET = GND, T = 0°C to +85°C, unless otherwise noted. Typical values are at T =
IN
A
A
+25°C.)
PARAMETER
SYMBOL
CONDITIONS
= 100µA to
MIN
TYP
MAX
UNITS
OUT1 Voltage Accuracy
(Preset Mode)
I
OUT1
V
V
PRESET = GND
3.20
3.30
3.37
V
OUT1
OUT2
160mA
OUT2 Voltage Accuracy
(Preset Mode)
I
OUT2
160mA
= 100µA to
PRESET = GND
1.74
1.80
1.00
1.84
V
FB1, FB2 Set Voltage
(Adjustable Mode)
I
OUT_
160mA
= 100µA to
V
, V
FB1 FB2
PRESET = IN
PRESET = IN, V
PRESET = IN
Continuous
0.97
-25
1.02
+25
V
nA
V
FB1, FB2 Bias Current
= V
= 1.1V
FB2
FB1
OUT1, OUT2 Adjustable Output
Voltage Range
V
,
OUT1
1.0
V
LDOIN
V
OUT2
Maximum OUT1 Output Current
OUT1 Current Limit
I
I
160
160
160
160
mA
mA
mA
mA
µA
OUT1(MAX)
OUT2(MAX)
550
Maximum OUT2 Output Current
OUT2 Current Limit
Continuous
550
265
LDOIN Current
I
I
= I
= 0, V
= 5.5V
165
120
OUT1
OUT_
OUT2
LDOIN
LDO_ Dropout Voltage
= 80mA (Note 2)
240
mV
V
= (V + 0.4V) or
LDOIN
OUT_
LDO_ Line Regulation
FAULT DETECTION
POK Threshold
-0.2
-13
0
+0.2
%/V
+2.5V to +5.5V, I
= 1mA
OUT_
OUT1, OUT2, and FB3 rising edge,
1% hysteresis (Note 3)
-11
10
-9
%
POK Propagation Delay
POK Output Low Voltage
POK Leakage Current
Falling edge, 50mV overdrive
µs
V
I
= 1mA
0.4
1
SINK
High state, forced to 5.5V
µA
°C
Thermal Shutdown Threshold
INPUTS AND OUTPUTS
SHDN Input Trip Level
Input Leakage Current
Typical hysteresis = 15°C
+160
1.0
Rising trip level, 100mV hysteresis
0.96
-1
1.04
+1
V
µA
V
V
, V
, V
= 0 or 24V
SHDN PRESET ILIM
Low
0.5
PRESET, ILIM Logic Levels
High
2.2
V
_______________________________________________________________________________________
3
High-Efficiency, Triple-Output, Keep-Alive
Power Supply for Notebook Computers
ELECTRICAL CHARACTERISTICS
(Circuit of Figure 1, V = 12V, ILIM = GND, PRESET = GND, T = -40°C to +85°C, unless otherwise noted.) (Note 4)
IN
A
PARAMETER
SYMBOL
CONDITIONS
MIN
4.5
3.6
3.5
TYP
MAX
24
UNITS
Input Voltage Range
V
V
V
V
V
IN
IN
IN
IN
rising
falling
4.4
4.3
Input Undervoltage Lockout
Threshold
V
V
UVLO
BUCK REGULATOR
FB3 Voltage Accuracy (Preset
Mode)
PRESET = GND
PRESET = IN
4.85
0.97
5.15
1.03
V
V
FB3 Set Voltage (Adjustable
Mode)
V
FB3
LX Switch Minimum Off-Time
LX Switch Maximum On-Time
t
0.22
8
0.62
12
µs
µs
OFF(MIN)
t
ON(MAX)
V
V
= 6V
1.0
IN
IN
LX Switch On-Resistance
LX Current Limit
R
Ω
LX
= 4.5V
1.2
ILIM = IN
800
425
1200
575
I
mA
LX(PEAK)
ILIM = GND
LINEAR REGULATORS
LDOIN Input Voltage
LDOIN UVLO
V
2.5
5.5
V
V
LDOIN
V
V
rising, hysteresis = 40mV (typ)
2.15
2.40
UVLO(LDO)
LDOIN
OUT1 Voltage Accuracy (Preset
Mode)
I
= 100µA to
OUT1
V
V
PRESET = GND
PRESET = GND
PRESET = IN
3.20
1.74
0.97
1.0
3.40
1.86
1.03
V
V
V
V
OUT1
OUT2
160mA
OUT2 Voltage Accuracy (Preset
Mode)
I
OUT2
160mA
= 100µA to
FB1, FB2 Set Voltage (Adjustable
Mode)
I
