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PDF MAX8597 Data sheet ( Hoja de datos )
| Número de pieza | MAX8597 | |
| Descripción | Low-Dropout Wide-Input-Voltage Step-Down Controllers | |
| Fabricantes | Maxim Integrated Products | |
| Logotipo |  |
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19-3505; Rev 0; 11/04
EVAALVUAAILTAIOBNLEKIT
www.DataSheet4U.com
Low-Dropout, Wide-Input-Voltage,
Step-Down Controllers
General Description
The MAX8597/MAX8598/MAX8599 voltage-mode PWM
step-down controllers are designed to operate from a
4.5V to 28V input supply and generate output voltages
down to 0.6V. A proprietary switching algorithm stretch-
es the duty cycle to >99.5% for low-dropout design.
Unlike conventional step-down regulators using a p-
channel high-side MOSFET to achieve high duty cycle,
the MAX8597/MAX8598/MAX8599 drive n-channel
MOSFETs resulting in high efficiency and high-current-
capability designs.
The MAX8597 is available in a 20-pin thin QFN pack-
age and is designed for applications that use an analog
signal to control the output voltage with an adjustable
offset, such as DC fan-speed control. This is achieved
with an internal uncommitted operational amplifier. The
MAX8597 is also targeted for tracking output-voltage
applications for chipsets, ASIC and DSP cores, and I/O
supplies. The MAX8598/MAX8599 are available in a 16-
pin thin QFN package and do not have the uncommitted
operational amplifier, reference input, and reference out-
put, but offer an open-drain, power-OK output.
The MAX8597/MAX8598/MAX8599 allow startup with
prebias voltage on the output for applications where a
backup supply or a tracking device may charge the
output capacitor before the MAX8597/MAX8598/
MAX8599 are enabled. In addition, the MAX8599 fea-
tures output overvoltage protection.
These controllers also feature lossless high-side peak
inductor current sensing, adjustable current limit, and
hiccup-mode short-circuit protection. Switching fre-
quency is set with an external resistor from 200kHz to
1.4MHz. This wide frequency range combined with a
wide-bandwidth error amplifier enables the loop com-
pensation scheme to give the user ample flexibility to
optimize for cost, size, and efficiency.
Applications
Nonisolated Power Modules
Variable-Speed DC Fan Power Supplies
(MAX8597)
Tracking Power Supplies (MAX8597)
Chipset Power Supplies
Features
♦ Low Dropout with >99.5% Duty Cycle
♦ Lossless High-Side Current Limit
♦ Wide 4.5V to 28V Input Range
♦ Dynamic Output Voltage Adjustment with
Adjustable Offset (MAX8597)
♦ Remote Voltage Sensing for Both Positive and
Negative Rails (MAX8597)
♦ Tracking Output Through REFIN (MAX8597)
♦ Adjustable Switching Frequency from 200kHz to
1.4MHz
♦ Adjustable Soft-Start
♦ Prebias Startup
♦ Enable and Power-OK (MAX8598/MAX8599) for
Flexible Sequencing
♦ 25MHz Error Amplifier
♦ Adjustable Hiccup Current Limit for Output
Short-Circuit Protection
♦ Output Overvoltage Protection (MAX8599)
♦ Small, Low-Profile Thin QFN Package
Ordering Information
PART
TEMP RANGE PIN-PACKAGE
MAX8597ETP+
-40°C to +85°C
20 Thin QFN 4mm x 4mm
(T2044-3)
MAX8598ETE+
-40°C to +85°C
16 Thin QFN 4mm x 4mm
(T1644-4)
MAX8599ETE+
-40°C to +85°C
16 Thin QFN 4mm x 4mm
(T1644-4)
+Denotes lead-free package.
Pin Configurations
TOP VIEW
15 14 13 12 11
ILIM 16
10 VL
FREQ 17
9 V+
AOUT 18
MAX8597
8 REFOUT
AIN- 19
7 EN
AIN+ 20
6 COMP
1234 5
THIN QFN
4mm x 4mm
Pin Configurations 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.
