MAX8507ETE [MAXIM]
PWM Step-Down DC-DC Converters with 75m? Bypass FET for WCDMA and cdmaOne Handsets; PWM降压型75mΩ旁路FET的DC -DC转换器,用于WCDMA和cdmaOne手机型号: | MAX8507ETE |
厂家: | MAXIM INTEGRATED PRODUCTS |
描述: | PWM Step-Down DC-DC Converters with 75m? Bypass FET for WCDMA and cdmaOne Handsets |
文件: | 总12页 (文件大小:385K) |
中文: | 中文翻译 | 下载: | 下载PDF数据表文档文件 |
19-2918; Rev 1; 1/04
PWM Step-Down DC-DC Converters with 75mΩ
Bypass FET for WCDMA and cdmaOne Handsets
General Description
Features
The MAX8506/MAX8507/MAX8508 integrate a PWM step-
down DC-DC regulator and a 75mΩ (typ) bypass FET to
power the PA in WCDMA and cdmaOne™ cell phones.
The supply voltage range is from 2.6V to 5.5V, and the
guaranteed output current is 600mA. One megahertz
PWM switching allows for small external components.
♦ Integrated 75mΩ (typ) Bypass FET
♦ 38mV Dropout at 600mA Load
♦ Up to 94% Efficiency
♦ Dynamically Adjustable Output from 0.4V to 3.4V
(MAX8506, MAX8507)
The MAX8506 and MAX8507 are dynamically controlled
to provide varying output voltages from 0.4V to 3.4V. The
MAX8508 is externally programmed for fixed 0.75V to
3.4V output. Digital logic enables a high-power (HP)
bypass mode that connects the output directly to the bat-
tery for all versions. The MAX8506/MAX8507/MAX8508
are designed so the output settles in less than 30µs for a
full-scale change in output voltage and load current.
♦ Externally Fixed Output from 0.75V to 3.4V
(MAX8508)
♦ 1MHz Fixed-Frequency PWM Switching
♦ 600mA Guaranteed Output Current
♦ Shutdown Mode 0.1µA (typ)
♦ 16-Pin Thin QFN (4mm x 4mm, 0.8mm max Height)
The MAX8506/MAX8507/MAX8508 are offered in 16-pin
4mm x 4mm thin QFN packages (0.8mm max height).
Ordering Information
Applications
WCDMA/NCDMA Cell Phones
PART
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
16 Thin QFN
16 Thin QFN
16 Thin QFN
Wireless PDAs, Palmtops, and Notebook
Computers
MAX8506ETE
MAX8507ETE
MAX8508ETE
Wireless Modems
Pin Configurations appear at end of data sheet.
cdmaOne is a trademark of CDMA Development Group.
Typical Application Circuits (MAX8506/MAX8507)
OUTPUT
0.4V TO 3.4V OR V
INPUT
2.6V TO 5.5V
4.7µH
BATT
4.7µF
2.2µF
BATTP
LX
BATT
OUT
0.075Ω
MAX8506
MAX8507
SKIP
SHDN
REF
CURRENT-
LIMIT
CONTROL
REF
0.4Ω
0.3Ω
PWM
0.22µF
1MHz
OSC
REFIN
DAC
HP
GND
PGND
COMP
R *
C
C *
f
*
R
C
(kΩ)
10
15
C (pF) C (pF)
C f
MAX8506
MAX8507
1500
1000
100
100
C *
C
Typical Application Circuits continued at end of data sheet.
________________________________________________________________ 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.
PWM Step-Down DC-DC Converters with 75mΩ
Bypass FET for WCDMA and cdmaOne Handsets
ABSOLUTE MAXIMUM RATINGS
Continuous Power Dissipation (T = +70°C)
A
BATTP, BATT, OUT, SHDN, SKIP, HP, REFIN,
16-Pin Thin QFN (derate 16.9mW/°C above +70°C) ...1.349W
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
FB to GND ...........................................................-0.3V to +6V
PGND to GND .......................................................-0.3V to +0.3V
BATT to BATTP......................................................-0.3V to +0.3V
OUT, COMP, REF to GND.......................-0.3V to (V
+ 0.3V)
BATT
LX Current (Note 1)...............................................................1.6A
OUT Current (Note 1)............................................................3.2A
Output Short-Circuit Duration.....................................Continuous
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.