OUT_
160mA
= 100µA to
V
, V
FB1 FB2
OUT1, OUT2 Adjustable Output
Voltage Range
V
,
OUT1
PRESET = IN
V
LDOIN
550
V
OUT2
Maximum OUT1 Output Current
OUT1 Current Limit
I
I
Continuous
160
160
160
160
mA
mA
mA
mA
mV
OUT1(MAX)
OUT2(MAX)
Maximum OUT2 Output Current
OUT2 Current Limit
Continuous
550
250
LDO_ Dropout Voltage
I
= 80mA (Note 2)
OUT_
V
= (V
+ 0.4V) or +2.5V
OUT_
LDOIN
LDO_ Line Regulation
FAULT DETECTION
POK Threshold
-0.2
-13
+0.2
%/V
to +5.5V, I
= 1mA
OUT_
OUT1, OUT2, and FB3 rising edge, 1%
hysteresis (Note 3)
-8
%
4
_______________________________________________________________________________________
High-Efficiency, Triple-Output, Keep-Alive
Power Supply for Notebook Computers
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, V = 12V, ILIM = GND, PRESET = GND, T = -40°C to +85°C, unless otherwise noted.) (Note 4)
IN
A
PARAMETER
SYMBOL
CONDITIONS
MIN
0.96
2.2
TYP
MAX
UNITS
INPUTS AND OUTPUTS
SHDN Input Trip Level
Rising trip level, 100mV hysteresis
1.04
0.5
V
V
V
Low
PRESET, ILIM Logic Levels
High
Note 1: The output voltage at light loads has a DC regulation level higher than the error comparator threshold by half the ripple volt-
age.
Note 2: The dropout voltage is defined as V
- V
when V
= V
. Specification only applies when V
≥
LDOIN
OUT_
LDOIN
OUT_(NOM)
OUT_
2.5V.
Note 3: OUT1, OUT2 DC set point, FB3 set point at the DC trip threshold of buck regulator.
Note 4: Specifications to -40°C are guaranteed by design, not production tested.
Typical Operating Characteristics
(Circuit of Figure 1, V = +12V, PRESET = GND, T = +25°C, unless otherwise noted.)
IN
A
BUCK OUTPUT VOLTAGE
vs. LOAD CURRENT, CIRCUIT 1
BUCK EFFICIENCY
vs. LOAD CURRENT, CIRCUIT 1
BUCK EFFICIENCY
vs. LOAD CURRENT, CIRCUIT 2
100
100
95
90
85
80
75
70
65
60
55
50
5.20
5.15
5.10
5.05
5.00
4.95
4.90
4.85
4.80
V
= 6V
IN
V
= 7V
IN
95
90
85
80
75
70
65
60
V
= 12V
IN
V
= 12V
IN
V
= 12V
IN
V
= 20V
V
= 20V
IN
IN
V
= 20V
IN
V
= 6V
IN
55
(t LIMITED)
ON
ILIM = IN
ILIM = GND
ILIM = IN
1000
50
0
50 100 150 200 250 300 350 400 450 500
(mA)
0.1
1
10
(mA)
100
0.1
1
10
(mA)
100
1000
I
I
I
OUT3
OUT3
OUT3
SWITCHING FREQUENCY
vs. V , CIRCUIT 1, ILIM = IN
BUCK EFFICIENCY vs. LOAD CURRENT
CIRCUIT 1, V = 12V
IN
IN
200
180
160
140
120
100
80
89
87
85
83
I
= 500mA
L = 22µH
OUT3
L = 15µH
I
= 250mA
OUT3
81
79
77
75
I
= 100mA
OUT3
L = 10µH
60
I
= 50mA
OUT3
40
20
I
= 10mA
OUT3
ILIM = IN
0
6
10
14
18
22
26
0.1
1
10
(mA)
100
1000
V
(V)
IN
I
OUT3
_______________________________________________________________________________________
5
High-Efficiency, Triple-Output, Keep-Alive
Power Supply for Notebook Computers
Typical Operating Characteristics (continued)
(Circuit of Figure 1, V = +12V, PRESET = GND, T = +25°C, unless otherwise noted.)
