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PDF MAX1846 Data sheet ( Hoja de datos )
| Número de pieza | MAX1846 | |
| Descripción | High-Efficiency / Current-Mode / Inverting PWM Controller | |
| Fabricantes | Maxim Integrated | |
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19-2091; Rev 0; 8/01
High-Efficiency, Current-Mode,
Inverting PWM Controller
General Description
MAX1846/MAX1847 high-efficiency PWM inverting con-
trollers allow designers to implement compact, low-
noise, negative-output DC-DC converters for telecom
and networking applications. Both devices operate
from +3V to +16.5V input and generate -2V to -200V
output. To minimize switching noise, both devices fea-
ture a current-mode, constant-frequency PWM control
scheme. The operating frequency can be set from
100kHz to 500kHz through a resistor.
The MAX1846 is available in an ultra-compact 10-pin
µMAX package. Operation at high frequency, compati-
bility with ceramic capacitors, and inverting topology
without transformers allow for a compact design.
Compatibility with electrolytic capacitors and flexibility
to operate down to 100kHz allow users to minimize the
cost of external components. The high-current output
drivers are designed to drive a P-channel MOSFET and
allow the converter to deliver up to 30W.
The MAX1847 features clock synchronization and shut-
down functions. The MAX1847 can also be configured
to operate as an inverting flyback controller with an N-
channel MOSFET and a transformer to deliver up to
70W. The MAX1847 is available in a 16-pin QSOP
package.
Current-mode control simplifies compensation and pro-
vides good transient response. Accurate current-mode
control and over current protection are achieved
through low-side current sensing.
Applications
Cellular Base Stations
Networking Equipment
Optical Networking Equipment
SLIC Supplies
CO DSL Line Driver Supplies
Industrial Power Supplies
Automotive Electronic Power Supplies
Servers
Features
o 90% Efficiency
o +3.0V to +16.5V Input Range
o -2V to -200V Output
o Drives High-Side P-Channel MOSFET
o 100kHz to 500kHz Switching Frequency
o Current-Mode, PWM Control
o Internal Soft-Start
o Electrolytic or Ceramic Output Capacitor
o The MAX1847 also offers:
Synchronization to External Clock
Shutdown
N-Channel Inverting Flyback Option
PART
MAX1846EUB
MAX1847EEE
Ordering Information
TEMP. RANGE
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
10 µMAX
16 QSOP
Typical Operating Circuit
POSITIVE
VIN
VL IN
EXT
MAX1846
MAX1847
COMP
CS
FREQ
PGND
P NEGATIVE
VOUT
REF
GND
FB
Pin Configurations appear 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  
High-Efficiency, Current-Mode,
Inverting PWM Controller
ELECTRICAL CHARACTERISTICS (continued)
(VSHDN = VIN = +12V, SYNC = GND, PGND = GND, RFREQ = 147kΩ ±1%, CVL = 0.47µF, CREF = 0.1µF, TA = -40°C to +85°C,
unless otherwise noted.) (Note 3)
PARAMETER
CONDITIONS
POL, SYNC Input Current
POL, SYNC = GND or VL
SHDN Input Current
EXT OUTPUT
VSHDN = +5V or GND
VSHDN = +16.5V
EXT On-Resistance
EXT high or low, IEXT = 100mA, VIN = +5V
EXT high or low, IEXT = 100mA, VIN = +3V
Note 3: Parameters to -40°C are guaranteed by design and characterization.
MIN MAX UNITS
40 µA
-12 0
µA
6
7.5
Ω
12
Typical Operating Characteristics
(Circuit references are from Table 1 in the Main Application Circuits section, CVL = 0.47µF, CREF = 0.1µF, TA = +25°C, unless otherwise
noted.)
EFFICIENCY vs. LOAD CURRENT
100
90
80 VIN = 5V
70
60
50 VIN = 16.5V
40
30
20
10
APPLICATION CIRCUIT A
0
1 10 100
VOUT = -5V
1000 10,000
LOAD CURRENT (mA)
EFFICIENCY vs. LOAD CURRENT
100
VIN = 5V
90
80
70 VIN = 3.3V
60 VIN = 3V
50
40
30
20
10
APPLICATION CIRCUIT B
0
1 10 100
VOUT = -12V
1000 10,000
LOAD CURRENT (mA)
EFFICIENCY vs. LOAD CURRENT
100
90
80 VIN = 12V
70
60 VIN = 16.5V
50
40
30
20
10
0 APPLICATION CIRCUIT C
1 10
VOUT = -48V
100 1000
LOAD CURRENT (mA)
OUTPUT VOLTAGE LOAD REGULATION
-11.90
-11.92
-11.94
-11.96
-11.98
-12.00
-12.02
-12.04
-12.06
-12.08
APPLICATION CIRCUIT B
-12.10
0 100 200 300
VIN = 5V
400 500
LOAD CURRENT (mA)
600
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
0
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
VFB = -0.1V
2 4 6 8 10 12 14 16
VIN (V)
REFERENCE VOLTAGE
vs. TEMPERATURE
1.262
1.258
1.254
1.250
1.246
1.242
1.238
-40 -20
0 20 40 60
TEMPERATURE (°C)
80 100
_______________________________________________________________________________________ 5
5 Page 
High-Efficiency, Current-Mode,
Inverting PWM Controller
Detailed Description
The MAX1846/MAX1847 current-mode PWM controller
use an inverting topology that is ideal for generating
output voltages from -2V to -200V. Features include
shutdown, adjustable internal operating frequency or
synchronization to an external clock, soft-start,
adjustable current limit, and a wide (+3V to +16.5V)
input range.