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
= V
= 3.6V, SHDN = SKIP = BATT, HP = GND, V
= 1.932V (MAX8506), V
= 1.70V (MAX8507),
REFIN
BATT
BATTP
REFIN
C
REF
= 0.22µF, T = -40°C to +85°C, unless otherwise noted. Typical values are at T = +25°C.) (Note 2)
A
A
PARAMETER
CONDITIONS
MIN
2.6
TYP
MAX
5.5
UNITS
Input BATT Voltage
V
V
Undervoltage Lockout Threshold
Undervoltage Lockout Hysteresis
V
rising
2.150
2.35
40
2.575
BATT
mV
SKIP = GND (normal mode)
SKIP = BATT, 1MHz switching
HP = BATT
180
1750
775
0.1
250
Quiescent Current
µA
Quiescent Current in Dropout
Shutdown Supply Current
1000
5
µA
µA
SHDN = GND
V
V
V
V
= 1.932V, I
= 0.426V, I
= 1.700V, I
= 0.375V, I
= 0 to 600mA (MAX8506)
= 0 to 30mA (MAX8506)
= 0 to 600mA (MAX8507)
= 0 to 30mA (MAX8507)
3.375
0.740
3.375
0.740
250
3.40
0.75
3.40
0.75
485
535
0.1
3.425
0.760
3.425
0.760
REFIN
REFIN
REFIN
REFIN
OUT
OUT
OUT
OUT
OUT Voltage Accuracy
V
MAX8506
MAX8507
OUT Input Resistance
REFIN Input Current
REFIN to OUT Gain
kΩ
µA
275
-1
+1
MAX8506
MAX8507
1.76
2.00
1.25
2.5
V/V
Reference Voltage
1.225
1.275
8.5
V
mV
µF
V
Reference Load Regulation
Reference Bypass Capacitor
FB Voltage Accuracy
FB Input Current
10µA < I
< 100µA
REF
0.1
0.22
0.75
0.03
0.4
FB = COMP (MAX8508)
= 1V (MAX8508)
0.7275
0.7725
0.175
0.825
V
µA
FB
V
V
V
V
= 3.6V
= 2.6V
= 3.6V
= 2.6V
BATT
BATT
BATT
BATT
P-Channel On-Resistance
N-Channel On-Resistance
I
I
I
= 180mA
= 180mA
Ω
Ω
Ω
LX
0.5
0.3
0.5
LX
0.35
HP/Bypass P-Channel
On-Resistance
= 180mA, V
= 3.6V
0.075
0.110
OUT
BATT
2
_______________________________________________________________________________________
PWM Step-Down DC-DC Converters with 75mΩ
Bypass FET for WCDMA and cdmaOne Handsets
ELECTRICAL CHARACTERISTICS (continued)
(V
= V
= 3.6V, SHDN = SKIP = BATT, HP = GND, V
= 1.932V (MAX8506), V
= 1.70V (MAX8507),
REFIN
BATT
BATTP
REFIN
C
REF
= 0.22µF, T = -40°C to +85°C, unless otherwise noted. Typical values are at T = +25°C.) (Note 2)
A
A
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
P-Channel Current-Limit
Threshold
1.00
1.25
1.50
A
SKIP = BATT (PWM mode)
-0.6
-0.45
0.05
-0.30
0.07
N-Channel Current-Limit
Threshold
A
A
A
SKIP = GND (normal mode)
0.03
P-Channel Pulse-Skipping
Current Threshold
SKIP = GND (normal mode)
0.050
0.8
0.125
1.5
0.170
2.5
HP/Bypass P-Channel
Current-Limit Threshold
V
= 3.1V
OUT
LX Leakage Current
OUT Leakage Current
Maximum Duty Cycle
-2
-2
0.01
0.01
+2
+2
µA
µA
%
100
SKIP = GND (normal mode)
SKIP = BATT
0
Minimum Duty Cycle
%
12
COMP Clamp Low Voltage
COMP Clamp High Voltage
0.8
2.0
V
V
MAX8506
MAX8507
MAX8508
85
75
150
130
260
0.48
215
188
376
0.60
Transconductance
µS
V/A
150
0.36
Current-Sense Transresistance
OSCILLATOR
Internal Oscillator Frequency
LOGIC INPUTS (SHDN, HP, SKIP)
Logic-Input High Voltage
Logic-Input Low Voltage
Logic Input Current
0.8
1.6
1
1.2
MHz
V
V
= 2.6V to 5.5V
= 2.6V to 5.5V
V
V
BATT
BATT
0.4
1
0.1
µA
THERMAL SHUTDOWN
Thermal-Shutdown Temperature
Thermal-Shutdown Hysteresis
+160
15
°C
°C
Note 2: Specifications to -40°C are guaranteed by design, not production tested.