IN
A
NO-LOAD SUPPLY CURRENT
SWITCHING FREQUENCY
vs. LOAD CURRENT, CIRCUIT 1, ILIM = IN
vs. V , CIRCUIT 1, ILIM = GND
IN
200
180
160
140
120
100
80
140
120
100
80
V
= 20V
IN
SHDN = IN
60
SHDN = IN
NOT CONNECTED
V
IN
= 12V
V
OUT3
60
40
TO V
LDOIN
SHDN = GND
40
V
= 7V
20
IN
20
0
0
6
10
14
18
22
26
0
50 100 150 200 250 300 350 400 450 500
(mA)
V
(V)
IN
I
OUT3
PEAK SWITCH CURRENT
vs. V , CIRCUIT 1, ILIM = IN
BUCK LOAD TRANSIENT
IN
MAX1534 toc09
1.4
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
V
OUT3
200mV/div
L = 10µH
AC-COUPLED
1A
0
I
LX
1A/div
L = 22µH
L = 15µH
V
10V
0
LX
10V/div
500mA
0
I
OUT3
500mA/div
I
= 300mA
22
OUT3
6
10
14
18
26
40µs/div
V
(V)
V
= 12V, I
= 100mA TO 450mA
OUT3
IN
IN
LINE TRANSIENT NEAR DROPOUT
LINE TRANSIENT
MAX1534 toc11
MAX1534 toc10
V
IN
5V/div
V
IN
5V/div
10V
5V
15V
10V
V
OUT3
V
OUT3
200mV/div
200mV/div
AC-COUPLED
AC-COUPLED
1A
0
1A
0
I
LX
I
LX
500mA/div
500mA/div
100µs/div
= 5.2V TO 10V, I = 300mA
OUT3
100µs/div
= 300mA
OUT3
V
IN
V
= 10V TO 15V, I
IN
6
_______________________________________________________________________________________
High-Efficiency, Triple-Output, Keep-Alive
Power Supply for Notebook Computers
Typical Operating Characteristics (continued)
(Circuit of Figure 1, V = +12V, PRESET = GND, T = +25°C, unless otherwise noted.)
IN
A
LDO DROPOUT VOLTAGE
vs. LOAD CURRENT
LDO DROPOUT VOLTAGE vs. V
OUT1
100
90
80
70
60
50
40
30
20
10
0
120
100
80
60
40
20
0
I
= 80mA
OUT1
0
10 20 30 40 50 60 70 80
2.5 2.6 2.7 2.8 2.9 3.0 3.1 3.2 3.3
(V)
I
(mA)
V
OUT1
OUT1
LDO PSRR vs. FREQUENCY
LDO LOAD TRANSIENT
MAX1534 toc15
70
60
100Ω LOAD
V
OUT1
20mV/div
AC-COUPLED
50
40
30
20
150mA
I
OUT1
50mA/div
10
0
0
0.01
0.1
1
10
100
20µs/div
FREQUENCY (kHz)
V
= 5V, I
= 10mA TO 150mA
OUT1
LDOIN
STARTUP WAVEFORMS
SHUTDOWN WAVEFORMS
MAX1534 toc17
MAX1534 toc16
SHDN
5V/div
SHDN
5V/div
0
0
V
OUT3
2V/div
V
OUT3
4V
V
OUT1
2V/div
V
OUT1
V
OUT_
2V/div
0
V
OUT2
V
OUT2
2V/div
0
0
0
0
0
POK
5V/div
POK
5V/div
1A
1A
0
I
LX
1A/div
I
LX
1A/div
0
100µs/div
100µs/div
= 33Ω, R
V
= 12V, R
= 33Ω, R
= 18Ω, R
= 50Ω
V
= 12V, R
= 18Ω, R
= 50Ω
OUT3
IN
OUT1
OUT2
OUT3
IN
OUT1
OUT2
_______________________________________________________________________________________
7
High-Efficiency, Triple-Output, Keep-Alive
Power Supply for Notebook Computers
Pin Description
PIN
NAME
FUNCTION
Shutdown Control Input. Drive SHDN above 1V to start up, and below 0.9V to shut down. LX is high
impedance in shut down, and supply current reduces to 3.5µA. Connect SHDN to IN for automatic
startup. SHDN can be connected to IN through a resistive voltage-divider to implement a
programmable undervoltage lockout.
1
SHDN
Open-Drain Power-OK (POK) Output. POK asserts low while any output voltage is below the reset
threshold. Connect a 100kΩ pullup resistor to OUT_. POK is driven low in shut down. If not used,
leave this pin unconnected.
2
POK
3
4
GND
ILIM
Ground. Connect backside pad to GND.
Peak LX Current Control Input. Connect to IN for 1000mA peak LX current. Connect to GND for
500mA peak LX current.
Inductor Connection. Connect LX to external inductor and diode as shown in Figure 1. Both LX pins
must be connected together on the PC board.
5, 8
6, 7
9
LX
IN
Buck Regulator Input Supply Voltage. Input voltage range is 4.5V to 24V. Both IN pins must be
connected together on the PC board.
Regulated LDO2 Output Voltage. Sources up to 160mA guaranteed. Bypass with 2.2µF (<0.2Ω
typical ESR) ceramic capacitor to GND.
OUT2
LDOIN
OUT1
BP
Input Supply for both LDOs. Supply voltage can range from 2.5V to 5.5V. Bypass with 2.2µF capacitor
to GND (see Capacitor Selection and LDO Stability).
