Rainbow Electronics MAX1545 - Manual (Page 19)

MAX1519/MAX1545
Dual-Phase, Quick-PWM Controllers for
Programmable CPU Core Power Supplies
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where f SLEW = 500kHz ✕ 30k Ω/R
TIME , V DAC is the DAC
setting when the controller begins the shutdown
sequence, and V
LSB = 25mV is the DAC’s smallest volt-
age increment. Slowly discharging the output capacitors
by slewing the output over a long period of time
(4/f
SLEW ) keeps the average negative inductor current
low (damped response), thereby eliminating the nega-
tive output voltage excursion that occurs when the con-
troller discharges the output quickly by permanently
turning on the low-side MOSFET (underdamped
response).
This eliminates the need for the Schottky diode normally
connected between the output and ground to clamp the
negative output voltage excursion. When the DAC
reaches the 0V setting, DL_ goes high, DH_ goes low,
the reference turns off, and the supply current drops to
about 1µA. When a fault condition—output undervoltage
lockout, output overvoltage lockout (MAX1545), or ther-
mal shutdown—activates the shutdown sequence, the
controller sets the fault latch to prevent the controller from
restarting. To clear the fault latch and reactivate the con-
troller, toggle SHDN or cycle V
CC power below 1V.
MANUFACTURER PHONE WEBSITE
BI Technologies 714-447-2345 (USA) www.bitechnologies.com
Central Semiconductor 631-435-1110 (USA) www.centralsemi.com
Coilcraft 800-322-2645 (USA) www.coilcraft.com
Coiltronics 561-752-5000 (USA) www.coiltronics.com
Fairchild Semiconductor 888-522-5372 (USA) www.fairchildsemi.com
International Rectifier 310-322-3331 (USA) www.irf.com
Kemet 408-986-0424 (USA) www.kemet.com
Panasonic 847-468-5624 (USA) www.panasonic.com
Sanyo 65-6281-3226 (Singapore) www.secc.co.jp
Siliconix (Vishay) 203-268-6261 (USA) www.vishay.com
Sumida 408-982-9660 (USA) www.sumida.com
Taiyo Yuden
03-3667-3408 (Japan)
408-573-4150 (USA)
www.t-yuden.com
TDK
847-803-6100 (USA)
81-3-5201-7241 (Japan)
www.component.tdk.com
TOKO 858-675-8013 (USA) www.tokoam.com
Table 2. Component Suppliers
Figure 2. Power-Up and Shutdown Sequence Timing Diagram
VID (D0–D4)
V CORE
t VROK(START)
3ms, TYP
SOFT-SHUTDOWN
1LSB PER 4 R
TIME CYCLES
SOFT-START
1LSB PER R TIME CYCLE
VROK
DO NOT CARE
SHDN