_______________________________________________________________________________________
3
PWM Step-Down DC-DC Converters with 75mΩ
Bypass FET for WCDMA and cdmaOne Handsets
Typical Operating Characteristics
(V
BATT
= V
= 3.6V, SHDN = SKIP = BATT, HP = GND, T = +25°C, unless otherwise noted.) (See the Typical Application Circuits.)
BATTP A
EFFICIENCY vs. OUTPUT VOLTAGE
IN NORMAL MODE
EFFICIENCY vs. OUTPUT VOLTAGE
IN PWM MODE
EFFICIENCY vs. INPUT VOLTAGE
100
90
80
70
60
50
100
100
90
80
70
60
50
R
LOAD
= 15Ω
R
LOAD
= 15Ω
90
80
70
60
50
V
OUT
= 3.4V
R
LOAD
= 10Ω
R
LOAD
= 10Ω
R
LOAD
= 5Ω
R
LOAD
= 5Ω
V
OUT
= 1.2V
V
OUT
= 0.4V
SKIP = GND
R
LOAD
= 10Ω
SKIP = GND
2.5
3.0
3.5
4.0
4.5
5.0
5.5
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5
OUTPUT VOLTAGE (V)
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5
OUTPUT VOLTAGE (V)
INPUT VOLTAGE (V)
SUPPLY CURRENT vs. SUPPLY VOLTAGE
IN PWM MODE
EFFICIENCY vs. LOAD CURRENT
DROPOUT VOLTAGE vs. LOAD CURRENT
100
90
80
70
60
50
150
120
90
60
30
0
6
5
4
3
2
1
0
V
IN
= 3.6V
V
OUT
= 2.5V;
HP = BATT
NORMAL MODE
V
OUT
= 1.2V
V
OUT
= 1.2V;
V
OUT
= 0.4V
PWM
V
OUT
= 2.5V;
PWM
V
OUT
= 1.2V;
NORMAL MODE
1
10
100
1000
0
500
1000
1500
2000
2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5
SUPPLY VOLTAGE (V)
LOAD CURRENT (mA)
LOAD CURRENT (mA)
SUPPLY CURRENT vs. SUPPLY VOLTAGE
IN NORMAL MODE
HEAVY-LOAD SWITCHING WAVEFORM
MAX8506 toc08
1000
900
800
700
600
500
400
300
200
100
SKIP = GND
V
LX
2V/div
V
OUT
= 3.4V
V
OUT
AC-COUPLED
20mV/div
V
OUT
= 1.2V
V
OUT
= 0.4V
V
OUT
= 1.2V
LOAD = 10Ω
2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5
SUPPLY VOLTAGE (V)
1µs/div
4
_______________________________________________________________________________________
PWM Step-Down DC-DC Converters with 75mΩ
Bypass FET for WCDMA and cdmaOne Handsets
Typical Operating Characteristics (continued)
(V
BATT
= V
= 3.6V, SHDN = SKIP = BATT, HP = GND, T = +25°C, unless otherwise noted.) (See the Typical Application Circuits.)