PWM Controller
The architecture of the MAX1846/MAX1847 current-
mode PWM controller is a Bi-CMOS multi-input system
that simultaneously processes the output-error signal,
the current-sense signal, and a slope-compensation
ramp (Functional Diagram). Slope compensation pre-
vents subharmonic oscillation, a potential result in cur-
rent-mode regulators operating at greater than 50%
duty cycle. The controller uses fixed-frequency, cur-
rent-mode operation where the duty ratio is set by the
input-to-output voltage ratio. The current-mode feed-
back loop regulates peak inductor current as a function
of the output error signal.
Internal Regulator
The MAX1846/MAX1847 incorporate an internal low-
dropout regulator (LDO). This LDO has a 4.25V output
and powers all MAX1846/MAX1847 functions (exclud-
ing EXT) for the primary purpose of stabilizing the per-
formance of the IC over a wide input voltage range
(+3V to +16.5V). The input to this regulator is connect-
ed to IN, and the dropout voltage is typically 100mV, so
that when VIN is less than 4.35V, VL is typically VIN
minus 100mV. When the LDO is in dropout, the
MAX1846/MAX1847 still operate with VIN as low as 3V.
For best performance, it is recommended to connect
VL to IN when the input supply is less than 4.5V.
Undervoltage Lockout
The MAX1846/MAX1847 have an undervoltage lockout
circuit that monitors the voltage at VL. If VL falls below
the UVLO threshold (2.8V typ), the control logic turns the
P-channel FET off (EXT high impedance). The rest of the
IC circuitry is still powered and operating. When VL
increases to 60mV above the UVLO threshold, the IC
resumes operation from a start up condition (soft-start).
Soft-Start
The MAX1846/MAX1847 feature a “digital” soft-start
that is preset and requires no external capacitor. Upon
startup, the FB threshold decrements from the refer-
ence voltage to 0 in 64 steps over 1024 cycles of fOSC
or fSYNC. See the Typical Operating Characteristics for
a scope picture of the soft-start operation. Soft-start is
implemented: 1) when power is first applied to the IC,
2) when exiting shutdown with power already applied,
and 3) when exiting undervoltage lockout.
Shutdown (MAX1847 only)
The MAX1847 shuts down to reduce the supply current
to 10µA when SHDN is low. In this mode, the internal ref-
erence, error amplifier, comparators, and biasing circuit-
ry turn off. The EXT output becomes high impedance
and the external pullup resistor connected to EXT pulls
VEXT to VIN, turning off the P-channel MOSFET. When in
shutdown mode, the converter’s output goes to 0.
Frequency Synchronization
(MAX1847 only)
The MAX1847 is capable of synchronizing its switching
frequency with an external clock source. Drive SYNC
with a logic-level clock input signal to synchronize the
MAX1847. A switching cycle starts on the rising edge
of the signal applied to SYNC. Note that the frequency
of the signal applied to SYNC must be higher than the
default frequency set by RFREQ. This is required so that
the internal clock does not start a switching cycle pre-
maturely. If SYNC is inactive for an entire clock cycle of
the internal oscillator, the internal oscillator takes over
the switching operation. Choose RFREQ such that fOSC
= 0.9 ✕ fSYNC.
EXT Polarity (MAX1847 only)
The MAX1847 features an option to utilize an N-channel
MOSFET configuration, rather than the typical P-chan-
nel MOSFET configuration (Figure 1). In order to drive
the different polarities of these MOSFETs, the MAX1847
is capable of reversing the phase of EXT by 180
degrees. When driving a P-channel MOSFET, connect
POL to GND. When driving an N-Channel MOSFET,
connect POL to VL. These POL connections ensure the
proper polarity for EXT. For design guidance in regard
to this application, refer to the MAX1856 data sheet.
Design Procedure
Initial Specifications
In order to start the design procedure, a few parameters
must be identified: the minimum input voltage expected
(VIN(MIN)), the maximum input voltage expected
(VIN(MAX)), the desired output voltage (VOUT), and the
expected maximum load current (ILOAD).
Calculate the Equivalent Load Resistance
This is a simple calculation used to shorten the verifica-
tion equations:
RLOAD = VOUT / ILOAD
______________________________________________________________________________________ 11
11 Page | ||
| Páginas | Total 20 Páginas | |
| PDF Descargar | [ Datasheet MAX1846.PDF ] | |
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