10
11
12
13
14
Regulated LDO1 Output Voltage. Sources up to 160mA guaranteed. Bypass with 2.2µF (<0.2Ω
typical ESR) ceramic capacitor to GND.
LDO Reference Noise Bypass. Bypass with a low-leakage 0.01µF ceramic capacitor for reduced
noise at both outputs.
Feedback Input for LDO1. For a fixed 3.3V output, connect PRESET and FB1 to GND. For an
adjustable output, connect PRESET = IN and connect a resistive divider between OUT1 and GND.
FB1
Feedback Input for LDO2. For a fixed 1.8V output, connect PRESET and FB2 to GND. For an
adjustable output, connect PRESET = IN and connect a resistive divider between OUT2 and GND.
FB2
Preset Feedback Select Input. Connect to GND for the preset 5V buck output voltage, preset 3.3V
OUT1 output voltage, and preset 1.8V OUT2 output voltage. Connect PRESET to IN to select
adjustable feedback mode for all three regulators.
15
16
PRESET
Buck Output Feedback Input. For a fixed 5.0V output, connect PR ES E T to GND and FB3 to OUT3. For
an adjustable output, connect PR ES E T to IN and connect a resistive divider between OUT3 and GND.
FB3
only 1mW, and in shutdown mode, it draws only 3.5µA.
Detailed Description
The internal 24V switching MOSFET, internal current
sensing, and a high-switching frequency minimize PC
board space and component costs.
The MAX1534 regulator provides efficient light-load
power conversion for notebook computers or hand-held
devices that require keep-alive power or standby
power. The main step-down buck regulator uses a
unique peak current-limited control scheme, providing
high efficiency at light loads over a wide load range.
Operation up to 100% duty cycle allows the lowest pos-
sible dropout voltage, increasing the usable supply
voltage range. Under no load, the MAX1534 consumes
The MAX1534 includes two low-noise, low-dropout,
low-quiescent-current linear regulators. The linear regu-
lators are available with preset output voltages of 3.3V
and 1.8V. Each linear regulator can supply loads up to
160mA.
8
_______________________________________________________________________________________
High-Efficiency, Triple-Output, Keep-Alive
Power Supply for Notebook Computers
V
= +7V TO +24V
IN
10µF
IN
SHDN
POK
BP
L1
V
OUT3
= +5V ALWAYS
LX
C
OUT3
D1
0.01µF
PRESET
ILIM
MAX1534
100kΩ
FB3
FB1
FB2
V
= +3.3V ALWAYS
OUT1
OUT1
OUT2
V
= +5V ALWAYS
OUT3
LDOIN
V
= +1.8V ALWAYS
OUT2
2.2µF
2.2µF
2.2µF
GND
NOTE: SEE TABLE 1 FOR RECOMMENDED COMPONENT VALUES. SEE TABLE 2 FOR COMPONENT SUPPLIERS.
Figure 1. MAX1534 Typical Application Circuit
The MAX1534 PFM step-down topology consumes less
power than the traditional linear regulator solution when
converting from a high-input voltage source.
current is pulled through D1, and the current through the
inductor ramps back down, transferring the stored ener-
gy to the output capacitor and load. The MOSFET
remains off until the 0.42µs minimum off-time expires,
and the output voltage drops out of regulation.
Buck Converter
Current-Limited Control Architecture
The MAX1534’s buck converter uses a proprietary cur-
rent-limited control scheme with operation to 100% duty
cycle. This DC-to-DC converter pulses as needed to
maintain regulation, resulting in a variable switching fre-
quency that increases with the load. This eliminates the
high supply currents associated with conventional con-
stant-frequency pulse-width-modulation (PWM) con-
trollers that switch the MOSFET unnecessarily.
Current Limit (ILIM)
The MAX1534’s buck converter has an adjustable peak
current limit. Configure this peak current limit by con-
necting ILIM as shown in Table 3. Choose a current
limit that realistically reflects the maximum load current.
The maximum output current is half the peak current
limit. Although choosing a lower current limit allows
using an inductor with a lower current rating, it requires
a higher inductance (see Inductor Selection) and does
little to reduce inductor package size.
When the output voltage is too low, the error comparator
sets a flip-flop, which turns on the internal P-channel
MOSFET and begins a switching cycle (Figure 2). As
shown in Figure 3, the inductor current ramps up linearly,
storing energy in a magnetic field while charging the out-
put capacitor and servicing the load. The MOSFET turns
off when the peak current limit is reached, or when the
maximum on-time of 10µs is exceeded and the output
voltage is in regulation. If the output is out of regulation
and the peak current is never reached, the MOSFET
remains on, allowing a duty cycle up to 100%. This fea-
ture ensures the lowest possible dropout voltage. Once
the MOSFET turns off, the flip-flop resets, the inductor
ILIM can be dynamically switched to achieve the high-
est efficiency over the load range. (See Buck Efficiency
vs. Load Current (Circuit 1) in the Typical Operating
Characteristics.