BATTP A
LIGHT-LOAD SWITCHING WAVEFORM
LIGHT-LOAD SWITCHING WAVEFORM
IN PWM MODE
IN NORMAL MODE
MAX8506 toc09
MAX8506 toc10
V
LX
V
LX
2V/div
2V/div
V
OUT
V
OUT
AC-COUPLED
5mV/div
AC-COUPLED
20mV/div
V
OUT
= 0.4V
V
OUT
= 0.4V
LOAD = 10Ω, SKIP = GND
LOAD = 10Ω
1µs/div
400µs/div
EXITING AND ENTERING SHUTDOWN
REFIN TRANSIENT RESPONSE
MAX8506 toc11
MAX8506 toc12
REFIN
1V/div
SHDN
2V/div
0
0
SKIP = GND
V
OUT
V
1V/div
OUT
1V/div
SKIP = BATT
= 0.284V TO 1.420V
V
REFIN
V
OUT
= 1.8V, R
= 10Ω
LOAD
100µs/div
20µs/div
LINE TRANSIENT RESPONSE
HP TRANSIENT RESPONSE
MAX8506 toc14
MAX8506 toc13
HP
1V/div
V
IN
200mV/div
0
3.4V
SKIP = GND
V
OUT
V
OUT
1V/div
AC-COUPLED
20mV/div
SKIP = BATT
= 10Ω
1.8V
V
OUT
= 1.2V, R
= 10Ω
LOAD
V
OUT
= 1.8V, R
LOAD
20µs/div
20µs/div
_______________________________________________________________________________________
5
PWM Step-Down DC-DC Converters with 75mΩ
Bypass FET for WCDMA and cdmaOne Handsets
Pin Description
PIN
NAME
FUNCTION
MAX8506
MAX8507
MAX8508
Shutdown Control Input. Drive low for shutdown mode. Connect to BATT or logic high to
enable the IC.
1
2
3
1
2
3
SHDN
GND
REF
Ground. Connect to PGND and directly to EP.
Reference Output. Output of the internal 1.25V reference. Bypass to GND with a 0.22µF
capacitor.
External Reference Input. Connect to the output of a digital-to-analog converter for
dynamic adjustment of the output voltage.
4
5
—
5
REFIN
COMP
Compensation. Connect a compensation network from COMP to GND to stabilize the
regulator. See the Typical Application Circuits.
High-Power Bypass Control Input. Drive low for OUT to regulate to the voltage set by
REFIN (MAX8506/MAX8507) or the external resistors on FB (MAX8508). Drive HP high for
OUT to be connected to BATT by an internal bypass PFET.
6
6
HP
7
8
7
8
N.C.
No Connection. Connect to PGND.
Power Ground. Connect to GND.
PGND
Inductor Connection to the Drains of the Internal Power MOSFETs. LX is high impedance
in shutdown mode.
9
9
LX
Supply Voltage Input. Connect to a 2.6V to 5.5V source. Bypass BATTP to PGND with a
low-ESR 2.2µF capacitor. Connect BATTP to BATT.
10
10
BATTP
11, 13, 15
12, 14
11, 13, 15
12, 14
BATT
OUT
Supply Voltage Input. Connect all BATT pins to BATTP.
Regulator Output. Connect both OUT pins directly to the output voltage.
Skip Control Input. Connect to GND or drive low to enable pulse skipping under light
loads. Connect SKIP to BATT or logic high for forced-PWM mode.
16
16
SKIP
Output Feedback Sense Input. To set the output voltage, connect FB to the center of an
external resistive voltage-divider between OUT and GND. FB voltage regulates to 0.75V
when HP is low.
—
—
4
FB
EP
—
Exposed Pad. Connect directly to GND underneath the IC.
ponent size. Each device includes an internal synchro-
Detailed Description
nous rectifier for high efficiency, which eliminates the
need for an external Schottky diode. The normal operat-
ing mode uses constant-frequency PWM switching at
medium and heavy loads and automatically pulse skips
at light loads to reduce supply current and extend bat-
tery life. A forced-PWM mode switches at a constant
frequency, regardless of load, to provide a well-con-
trolled spectrum in noise-sensitive applications. Battery
life is maximized by the low-dropout (75mΩ) high-
power mode and a 0.1µA (typ) logic-controlled shut-
down mode.
