Rainbow Electronics MAX1855 - Manual

General Description
The MAX1716/MAX1854/MAX1855 step-down con-
trollers are intended for core CPU DC-DC converters in
notebook computers. They feature a dynamically
adjustable output (5-bit DAC), ultra-fast transient
response, high DC accuracy, and high efficiency need-
ed for leading-edge CPU core power supplies. Maxim's
proprietary Quick-PWM™ quick-response, constant-on-
time PWM control scheme handles wide input/output
voltage ratios with ease and provides 100ns “instant-on”
response to load transients while maintaining a relative-
ly constant switching frequency.
The MAX1716/MAX1854/MAX1855 are designed
specifically for CPU core applications requiring a volt-
age-positioned supply. The voltage-positioning input
(VPS), combined with a high DC accuracy control loop,
is used to implement a power supply that modifies its
output set point in response to the load current. This
arrangement decreases full-load power dissipation and
reduces the required number of output capacitors.
The 28V input range of the MAX1716/MAX1854/MAX1855
enables single-stage buck conversion from high-volt-
age batteries for the maximum possible efficiency.
Alternatively, the devices’ high-frequency capability
combined with two-stage conversion (stepping down
the +5V system supply instead of the battery) allows
the smallest possible physical size. The output voltage
can be dynamically adjusted through the 5-bit digital-
to-analog converter (DAC) inputs.
The MAX1716/MAX1854/MAX1855 are available in a
24-pin QSOP package. For applications requiring
SpeedStep™ power control (see the MAX1717).
________________________Applications
Notebook Computers
Docking Stations
CPU Core Supply
Single-Stage (BATT to V CORE ) Converters
Two-Stage (+5V to V CORE ) Converters
Features
♦ High-Efficiency Voltage Positioning
♦ Quick-PWM Architecture
♦ ±1% V
OUT Line-Regulation Accuracy
♦ Adjustable Output Range (5-Bit DAC)
MAX1716: 0.925V to 1.6V
MAX1854: 0.925V to 2.0V
MAX1855: 0.600V to 1.75V
♦ 2V to 28V Input Range
♦ 200/300/400/550kHz Switching Frequency
♦ Output Undervoltage Protection
♦ Overvoltage Protection (MAX1716/MAX1855)
♦ Drive Large Synchronous-Rectifier MOSFETs
♦ 1.7ms Digital Soft-Start
♦ 700µA I
CC Supply Current
♦ 1µA Shutdown Supply Current
♦ 2V ±1% Reference Output
♦ V
GATE Transition-Complete Indicator
♦ Small 24-Pin QSOP Package
MAX1716/MAX1854/MAX1855
High-Speed, Adjustable, Synchronous Step-Down
Controllers with Integrated Voltage Positioning
________________________________________________________________ Maxim Integrated Products 1
19-1758; Rev 0; 8/00
For free samples and the latest literature, visit www.maxim-ic.com or phone 1-800-998-8800.
For small orders, phone 1-800-835-8769.
Pin Configuration appears at end of data sheet. Quick-PWM is a trademark of Maxim Integrated Products.
SpeedStep is a trademark of Intel Corp.
Ordering Information
PART TEMP. RANGE PIN-PACKAGE
MAX1716EEG -40 °C to +85°C 24 QSOP
MAX1854EEG -40 °C to +85°C 24 QSOP
MAX1855EEG -40 °C to +85°C 24 QSOP
Typical Operating Circuit
VGATE
DH
LX
DL
CS
VPS
BST
+5V INPUT
REF
ILIM
D0
D1
D2
D3
D4
SKIP
CC
GND
PGND
FB
MAX1716
MAX1854
MAX1855
TON
V+
V CC V
DD
SHDN
OUTPUT
DAC
INPUTS
BATTERY
2V TO 28V