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ADP1877
Dual Output Synchronous Buck PWM Controller
Dual Output Synchronous Buck
PWM Controller ADP1877
FEATURES
Input voltage range: 2.75 V to 14.5 V
Output voltage range: 0.6 V to 90% VIN
Maximum output current greater than 25 A per channel
Programmable frequency: 200 kHz to 1.5 MHz
Flex-Mode architecture with integrated drivers
180° phase shift minimizes input ripple current and required
input capacitance
±0.85% output voltage accuracy −40°C to +85°C
Integrated boost diodes
Pulse skip high efficiency mode under light load
Power good with internal pull-up resistor
Overvoltage and overcurrent limit protection
Thermal overload protection
Input undervoltage lockout (UVLO)
Externally adjustable soft start, slope compensation and
current sense gain
Independent precision enable inputs
Synchronization input
Suitable for any output capacitors
Available in 32-lead 5 mm × 5 mm LFCSP
APPLICATIONS
Set top boxes
Printers
Communication infrastructure
Distributor power dc systems
Industrial and instrumentation
GENERAL DESCRIPTION The ADP1877 is a Flex-Mode™ (proprietary architecture of
Analog Devices, Inc.), dual-channel, step-down switching
controller with integrated drivers that drive N-channel
synchronous power MOSFETs. The two PWM outputs are
phase shifted 180°, which reduces the input RMS current, thus
minimizing required input capacitance.
The boost diodes are built into the ADP1877, thus lowering the
overall system cost and component count. The ADP1877 can
be set to operate in pulse skip high efficiency mode under light
load or in PWM continuous conduction mode.
The ADP1877 includes externally adjustable soft start, output
overvoltage protection, externally adjustable current limit,
power good, and a programmable oscillator frequency that
ranges from 200 kHz to 1.5 MHz. The ADP1877 provides an
output voltage accuracy of ±0.85% from −40°C to +85°C and
±1.5% from −40°C to 125°C in junction temperature. This part
can be powered from a 2.75 V to 14.5 V supply, operates over
the −40oC to +125oC junction temperature range, and is availa-
ble in a 32-lead 5 mm × 5 mm LFCSP package.
RAMP1
RCSG1
RTOP1
RBOT1
RCSG2
RTOP2L2
VOUT1
VOUT2
VIN
RBOT2
RRAMP2Figure 1. Typical Operation Circuit
100LOAD (A)
Figure 2. Efficiency Plot of Figure 42, 20 A Output
TABLE OF CONTENTS Features .............................................................................................. 1
Applications ....................................................................................... 1
General Description ......................................................................... 1
Revision History ............................................................................... 2
Specifications ..................................................................................... 3
Absolute Maximum Ratings ............................................................ 6
ESD Caution .................................................................................. 6
Simplified Block Diagram ............................................................... 7
Pin Configuration and Function Descriptions ............................. 8
Typical Performance Characteristics ........................................... 10
Theory of Operation ...................................................................... 13
Control Architecture .................................................................. 13
Oscillator Frequency .................................................................. 13
Mode of Operation ..................................................................... 14
Synchronization .......................................................................... 14
Soft Start ...................................................................................... 14
Synchronous Rectifier and Dead Time ................................... 15
Input Undervoltage Lockout ..................................................... 15
Internal Linear Regulator .......................................................... 15
Overvoltage Protection .............................................................. 15
Power Good ................................................................................. 15
Short-Circuit and Current-Limit Protection .......................... 16
Shutdown Control ...................................................................... 16
Thermal Overload Protection ................................................... 16
Applications Information .............................................................. 17
Setting the Output Voltage ........................................................ 17
Soft Start ...................................................................................... 17
Setting the Current Limit .......................................................... 17
Accurate Current-Limit Sensing .............................................. 18
Setting the Slope Compensation .............................................. 18
Setting the Current Sense Gain ................................................ 18
Input Capacitor Selection .......................................................... 19
Input Filter ................................................................................... 19
Boost Capacitor Selection ......................................................... 20
Inductor Selection ...................................................................... 20
Output Capacitor Selection ....................................................... 20
MOSFET Selection ..................................................................... 21
Loop Compensation .................................................................. 22
Switching Noise and Overshoot Reduction ............................ 23
Voltage Tracking ......................................................................... 23
Coincident Tracking .................................................................. 23
Ratiometric Tracking ................................................................. 24
PCB Layout Guideline ................................................................... 25
MOSFETs, Input Bulk Capacitor, and Bypass Capacitor ...... 25
High Current and Current Sense Paths ................................... 25
Signal Paths ................................................................................. 25
PGND Plane ................................................................................ 25
Feedback and Current-Limit Sense Paths ............................... 25
Switch Node ................................................................................ 26
Gate Driver Paths ....................................................................... 26
Output Capacitors ...................................................................... 26
Typical Operating Circuits ............................................................ 27
Outline Dimensions ....................................................................... 31
Ordering Guide .......................................................................... 31
REVISION HISTORY
4/12—Rev. C to Rev. D Changes to Setting the Current Sense Gain Section .................. 18
Updated Outline Dimensions ....................................................... 31
4/10—Rev. B to Rev. C Changes to Features and General Description ............................. 1
Changes to Quiescent Current Parameter and FB to TRK Offset
Voltage Parameter, Table 1 .............................................................. 3
Changes to Theory of Operation Section .................................... 13
Changes to Setting the Slope Compensation Section ................ 18
11/09—Rev. A to Rev. B
9/09—Rev. 0 to Rev. A Changes to Features Section, General Description Section, and
Figure 2 ............................................................................................... 1
Changes to Output Characteristics, Feedback Accuracy Voltage
Parameter; Error Amplifier, Transconductance Parameter; and
Linear Regulator, VCCO Load Regulation and VIN to VCCO
Dropout Voltage Parameters, Table 1 ............................................. 3
Changes to Pin 4, Pin 16, and Pin 25 Descriptions, Table 3 ........ 8
Changes to Figure 5 and Figure 6 ................................................. 10
9/09—Revision 0: Initial Version
ADP1877SPECIFICATIONS All limits at temperature extremes are guaranteed via correlation using standard statistical quality control. VIN = 12 V. The specifications
are valid for TJ = −40°C to +125°C, unless otherwise specified. Typical values are at TA = 25°C.
Table 1.
ADP1877 Guaranteed by design. 2 Connect VIN to VCCO when VIN < 5.5 V. For applications with VIN < 5.5 V and VIN not connected to VCCO, keep in mind that VCCO = VIN − VDROPOUT. VCCO must be ≥
2.75 V for proper operation.