The MAX8506/MAX8507/MAX8508 PWM step-down DC-
DC converters with integrated bypass PFET are opti-
mized for low-voltage, battery-powered applications
where high efficiency and small size are priorities. An
analog control signal dynamically adjusts the MAX8506/
MAX8507s’ output voltage from 0.4V to 3.4V with a set-
tling time of 30µs. The MAX8508 uses external feedback
resistors to set the output voltage from 0.75V to 3.4V.
The MAX8506/MAX8507/MAX8508 operate at a high
1MHz switching frequency that reduces external com-
6
_______________________________________________________________________________________
PWM Step-Down DC-DC Converters with 75mΩ
Bypass FET for WCDMA and cdmaOne Handsets
Then the main switch turns off and the magnetic field in
the inductor collapses while current flows through the
synchronous rectifier to the output filter capacitor and
the load. The synchronous rectifier is turned off when
the inductor current reaches zero. The MAX8506/
MAX8507/MAX8508 wait until the skip comparator
senses a low output voltage again.
PWM Control
The MAX8506/MAX8507/MAX8508 use a fixed-frequen-
cy, current-mode and PWM controller capable of achiev-
ing 100% duty cycle. Current-mode feedback provides
cycle-by-cycle current limiting and superior load and line
response, as well as overcurrent protection for the inter-
nal MOSFET and rectifier. A comparator at the P-channel
MOSFET switch detects overcurrent at 1.25A.
Forced-PWM Operation
Connect SKIP to BATT for forced-PWM operation.
Forced-PWM operation is desirable in sensitive RF and
data-acquisition applications to ensure that switching
harmonics do not interfere with sensitive IF and data-
sampling frequencies. A minimum load is not required
during forced-PWM operation since the synchronous
rectifier passes reverse-inductor current as needed to
allow constant-frequency operation with no load. Forced-
PWM operation uses higher supply current with no load
(1.75mA typ) compared to skip mode (180µA typ).
During PWM operation, the MAX8506/MAX8507/
MAX8508 regulate the output voltage by switching at a
constant frequency and then modulating the duty cycle
with PWM control. The error-amp output, the main
switch current-sense signal, and the slope-compensa-
tion ramp are all summed using a PWM comparator.
The comparator modulates the output power by adjust-
ing the peak inductor current during the first half of
each cycle based on the output-error voltage. The
MAX8506/MAX8507/MAX8508 have relatively low AC
loop gain coupled with a high-gain integrator to enable
the use of a small and low-valued output filter capaci-
tor. The resulting load regulation is 0.1% at 0 to 600mA.
100% Duty-Cycle Operation and Dropout
The maximum on-time can exceed one internal oscilla-
tor cycle, which permits operation at 100% duty cycle.
Near dropout, cycles can be skipped, reducing switch-
ing frequency. However, voltage ripple remains small
because the current ripple is still low. As the input volt-
age drops even further, the duty cycle increases until
the internal P-channel MOSFET stays on continuously.
Dropout voltage at 100% duty cycle is the output cur-
rent multiplied by the sum of the internal PMOS on-
resistance (400mΩ typ) and the inductor resistance.
For lower dropout, use the high-power bypass mode
(75mΩ typ).
Normal-Mode Operation
Connecting SKIP to GND enables normal operation. This
allows automatic PWM control at medium and heavy
loads and skip mode at light loads to improve efficiency
and reduce quiescent current to 180µA. Operating in
normal mode allows the MAX8506/MAX8507/MAX8508
to pulse skip when the peak inductor current drops
below 90mA. During skip operation, the MAX8506/
MAX8507/MAX8508 switch only as needed to service
the load, reducing the switching frequency and associat-
ed losses in the internal switch and synchronous rectifier.
High-Power Bypass Mode
A high-power bypass mode is available for use when a
PA transmits at high power. This mode connects OUT
to BATT through the bypass PFET. Additionally, the
PWM buck converter is forced into 100% duty cycle to
further reduce dropout. The dropout in the bypass
PFET equals the load current multiplied by the on-resis-
tance (75Ω typ) in parallel with the buck converter and
inductor dropout resistance.