Linear Regulators
Internal P-Channel Pass Transistor
The MAX1534 features two 1.5Ω P-channel MOSFET
pass transistors. A P-channel MOSFET provides sever-
al advantages over similar designs using PNP pass
transistors, including longer battery life. It requires no
_______________________________________________________________________________________
9
High-Efficiency, Triple-Output, Keep-Alive
Power Supply for Notebook Computers
Table 1. Recommended Components
CIRCUIT 1
CIRCUIT 2
Input voltage
Max frequency
On-time
7V
24V
175kHz
1µs
7V
71kHz
9µs
24V
160kHz
1µs
73kHz
8.8µs
Buck output
ILIM connection
5V, 500mA
IN
5V, 250mA
GND
15µH, 57mΩ, 1.60A
Sumida CDRH6D38R-150
33µH, 124mΩ, 1.10A
Sumida CDRH6D38R-330
L1
1A, 30V Schottky
Nihon EP10QY03
0.5A, 30V Schottky
Nihon EP05Q03L
D1
47µF, 6.3V, ceramic
TDK C3225X5R0J476M
33µF, 6.3V, ceramic
TDK C3225X5R0J336M
C
OUT3
Table 2. Component Suppliers
Table 3. Current-Limit Configuration
SUPPLIER
DIODES
WEBSITE
PEAK LX
MAXIMUM BUCK
ILIM
CURRENT LIMIT (mA) OUTPUT CURRENT (mA)
IN
1000
500
500
250
Central Semiconductor
Fairchild Semiconductor
General Semiconductor
International Rectifier
Nihon
www.centralsemi.com
www.fairchildsemi.com
www.gensemi.com
www.irf.com
GND
loads. The MAX1534 does not suffer from these prob-
lems. While a PNP-based regulator has dropout voltage
that is independent of the load, a P-channel MOSFET’s
dropout voltage is proportional to load current, provid-
ing for low dropout voltage at heavy loads and
extremely low dropout voltage at lighter loads.
www.niec.co.jp
ON Semiconductor
Vishay-Siliconix
Zetex
www.onsemi.com
www.vishay.com
www.zetex.com
CAPACITORS
AVX
Current Limit
The MAX1534 contain two independent current limiters,
one for each linear regulator, which monitor and control
the pass transistor’s gate voltage, limiting the guaran-
teed maximum output current to 160mA minimum. The
output can be shorted to ground for an indefinite time
without damaging the part.
www.avxcorp.com
www.kemet.com
Kemet
Nichicon
www.nichicon-us.com
www.sanyo.com
Sanyo
TDK
www.components.tdk.com
www.t-yuden.com
Taiyo Yuden
INDUCTORS
Coilcraft
Low-Noise Operation
An external 0.01µF bypass capacitor at BP, in conjunc-
tion with an internal resistor, creates a lowpass filter,
reducing the LDO output voltage noise.
www.coilcraft.com
www.cooperet.com
www.pulseeng.com
www.sumida.com
www.tokoam.com
Coiltronics
Pulse Engineering
Sumida USA
Toko
Shutdown (SHDN)
The MAX1534’s accurate SHDN input can be used as a
low-battery voltage detector. Drive SHDN above the 1V
input rising-edge trip level to start up the MAX1534.
The 100mV SHDN input hysteresis prevents the
MAX1534 from oscillating between startup and shut-
down. Drive SHDN low to shut down the MAX1534’s
buck converter and linear regulators. When in shut-
base drive, which reduces quiescent current signifi-
cantly. PNP-based regulators waste considerable cur-
rent in dropout when the pass transistor saturates, and
they also use high base-drive currents under large
10 ______________________________________________________________________________________
High-Efficiency, Triple-Output, Keep-Alive
Power Supply for Notebook Computers
IN
MAX1534
1V
VL
LX
REG
BP
TSDN
STARTUP
VL
REF
µ
0.01 F
IPEAK
VL
GND
PMOS
DRIVER
ZX
1V
VL
ENABLE
1V
SHDN
POK
FB3
OUT3_OK
OUT2_OK
LDOIN
PRESET
PRESET
LDOIN
OUT1_OK
0.9V
1V
OUT2_OK
1V
PMOS
DRIVER
PMOS
DRIVER
OUT1
OUT2
0.9V
LDOIN
OUT1_OK
FB1
FB2
0.9V
PRESET
PRESET
PRESET
PRESET
Figure 2. MAX1534 Functional Block Diagram
down, the supply current drops to 3.5µA, maximizing
battery life. The internal P-channel MOSFET in the buck
converter and linear regulators turn off to isolate each
input from its output. The output capacitance and load
current determine the rate at which the output voltage
decays. For automatic shutdown and startup, connect
SHDN to IN. Connect SHDN to IN through a resistive
voltage-divider to implement a programmable under-
voltage lockout. Do not leave SHDN floating.
cator. Connect a capacitor from POK to GND to pro-
duce a delayed POK signal (delay set by the RC time
constant). POK is low in shutdown and is high imped-
ance when all three outputs are in regulation.
