LTC1873_15 Datasheet, PDF (1/32 Pages) Linear Technology – Dual 550kHz Synchronous 2-Phase Switching Regulator Controller with 5-Bit VID

LTC1873
Dual 550kHz Synchronous
2-Phase Switching Regulator
Controller with 5-Bit VID
FEATURES
s _{Two Independent PWM Controllers in One Package}
s _{Side 1 Output Is Compliant with Intel Desktop}
VRM 8.4 Specifications (Includes 5-Bit VID DAC)
s _{1.3V to 3.5V Output Voltage with 50mV/100mV Steps}
s _{Two Sides Run Out-of-Phase to Minimize CIN}
s _{All N-Channel External MOSFET Architecture}
s _{No External Current Sense Resistors Required}
s _{Precison Internal 0.8V ±1% Reference}
s _{550kHz Switching Frequency Minimizes External}
Component Size
s _{Very Fast Transient Response}
s _{Up to 25A Output Current per Channel}
s _{Low Shutdown Current: < 100µA}
s _{Small 28-Pin SSOP Package}
U
APPLICATIO S
s _{Microprocessor Core and I/O Supplies}
s _{Multiple Logic Supply Generator}
s _{High Efficiency Power Conversion}
s _{Chipset Power Supply}
DESCRIPTIO
The LTC^®1873 is a dual switching regulator controller opti-
mized for high efficiency with low input voltages. It includes
two complete, on-chip, independent switching regulator con-
trollers. Each is designed to drive a pair of external
N-channel MOSFETs in a voltage mode feedback, synchro-
nous buck configuration. The LTC1873 includes digital out-
put voltage adjustment on side 1 that conforms to the Intel
Desktop VID specification. A constant-frequency, true PWM
design minimizes external component size and cost and
optimizes load transient performance. The synchronous buck
architecture automatically shifts to discontinuous and then to
Burst Mode^TM operation as the output load decreases, ensur-
ing maximum efficiency over a wide range of load currents.
The LTC1873 features an onboard reference trimmed to 1%
and delivers better than 1.5% regulation at the converter
outputs over all combinations of line, load and temperature.
Each channel can be enabled independently; with both chan-
nels disabled, the LTC1873 shuts down and supply current
drops below 100µA.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a trademark of Linear Technology Corporation.
TYPICAL APPLICATIO
Low Cost Desktop CPU Supply with RDRAM Keepalive
4.5V TO 5.5V
STBY/ON
10k
0.1%
1k
1k
4.75k ⁺
0.1%
330pF
68k
QSS1
QSS2
+
10Ω
C_IN
10µF
V_CC
PV_CC
FB2
56pF
COMP2
BOOST2
TG2
SW2
RUN/SS2
RUN/SS1
0.1µF
BG2
47k
I_MAX2
LTC1873 ^FAULT
SENSE
BOOST1
220pF
56k
5-BIT VID
FB1
39pF
COMP1
FCB
VID4:0
SGND
TG1
SW1
BG1
33k
I_MAX1
PGND
MBR0530T
IN OUT
1µF LT1761
GND ADJ
QT2
1µF
L2
QB2
MBR0530T
QT1B
QT1A
1µF
L1
QB1B
QB1A
16.2k
0.1%
16.9k
0.1%
+
V_RDRAM
2.5V/7A
2.45V/100mA STANDBY
C_OUT2
+
1873 TA01
V_CORE
1.3V TO 3.5V
20A
C_OUT1
C_IN = SANYO 10MV1200GX (6 IN PARALLEL)
C_OUT1 = SANYO 6MV1500GX (8 IN PARALLEL)
C_OUT2 = SANYO 6MV1500GX (3 IN PARALLEL)
L1: 1µH SUMIDA CEP125-1R0MC-H
L2: 2.2µH COILTRONICS UP2B-2R2
QSS1, QSS2: MOTOROLA MMBT3904LT1
QT1A, QT1B, QB1A, QB1B: FAIRCHILD FDS6670A
QT2, QB2: 1/2 SILICONIX Si4966
1