There are three steady-state operating conditions for
the MAX8506/MAX8507/MAX8508 in normal mode:
1) The device performs in continuous conduction for
heavy loads in a manner identical to forced-PWM
mode. 2) The inductor current becomes discontinuous
at medium loads, requiring the synchronous rectifier to
be turned off before the end of a cycle as the inductor
current reaches zero. 3) The device enters into skip
mode when the converter output voltage exceeds its
regulation limit before the inductor current reaches its
skip threshold level.
Undervoltage Lockout (UVLO)
The MAX8506/MAX8507/MAX8508 do not operate with
battery voltages below the UVLO threshold of 2.35V
(typ). The output remains off until the supply voltage
exceeds the UVLO threshold. This guarantees the
integrity of the output voltage regulation.
During skip mode, a switching cycle initiates when the
output voltage has dropped out of regulation. The P-
channel MOSFET switch turns on and conducts current
to the output-filter capacitor and load until the inductor
current reaches the pulse-skipping current threshold.
_______________________________________________________________________________________
7
PWM Step-Down DC-DC Converters with 75mΩ
Bypass FET for WCDMA and cdmaOne Handsets
The MAX8506/MAX8507s’ output voltage is dynamically
adjustable from 0.4V to 3.4V by the use of the REFIN
Synchronous Rectification
An N-channel synchronous rectifier operates during the
second half of each switching cycle (off-time). When
the inductor current falls below the N-channel current-
comparator threshold or when the PWM reaches the
end of the oscillator period, the synchronous rectifier
turns off. This prevents reverse current from the output
to the input in pulse-skipping mode. During PWM oper-
ation, the NEGLIM threshold adjusts to permit reverse
current during light loads. This allows regulation with a
constant switching frequency and eliminates minimum
load requirements for fixed-frequency operation.
input. The gain from V
to V
is internally set to
REFIN
OUT
1.76 (MAX8506) or 2.00 (MAX8507). V
can be adjust-
OUT
ed during operation by driving REFIN with an external
DAC. The MAX8506/MAX8507 output responds to full-
scale change in voltage and current in less than 30µs.
Using External Divider (MAX8508)
The MAX8508 is intended for two-step V
control
CC
applications where high efficiency is a priority. Select
an output voltage between 0.75V and 3.4V by connect-
ing FB to a resistive-divider between the output and
GND (see the MAX8508 Typical Application Circuit).
Select feedback resistor R2 in the 5kΩ to 50kΩ range.
R1 is then given by:
Shutdown Mode
Drive SHDN to GND to place the MAX8506/MAX8507/
MAX8508 in shutdown mode. In shutdown, the refer-
ence, control circuitry, internal switching MOSFET, and
synchronous rectifier turn off and the output becomes
high impedance. Input current falls to 0.1µA (typ) dur-
ing shutdown mode. Drive SHDN high to enable the IC.
V
V
OUT
R1 = R2 ×
−1
FB
where V = 0.75V.
FB
Current-Sense Comparators
The MAX8506/MAX8507/MAX8508 use several internal
current-sense comparators. In PWM operation, the PWM
comparator terminates the cycle-by-cycle on-time and
provides improved load and line response. A second cur-
rent-sense comparator used across the P-channel switch
controls entry into skip mode. A third current-sense com-
parator monitors current through the internal N-channel
MOSFET to prevent excessive reverse currents and
determine when to turn off the synchronous rectifier. A
fourth comparator used at the P-channel MOSFET
detects overcurrent. A fifth comparator used at the
bypass P-channel MOSFET detects overcurrent in the
HP mode or at dropout. This protects the system, exter-
nal components, and internal MOSFETs under overload
conditions.
Input Capacitor Selection
Capacitor ESR is a major contributor to input ripple in
high-frequency DC-DC converters. Ordinary aluminum-
electrolytic capacitors have high ESR and should be
avoided. Low-ESR tantalum or polymer capacitors are
better and provide a compact solution for space-con-
strained surface-mount designs. Ceramic capacitors
have the lowest overall ESR.