Thermal-Overload Protection
Thermal-overload protection limits total power dissipation
in the MAX1534. When the junction temperature exceeds
T = +160°C, a thermal sensor turns off the pass transis-
J
tor, allowing the IC to cool. The thermal sensor turns the
IC on again after the IC’s junction temperature cools by
15°C, resulting in a pulsed output during continuous
thermal-overload conditions.
Power-OK (POK)
The open-drain POK output is useful as a simple error
flag, as well as a delayed reset output. POK sinks cur-
rent when any of the three regulated output voltages is
11% below its regulation point. Connect POK to OUT_
through a high-value resistor for a simple error flag indi-
Thermal-overload protection is designed to protect the
MAX1534 in the event of fault conditions. For continu-
______________________________________________________________________________________ 11
High-Efficiency, Triple-Output, Keep-Alive
Power Supply for Notebook Computers
ous operation, do not exceed the absolute maximum
Table 4. PRESET Setting
junction temperature rating of T = +150°C.
J
PRESET
MODE
OUT_ AND FB_
Operating Region and Power Dissipation
The MAX1534’s maximum power dissipation depends
on the thermal resistance of the case and circuit board,
the temperature difference between the die junction
and ambient air, and the rate of air flow. The power dis-
sipated in the device is the sum of the buck MOSFET
switching and conduction losses and the linear regula-
tors’ conduction losses. The maximum power dissipa-
tion is:
IN
Adjustable
FB_ regulates to 1.0V
OUT1 = 3.3V, FB1 = GND,
OUT2 = 1.8V, FB2 = GND,
OUT3 = FB3 = 5.0V
GND
Preset
15mV, the output can be set using fixed resistors
instead of trim pots.
Design Procedure
P
MAX
= (T - T ) / (θ + θ
)
BA
J
A
JB
Buck Converter
where T - T is the temperature difference between the
J
A
Inductor Selection
When selecting the inductor, consider these four para-
meters: inductance value, saturation rating, series
resistance, and size. The MAX1534 operates with a
wide range of inductance values. For most applica-
tions, values between 10µH and 50µH work best with
the controller’s high switching frequency. Larger induc-
tor values reduce the switching frequency and thereby
improve efficiency and EMI. The trade-off for improved
efficiency is a higher output ripple and slower transient
response. On the other hand, low-value inductors
respond faster to transients, improve output ripple, offer
smaller physical size, and minimize cost. If the inductor
value is too small, the peak inductor current exceeds
the current limit due to current-sense comparator prop-
agation delay, potentially exceeding the inductor’s cur-
rent rating. Calculate the minimum inductance value as
follows:
MAX1534 die junction and the surrounding air, θ (or
JB
θ
JC
) is the thermal resistance of the package, and θ is
BA
the thermal resistance through the printed circuit board,
copper traces, and other materials to the surrounding
air. The exposed backside pad of the MAX1534 pro-
vides a low thermal impedance to channel heat out of
the package. Connect the exposed backside pad to
ground using a large pad or ground plane.
Preset and Adjustable Output Voltages
(PRESET)
The MAX1534 features dual mode operation; it oper-
ates in either a preset voltage mode (see Table 4) or an
adjustable mode. In preset voltage mode, internal
trimmed feedback resistors set the MAX1534 outputs to
3.3V for V
, 1.8V for V
, and 5.0V for FB3 (buck
OUT2
OUT1
regulator). Select this mode by connecting PRESET to
ground. Connect PRESET to IN to operate the
MAX1534 in the adjustable mode. Select an output volt-
age using two external resistors connected as a volt-
age-divider to FB_ (Figure 4). The output voltage is set
by the following equation:
V
-V
× t
(
)
IN(MAX) OUT3
ON(MIN)
L
=
(MIN)
I
LX(PEAK)
where t
= 0.5µs.