1 page  
www.DataSheet4U.com
Low-Dropout, Wide-Input-Voltage,
Step-Down Controllers
ELECTRICAL CHARACTERISTICS (continued)
(VV+ = VVL = VAVL = VEN = VREFIN = 5V, VBST = 6V, VLX = 1V, CVL = 4.7µF, CREFOUT = 1µF, VAIN- = VAOUT, VAIN+ = 2.5V, VILIM =
VLX - 0.2V, VFB = 0.65V, GND = PGND = 0V, CSS = 0.01µF, RFREQ = 20kΩ, TA = -40°C to +85°C, typical values are at TA = +25°C,
unless otherwise noted.) (Note 1)
PARAMETER
CONDITIONS
FREQUENCY
Frequency
DH Minimum Off-Time
RFREQ = 100kΩ
RFREQ = 20.0kΩ
RFREQ = 14.3kΩ
DH Minimum On-Time
FB ERROR AMPLIFIER
FB Input Bias Current
FB Input Voltage Set Point
Over load and line
FB Offset Error
VREFIN = 1.25V and 2.5V, measured with respect to REFIN
Error-Amp Open-Loop Voltage
Gain
VCOMP = 1.2V to 2.4V
UNCOMMITTED OPERATIONAL AMPLIFIER (MAX8597 only)
Output Voltage Swing High
VAIN+ = 2.5V, VAIN- = (VAIN+ - 100mV), ISOURCE = 100µA
Output Voltage Swing Low
Input Offset Voltage
Input Common-Mode Range
(CMVR)
DRIVERS
DH On-Resistance in Low State
DH On-Resistance in High State
DL On-Resistance in Low State
DL On-Resistance in High State
BST Bias Current
LX Bias Current
BST/LX Leakage Current
LOGIC INPUTS (EN)
Input Low Level
Input High Level
Input Bias Current
REFIN INPUT (MAX8597 only)
REFIN Input Voltage Range
VAIN+ = 2.5V, VAIN- = (VAIN+ + 100mV), ISINK = 100µA
VCM = 1.25V and 2.5V
VBST - VLX = 5V
VBST - VLX = 5V
VVL = VV+ = 5V
VVL = VV+ = 5V
VBST = 33V, VLX = 28V, VEN = 0V
VBST = 33V, VLX = 28V, VEN = 0V
VBST = VLX = 28V, VEN = 0V
4.5V < VVL = VV+ = VAVL < 5.5V
4.5V < VVL = VV+ = VAVL < 5.5V
VVL = VV+ = VAVL = 5.5V, VEN = 0 to 5.5V
REFIN Dual-Mode Threshold
REFIN Input Bias Current
VREFIN = 1.25V or 2.5V
MIN TYP MAX UNITS
140
800
1100
180
240
1200
1700
230
140
kHz
ns
ns
0.591
+20
72
150
0.606
-20
nA
V
mV
dB
VAVL -
20mV
-3
+0.50
2.4
-1
0
VAVL -
1.0
-250
20
+3
VAVL -
2.0
V
mV
mV
V
2.5
3.3
1.0
3.5
520
-520
50
Ω
Ω
Ω
Ω
µA
µA
µA
0.8 V
V
+1 µA
2.75
VAVL -
0.5
+250
V
V
nA
_______________________________________________________________________________________ 5
5 Page 
www.DataSheet4U.com
Low-Dropout, Wide-Input-Voltage,
Step-Down Controllers
Pin Description (continued)
PIN
MAX8597 MAX8598/
MAX8599
17 15
18 —
19 —
20 —
— 16
——
NAME
FREQ
AOUT
AIN-
AIN+
POK
EP
FUNCTION
Frequency Adjust Input. Connect a resistor from FREQ to GND to set the switching frequency.