The input filter capacitor reduces peak currents and
noise at the input voltage source. Connect a low-ESR
bulk capacitor (2.2µF to 10µF) to the input. Select this
bulk capacitor to meet the input ripple requirements
and voltage rating rather than capacitance value. Use
the following equation to calculate the maximum RMS
input current:
Applications Information
I
OUT
I
=
× V
×(V − V
)
Setting the Output Voltage
RMS
OUT
IN
OUT
V
IN
Using a DAC (MAX8506/MAX8507)
The MAX8506/MAX8507 are optimized for highest sys-
tem efficiency when applying power to a linear PA in
CDMA handsets. When transmitting at less than full
power, the supply voltage to the PA is lowered in many
steps from 3.4V to as low as 0.4V to greatly reduce bat-
tery current (see the Typical Application Circuits). The
use of DC-DC converters such as the MAX8506/
MAX8507 dramatically extends talk time in these appli-
cations.
Compensation, Stability, and
Output Capacitor
The MAX8506/MAX8507/MAX8508 are externally com-
pensated by placing a resistor and a capacitor (see the
Typical Application Circuits, R and C ) in series from
C
C
COMP to GND. An additional capacitor (C ) may be
f
required from COMP to GND if high-ESR output capaci-
tors are used. The C capacitor integrates the current
C
from the transimpedance amplifier, averaging output
8
_______________________________________________________________________________________
PWM Step-Down DC-DC Converters with 75mΩ
Bypass FET for WCDMA and cdmaOne Handsets
Table 1. Suggested Inductors
PART
NUMBER
INDUCTANCE
(µH)
SATURATION
CURRENT (A)
SUPPLIER
ESR (mΩ)
DIMENSIONS (mm)
Murata
LQH32C-53
CDRH2D11
LBLQ2016
D312C
4.7
4.7
4.7
4.7
150
135
250
200
0.650
0.500
0.210
0.790
2.5 x 3.2 x 1.7
3.2 x 3.2 x 1.2
1.6 x 2.0 x 1.6
3.6 x 3.6 x 1.2
Sumida
Taiyo Yuden
TOKO
capacitor ripple. This sets the device speed for transient
response and allows the use of small ceramic output
capacitors because the phase-shifted capacitor ripple
does not disturb the current-regulation loop. The resistor
sets the proportional gain of the output error voltage by
PC Board Layout and Routing
Table 2. Component Suppliers
SUPPLIER
PHONE
WEBSITE
Murata
770-436-1300
847-956-0666
408-573-4150
847-297-0070
www.murata.com
www.sumida.com
www.t-yuden.com
www.tokoam.com
a factor of g x R . Increasing this resistor also increas-
m
C
Sumida
es the sensitivity of the control loop to output ripple.
Taiyo Yuden
TOKO
The resistor and capacitor set a compensation zero that
defines the system’s transient response. The load cre-
ates a dynamic pole, shifting in frequency with changes
in load. As the load decreases, the pole frequency
shifts to the left. System stability requires that the com-
pensation zero must be placed to ensure adequate
phase margin (at least 30° at unity gain). With a 4.7µF
High switching frequencies and large peak currents
make PC board layout a very important part of design.
Good design minimizes EMI, noise on the feedback
paths, and voltage gradients in the ground plane, all of
which can result in instability or regulation errors.
Connect the inductor, input filter capacitor, and output fil-
ter capacitor as close together as possible and keep their
traces short, direct, and wide. The external voltage- feed-
back network should be very close to the FB pin, within
0.2in (5mm). Keep noisy traces, such as those from the
LX pin, away from the voltage-feedback network. Position
the bypass capacitors as close as possible to their
respective supply and ground pins to minimize noise cou-
pling. For optimum performance, place input and output
capacitors as close to the device as possible. Connect
GND directly under the IC to the exposed paddle. Refer
to the MAX8506 evaluation kit for an example PC board
layout and routing scheme.
output capacitor, the recommended C and R for the
C
C
MAX8506 are 1500pF and 10kΩ, respectively. This pro-
vides adequate phase margin over the entire output
voltage and load range and optimizes the output-
voltage settling time for REFIN dynamic control. See the
Typical Application Circuits for recommended C and
C
R values for the MAX8507 and MAX8508.