ON(MIN)
R
R
TOP_
V
= V
1+
The inductor’s saturation current rating must be greater
than the peak switch current limit, plus the overshoot
due to the 150ns current-sense comparator propaga-
tion delay. Saturation occurs when the inductor’s mag-
netic flux density reaches the maximum level the core
can support and the inductance starts to fall. Choose
OUT_
FB_
BOT_
where V
= 1.0V, V
and V
can range from
FB_
1.0V to V
OUT1
OUT3
OUT2
, and V
can range from 1.0V to V .
To simplify resistor selection:
LDOIN
IN
an inductor with a saturation rating greater than I
in the following equation:
PEAK
V
OUT_
R
= R
−1
TOP_
BOT_
V
FB_
I
= I
+ (V - V
) ✕ 150ns / L
OUT3
PEAK
LX(PEAK)
IN
Inductor series resistance affects both efficiency and
dropout voltage (see the Buck Dropout Performance
section).
Choose R
= 100kΩ to optimize power consump-
BOT_
tion, accuracy, and high-frequency power-supply rejec-
tion. The total current through the external resistive
feedback and load resistors should not be less than
High series resistance limits the maximum current avail-
able at lower input voltages, and increases the dropout
10µA. Since the V
tolerance is typically less than
FB_
12 ______________________________________________________________________________________
High-Efficiency, Triple-Output, Keep-Alive
Power Supply for Notebook Computers
V
OUT1
PRESET
IN
OUT1
V
= +7V TO +24V
IN
V
OUT3
50mV/div
R
TOP1
AC-COUPLED
FB1
V
OUT3
10V
0
MAX1534
V
LX
10V/div
LX
R
BOT1
R
TOP3
BOT3
V
OUT2
1A
OUT2
FB2
FB3
I
LX
500mA/div
R
TOP2
R
0
GND
4µs/div
= 300mA
R
BOT2
V
= 12V, I
OUT3
IN
Figure 3. Normal Buck Operation
Figure 4. Adjustable Output Voltages
voltage. For optimum performance, select an inductor
with the lowest possible DC resistance that fits in the
allotted dimensions. Some recommended component
manufacturers are listed in Table 2.
2
L ×(I
−I
× V
)
V
PEAK OUT3
IN
V
=
RIPPLE(C)
2C
V − V
IN OUT3
OUT3
OUT3
where I
is the peak inductor current (see Inductor
PEAK
Maximum Buck Output Current
The MAX1534’s buck converter’s maximum output cur-
rent is limited by the peak inductor current. For the typi-
cal application, the maximum output current is
approximately:
Selection). The worst-case ripple occurs at no load.
These equations are suitable for initial capacitor selec-
tion, but final values should be set by testing a proto-
type or evaluation circuit. As a general rule, a smaller
amount of charge delivered in each pulse results in
less output ripple. Since the amount of charge deliv-
ered in each oscillator pulse is determined by the
inductor value and input voltage, the voltage ripple
increases with larger inductance, and as the input volt-
age decreases. See Table 1 for recommended capaci-
tor values and Table 2 for recommended component
manufacturers.
I
= 1/2 I
LX (PEAK)(MIN)
OUT3(MAX)
For low-input voltages, the maximum on-time can be
reached and the load current is limited by:
I
= 1/2 (V - V
) ✕ 10µs / L
OUT3
OUT3
IN
Note that any current provided by the linear regulators
comes from the buck regulator and subtracts from the
maximum current that the buck provides for other loads.
Buck Input Capacitor Selection
The input filter capacitor reduces peak currents drawn
from the power source and reduces noise and voltage
ripple on the input caused by the circuit’s switching.
The input capacitor must meet the ripple-current
Buck Output Capacitor Selection
Choose the output capacitor to service the maximum
load current with acceptable voltage ripple. The output
ripple has two components: variations in the charge
stored in the output capacitor with each LX pulse, and
the voltage drop across the capacitor’s equivalent
series resistance (ESR) caused by the current into and
out of the capacitor:
requirement (I
) imposed by the switching current
RMS
defined by the following equation:
I
× V
4
3
V
IN
OUT3
OUT3
I
=
×
−1
RMS
V
≅ V
+ V
RIPPLE(ESR) RIPPLE(C)
RIPPLE
V
V
IN
OUT3
The output voltage ripple as a consequence of the ESR
and output capacitance is:
For most applications, nontantalum chemistries (ceram-
ic, aluminum, polymer, or OSCON) are preferred due to
their robustness to high inrush currents typical of sys-
tems with low-impedance battery inputs. Choose an
V
= ESR ✕ I
PEAK
RIPPLE(ESR)
______________________________________________________________________________________ 13
High-Efficiency, Triple-Output, Keep-Alive
Power Supply for Notebook Computers
input capacitor that exhibits less than +10°C tempera-
ture rise at the RMS input current for optimal circuit
longevity.
