Datasheet

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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 -500mV to

-200V output. To minimize switching noise, both devices

feature 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, com-

patibility with ceramic capacitors, and inverting topol-

ogy 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

● Servers

● VOIP Supplies

Features

● 90% Efficiency

● +3.0V to +16.5V Input Range

● -500mV to -200V Output

● Drives High-Side P-Channel MOSFET

● 100kHz to 500kHz Switching Frequency

● Current-Mode, PWM Control

● Internal Soft-Start

● Electrolytic or Ceramic Output Capacitor

● The MAX1847 also offers:

Synchronization to External Clock Shutdown

N-Channel Inverting Flyback Option

µMAX is a registered trademark of Maxim Integrated Products, Inc.

Pin Configurations appear at end of data sheet.

19-2091; Rev 3; 3/14

+Denotes a lead(Pb)-free/RoHS-compliant package.

PART TEMP RANGE PIN-PACKAGE

MAX1846EUB -40°C to +85°C 10 µMAX

MAX1846EUB+ -40°C to +85°C 10 µMAX

MAX1847EEE -40°C to +85°C 16 QSOP

MAX1847EEE+ -40°C to +85°C 16 QSOP

MAX1846

MAX1847

VL IN

COMP

FREQ

REF

GND

PGND

EXT

POSITIVE

NEGATIVE

OUT

MAX1846–MAX1847 High-Efficiency, Current-Mode,

Inverting PWM Controller

Typical Operating Circuit

Ordering Information

EVALUATION KIT AVAILABLE

Summary of content (20 pages)