C
Inductor Selection
A 4µH to 6µH inductor is recommended for most appli-
cations. For best efficiency, the inductor’s DC resistance
should be <400mΩ. Saturation current (I
) should be
SAT
greater than the maximum DC load at the PA’s supply
plus half the inductor current ripple. Two-step V
CC
applications typically require very small inductors with
in the 200mA to 300mA region. See Tables 1 and 2
I
SAT
for recommended inductors and suppliers.
_______________________________________________________________________________________
9
PWM Step-Down DC-DC Converters with 75mΩ
Bypass FET for WCDMA and cdmaOne Handsets
Typical Application Circuits (MAX8508) (continued)
OUTPUT
0.75V TO 3.4V OR V
INPUT
2.6V TO 5.5V
4.7µH
BATT
4.7µF
2.2µF
BATTP
LX
BATT
OUT
MAX8508
0.075Ω
SKIP
SHDN
0.4Ω
0.3Ω
REF
CURRENT-
LIMIT
CONTROL
REF
PWM
0.22µF
R1
R2
1MHz
OSC
FB
HP
0.75V
PGND
GND
COMP
R
C
5.6kΩ
C
C
C
f
2700pF
100pF
Pin Configurations
TOP VIEW
16 15 14 13
16 15 14 13
SHDN
GND
1
2
3
4
SHDN
GND
REF
1
2
3
4
12 OUT
12 OUT
11 BATT
10 BATTP
11 BATT
10 BATTP
MAX8506
MAX8507
MAX8508
REF
REFIN
9
LX
FB
9
LX
5
6
7
8
5
6
7
8
THIN QFN
4mm x 4mm
THIN QFN
4mm x 4mm
Chip Information
TRANSISTOR COUNT: 2020
PROCESS: BiCMOS
10 ______________________________________________________________________________________
PWM Step-Down DC-DC Converters with 75mΩ
Bypass FET for WCDMA and cdmaOne Handsets
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
1
21-0139
B
2
PACKAGE OUTLINE
12,16,20,24L QFN THIN, 4x4x0.8 mm
2
21-0139
B
2
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.
This datasheet has been download from:
www.datasheetcatalog.com
Datasheets for electronics components.
相关型号:
MAX8508ETE+
Switching Regulator, Current-mode, 3.2A, 1200kHz Switching Freq-Max, BICMOS, PDSO16, 4 X 4 MM, 0.80 MM HEIGHT, MO-220, TQFN-16
MAXIM
MAX8508ETE+T
Switching Regulator, Current-mode, 3.2A, 1200kHz Switching Freq-Max, BICMOS, PDSO16, 4 X 4 MM, 0.80 MM HEIGHT, MO-220, TQFN-16
MAXIM
MAX8508ETE-T
Switching Regulator, Current-mode, 3.2A, 1200kHz Switching Freq-Max, BICMOS, PDSO16, 4 X 4 MM, 0.80 MM HEIGHT, MO-220, TQFN-16
MAXIM
MAX850CSA
Switched Capacitor Regulator, 0.005A, 100kHz Switching Freq-Max, CMOS, PDSO8, 0.150 INCH, PLASTIC, SOIC-8
MAXIM
MAX850CSA+T
Switched Capacitor Regulator, 100kHz Switching Freq-Max, CMOS, PDSO8, 0.150 INCH, PLASTIC, SOIC-8
MAXIM
MAX850CSA-T
Switched Capacitor Regulator, 100kHz Switching Freq-Max, CMOS, PDSO8, 0.150 INCH, PLASTIC, SOIC-8
MAXIM
MAX850ESA+
Switched Capacitor Regulator, 0.005A, 120kHz Switching Freq-Max, CMOS, PDSO8, PLASTIC, SOP-8
MAXIM
MAX850ESA+T
Switched Capacitor Regulator, 0.005A, 100kHz Switching Freq-Max, CMOS, PDSO8, PLASTIC, SOP-8
MAXIM
©2020 ICPDF网 联系我们和版权申明