The range of the FREQ resistor is 14.3kΩ to 100kΩ (corresponding to 1400kHz to 200kHz).
Output of the Uncommitted Operational Amplifier. AOUT is high impedance during
undervoltage lockout.
Inverting Input of the Uncommitted Operational Amplifier
Noninverting Input of the Uncommitted Operational Amplifier
Power-OK Output. POK is an open-drain output that goes high impedance when the regulator
output is greater than 88% of the regulation threshold. POK is low during shutdown.
Exposed Paddle. Connect to analog ground plane for improved thermal performance.
Detailed Description
The MAX8597/MAX8598/MAX8599 voltage-mode PWM
step-down controllers are designed to operate from
4.5V to 28V input and generate output voltages down to
0.6V. A proprietary switching algorithm stretches the
duty cycle to >99.5% for low-dropout design. Unlike
conventional step-down regulators using a p-channel
high-side MOSFET to achieve high duty cycle, the
MAX8597/MAX8598/MAX8599 drive n-channel
MOSFETs permitting high efficiency and high-current
designs.
The MAX8597 is available in a 20-pin thin QFN pack-
age and is designed for applications that use an ana-
log signal to control the output voltage with adjustable
offset, such as DC fan speed control. For example, a
12VDC fan can be driven from 6V to 12V with 12V input
power source depending on the system’s cooling
requirement to minimize fan noise and power consump-
tion. This is achieved with an internal uncommitted
operational amplifier. With the addition of an external
RC filter, a PWM input can also be used to control the
output voltage. The MAX8597 also generates a tracking
output for chipsets, ASICs, and DSP where core and
I/O supplies are split and require tracking. In applica-
tions where tighter output tolerance is required, the
MAX8597 output can be set by an external precision
reference source feeding to REFIN. The MAX8598/
MAX8599 are available in a 16-pin thin QFN package
and do not have the uncommitted operational amplifier,
reference input, and reference output, but offer a power-
OK output (POK). With the enable input and POK out-
put, the MAX8598/MAX8599 can easily be configured to
have power sequencing of multiple supply rails.
The MAX8597/MAX8598/MAX8599 allow startup with
prebias voltage on the output for applications where a
backup supply or a tracking device may charge the
output capacitor before the MAX8597/MAX8598/
MAX8599 are enabled. The MAX8599 has output over-
voltage protection.
These controllers feature lossless high-side peak
inductor current sensing, adjustable current limit, and
hiccup-mode short-circuit protection. Switching fre-
quency is set with an external resistor from 200kHz to
1.4MHz. This wide frequency range combined with a
wide-bandwidth error amplifier enable the loop-com-
pensation scheme to give the user ample flexibility to
optimize for cost, size, and efficiency.
DC-DC Controller
The MAX8597/MAX8598/MAX8599 step-down DC-DC
controllers use a PWM voltage-mode control scheme. An
internal high-bandwidth (25MHz) operational amplifier is
used as an error amplifier to regulate the output voltage.
The output voltage is sensed and compared with an inter-
nal 0.6V reference or REFIN (MAX8597) to generate an
error signal. The error signal is then compared with a
fixed-frequency ramp by a PWM comparator to give the
appropriate duty cycle to maintain output voltage regula-
tion. The high-side MOSFET turns on at the rising edge of
the internal clock 20ns after DL (the low-side MOSFET
gate drive) goes low. The high-side MOSFET turns off
once the internal ramp voltage reaches the error-amplifier
output voltage. The process repeats for every clock
cycle. During the high-side MOSFET on-time, current
flows from the input through the inductor to the output
capacitor and load. At the moment the high-side MOS-
FET turns off, the energy stored in the inductor during the
on-time is released to support the load as the inductor
______________________________________________________________________________________ 11
11 Page | ||
| Páginas | Total 24 Páginas | |
| PDF Descargar | [ Datasheet MAX8597.PDF ] | |
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