V
= I
✕ (R + R
LX
)
INDUCTOR
DROPOUT(BUCK)
OUT3
LDO PSRR
The MAX1534’s linear regulators are designed to deliv-
er low dropout voltages and low quiescent currents in
battery-powered systems. Power-supply rejection is
55dB at low frequencies and rolls off above 20kHz.
(See the LDO PSRR vs. Frequency graph in the Typical
Operating Characteristics.)
Diode Selection
The current in the external diode (D1 in Figure 1)
changes abruptly from zero to its peak value each time
the LX switch turns off. To avoid excessive losses, the
diode must have a fast turn-on time and a low forward
voltage. Make sure that the diode’s peak current rating
exceeds the peak current set by the current limit, and
To improve supply-noise rejection and transient
response, increase the values of the input and output
bypass capacitors or use passive filtering techniques.
that its breakdown voltage exceeds V . Use Schottky
IN
diodes when possible.
LDO Dropout Voltage
A linear regulator’s minimum input-output voltage differ-
ential (or dropout voltage) determines the lowest usable
supply voltage. Because the MAX1534 uses a P-chan-
nel MOSFET pass transistor, its dropout voltage is a
Linear Regulators
Capacitor Selection and LDO Stability
Use a 2.2µF capacitor on the MAX1534 LDOIN pin and
a 2.2µF capacitor on the outputs. Larger input capaci-
tor values and lower ESRs provide better supply-noise
rejection and line-transient response. To reduce noise,
improve load transients, and for loads up to 160mA,
use larger output capacitors (up to 10µF). For stable
operation over the full temperature range and with load
currents up to 80mA, use 2.2µF. Note that some ceram-
ic dielectrics exhibit large capacitance and ESR varia-
tion with temperature. With dielectrics such as Z5U and
Y5V, it may be necessary to use 4.7µF or more to
ensure stability at temperatures below -10°C. With X7R
or X5R dielectrics, 2.2µF is sufficient at all operating
temperatures. These regulators are optimized for
ceramic capacitors, and tantalum capacitors are not
recommended.
function of drain-to-source on-resistance (R
)
DS(ON)
multiplied by the load current (see LDO Dropout
Voltage vs. Load Current in the Typical Operating
Characteristics).
PC Board Layout Guidelines
High switching frequencies and large peak currents
make PC board layout an important part of the design.
Poor layout introduces switching noise into the feedback
path, resulting in jitter, instability, or degraded perfor-
mance. High current traces, highlighted in the Typical
Application Circuit (Figure 1), should be as short and
wide as possible. Additionally, the current loops formed
by the power components (C , C
, L1, and D1)
OUT3
IN
should be as short as possible to avoid radiated noise.
Connect the ground pins of these power components at
a common node in a star-ground configuration.
Separate the noisy traces, such as the LX node, from
the feedback network with grounded copper.
Furthermore, keep the extra copper on the board and
integrate it into a pseudoground plane. When using
external feedback, place the resistors as close to the
feedback pin as possible to minimize noise coupling.
Use a 0.01µF bypass capacitor at BP for low output volt-
age noise. Increasing the capacitance slightly decreas-
es the output noise, but increases the startup time.
Applications Information
Buck Dropout Performance
A step-down converter’s minimum input-to-output volt-
age differential (dropout voltage) determines the lowest
usable supply voltage. In battery-powered systems,
this limits the useful end-of-life battery voltage. To maxi-
mize battery life, the MAX1534 operates with duty
cycles up to 100%, which minimizes the dropout volt-
age and eliminates switching losses while in dropout.
When the supply voltage approaches the output volt-
age, the P-channel MOSFET remains on continuously to
supply the load.
For a step-down converter with 100% duty cycle,
dropout depends on the MOSFET drain-to-source on-
resistance and inductor series resistance; therefore, it
is proportional to the load current:
14 ______________________________________________________________________________________
High-Efficiency, Triple-Output, Keep-Alive
Power Supply for Notebook Computers
Pin Configuration
Chip Information
TRANSISTOR COUNT: 1512
FB3 PRESET FB2
FB1
13
PROCESS: BiCMOS
16
15
14
SHDN
1
12
11
BP
OUT1
2
3
4
POK
GND
ILIM
MAX1534
10 LDOIN
OUT2
9
5
6
7
8
LX
IN
IN
LX
16 THIN QFN
______________________________________________________________________________________ 15
High-Efficiency, Triple-Output, Keep-Alive
Power Supply for Notebook Computers
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.)
PACKAGE OUTLINE
12,16,20,24L QFN THIN, 4x4x0.8 mm
21-0139
A
PACKAGE OUTLINE
12,16,20,24L QFN THIN, 4x4x0.8 mm
21-0139
A
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.
16 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2002 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
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