PAGE 1
EVALUATION KIT AVAILABLE MAX1846–MAX1847 High-Efficiency, Current-Mode, Inverting PWM Controller General Description Features The MAX1846 is available in an ultra-compact 10-pin µMAX® package. Operation at high frequency, compatibility 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.
PAGE 2
MAX1846–MAX1847 High-Efficiency, Current-Mode, Inverting PWM Controller Absolute Maximum Ratings IN, SHDN to GND..................................................-0.3V to +20V PGND to GND.......................................................-0.3V to +0.3V VL to PGND for VIN ≤ 5.7V.........................-0.3V to (VIN + 0.3V) VL to PGND for VIN > 5.7V......................................-0.3V to +6V EXT to PGND..............................................-0.3V to (VIN + 0.3V) REF, COMP to GND.........
PAGE 3
MAX1846–MAX1847 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 = 0°C to +85°C, unless otherwise noted.
PAGE 4
MAX1846–MAX1847 High-Efficiency, Current-Mode, Inverting PWM Controller Electrical Characteristics (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 PWM CONTROLLER Operating Input Voltage Range UVLO Threshold FB Threshold FB Input Current Load Regulation Current Limit Threshold CONDITIONS VIN rising VIN falling MIN MAX UNITS 3.0 16.5 V 2.95 2.6 V No load -20 +20 mV VFB = -0.
PAGE 5
MAX1846–MAX1847 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 MIN POL, SYNC = GND or VL V SHDN = +5V or GND SHDN Input Current MAX UNITS 40 µA -12 0 V SHDN = +16.5V EXT OUTPUT EXT high or low, IEXT = 100mA, VIN = +5V EXT On-Resistance µA 6 7.
PAGE 6
MAX1846–MAX1847 High-Efficiency, Current-Mode, Inverting PWM Controller Typical Operating Characteristics (continued) (Circuit references are from Table 1 in the Main Application Circuits section, CVL = 0.47µF, CREF = 0.1°F, TA = +25°C, unless otherwise noted.) VL VOLTAGE vs. TEMPERATURE 4.300 4.27 4.26 1.250 VL (V) 4.260 VL (V) 4.220 4.24 4.180 1.245 4.23 4.140 100 200 300 400 500 IVL = 0 -40 -20 0 IREF (A) 10 8 VIN = 3V 6 4 14 OPERATING CURRENT (mA) VIN = 10V VIN = 16.
PAGE 7
MAX1846–MAX1847 High-Efficiency, Current-Mode, Inverting PWM Controller Typical Operating Characteristics (continued) (Circuit references are from Table 1 in the Main Application Circuits section, CVL = 0.47µF, CREF = 0.1°F, TA = +25°C, unless otherwise noted.
PAGE 8
MAX1846–MAX1847 High-Efficiency, Current-Mode, Inverting PWM Controller Pin Description MAX1846 PIN MAX1847 NAME FUNCTION Sets polarity of the EXT pin. Connect POL to GND to set EXT for use with an external PMOS high-side FET. Connect POL to VL to set EXT for use with an external NMOS lowside FET in transformer-based applications. — 1 POL 1 2 VL VL Low-Dropout Regulator. Connect 0.47µF ceramic capacitor from VL to GND. 2 3 FREQ Oscillator Frequency Set Input.
PAGE 9
MAX1846–MAX1847 High-Efficiency, Current-Mode, Inverting PWM Controller Typical Application Circuit 3 x 22µF 10V VIN +3V to +5.5V 22kΩ FDS6375 2 0.47µF 16 SHDN 10kΩ 150kΩ CS MAX1847 4 0.22µF EXT SYNC 220pF 3 5 VOUT -12V AT 400mA IN VL 8 CMSH5-40 15 COMP N.C. PGND 47µF 16V 10µH DO5022P-103 14 13 47µF 16V SANYO 16TPB47M 7, 9 0.02Ω 1W 12 R1 95.3kΩ 1% FREQ REF FB POL 1 GND 10, 11 6 1200pF R2 10.0kΩ 1% 0.1µF www.maximintegrated.
PAGE 10
MAX1846–MAX1847 High-Efficiency, Current-Mode, Inverting PWM Controller Functional Diagram IN EXT SHDN MAX1847 ONLY STARTUP CIRCUITRY PGND EXT DRIVER VL VL REGULATOR UNDERVOLTAGE LOCK OUT SYNC MAX1847 ONLY MAX1846 MAX1847 CONTROL CIRCUITRY POL OSCILLATOR FREQ ERROR COMPARATOR COMP CS FB GM SOFT-START CURRENTSENSE AMPLIFIER ERROR AMPLIFIER PGND X3.3 SLOPE COMP REF REFERENCE GND www.maximintegrated.
PAGE 11
MAX1846–MAX1847 Detailed Description The MAX1846/MAX1847 current-mode PWM controllers use an inverting topology that is ideal for generating output voltages from -500mV 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.
PAGE 12
MAX1846–MAX1847 High-Efficiency, Current-Mode, Inverting PWM Controller VIN +12V 12µF VP1-0190 25V 12.2µH 0.47µF 8 16 1 2 VL POL SYNC 0.033µF 270kΩ 150kΩ 3 5 COMP FREQ REF VOUT -48V AT 100mA IRLL2705 EXT CS MAX1847 4 CMR1U-02 15 IN SHDN 1:4 N.C. PGND GND FB 10, 11 14 470Ω 13 100pF 100V 7, 9 0.05Ω 0.5W 12µF 100V 383kΩ 1% 12 6 1800pF 10.0kΩ 1% 0.1µF Figure 1.
PAGE 13
MAX1846–MAX1847 High-Efficiency, Current-Mode, Inverting PWM Controller 2) Higher frequencies allow the use of smaller value (hence smaller size) inductors and capacitors. to the rate set by RFREQ. Choose RFREQ such that fOSC = 0.9 x fSYNC. 3) Higher frequencies consume more operating power both to operate the IC and to charge and discharge the gate at the external FET, which tends to reduce the efficiency at light loads.
PAGE 14
MAX1846–MAX1847 High-Efficiency, Current-Mode, Inverting PWM Controller tance as possible. For continuous inductor current, the power loss in the inductor resistance (PLR) is approximated by:  I  PLR ~ R L x  LOAD   I − D MAX  2 where RL is the inductor series resistance. Once the peak inductor current is calculated, the current sense resistor, RCS, is determined by: RCS = 85mV / ILPEAK For high peak inductor currents (>1A), Kelvin-sensing connections should be used to connect CS and PGND to RCS.
PAGE 15
MAX1846–MAX1847 The ESR-induced ripple usually dominates this last equation, so typically output capacitor selection is based mostly upon the capacitor's ESR, voltage rating, and ripple current rating. Use the following formula to determine the maximum ESR for a desired output ripple voltage (VRIPPLE-D): RESR = VRIPPLE-D / ILPP Select a capacitor with ESR rating less than RESR. The value of this capacitor is highly dependent on dielectric type, package size, and voltage rating.
PAGE 16
MAX1846–MAX1847 High-Efficiency, Current-Mode, Inverting PWM Controller Select the next smaller standard value of resistor and then calculate the compensation capacitor required to cancel out the output-capacitor-induced pole (POUT1) determined previously. C COMP = Maximum Output Power 1 The maximum output power that the MAX1846/MAX1847 can provide depends on the maximum input power available and the circuit's efficiency: 6.
PAGE 17
MAX1846–MAX1847 High-Efficiency, Current-Mode, Inverting PWM Controller Input Filter Capacitor PC Board Layout Guidelines The input capacitor (CIN) must provide the peak current into the inverter. This capacitor is selected the same way as the output capacitor (COUT). Under ideal conditions, the RMS current for the input capacitor is the same as the output capacitor.
PAGE 18
MAX1846–MAX1847 High-Efficiency, Current-Mode, Inverting PWM Controller Table 1. Component List for Main Application Circuits A B C D Input (V) CIRCUIT ID 12 3 to 5.5 12 12 Output (V) -5 -12 -48 -72 Output (A) CCOMP (µF) CIN (µF) 2 0.4 0.1 0.1 0.047 0.22 0.1 0.068 10 3 x 10 3 x 22 10 2 x 100 2 x 47 39 39 390 1200 1000 1000 R1 (kW) (1%) 40.2 95.3 383 576 R2 (kW) (1%) 10 10 10 10 RCOMP (kΩ) 8.2 10 220 470 0.02 0.02 0.05 0.
PAGE 19
MAX1846–MAX1847 High-Efficiency, Current-Mode, Inverting PWM Controller Chip Information Pin Configurations PROCESS: BiCMOS TOP VIEW VL 1 FREQ 2 COMP 3 REF 4 FB 5 + 10 IN MAX1846 µMAX POL 1 + 16 SYNC 15 IN VL 2 9 EXT 8 CS 7 PGND COMP 4 6 GND 14 EXT FREQ 3 MAX1847 12 PGND FB 6 11 GND N.C. 7 10 GND SHDN 8 9 QSOP www.maximintegrated.com 13 CS REF 5 N.C. Package Information For the latest package outline information and land patterns (footprints), go to www.
PAGE 20
MAX1846–MAX1847 High-Efficiency, Current-Mode, Inverting PWM Controller Revision History REVISION NUMBER REVISION DATE PAGES CHANGED 2 9/10 Added equation in the Determining the Compensation Component Values section 16 3 3/14 Removed automotive application from the Applications section 1 DESCRIPTION For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com.