PM6641 STMicroelectronics, PM6641 Datasheet - Page 28

• Manufacturer Part Number: PM6641
• Description: IC MONO VR DDR2/3 PC VFQFPN-48
• Manufacturer: STMicroelectronics

Specifications of PM6641

• Applications: Converter, DDR2, DDR3
• Voltage - Input: 2.7 ~ 5.5 V
• Number Of Outputs: 3
• Voltage - Output: 0.8 ~ 5.5 V
• Operating Temperature: 0°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 48-VFQFN
• Output Voltage: 0.9 V
• Output Current: 3 A
• Input Voltage: 2.7 V to 5.5 V
• Switching Frequency: 1000 KHz
• Operating Temperature Range: - 40 C to + 125 C
• Mounting Style: SMD/SMT
• For Use With: 497-8425 - KIT EVAL PM6641 CHIPSET/DDR2/3
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Device description
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Outputs soft-start
The soft-start function of each switching regulator is achieved by ramping up the SS pin
voltage with a constant slew rate dV/dt.
When the switching section is enabled (EN high), the SS pin constant current charges the
capacitor connected between SS and ground pins.
The SS voltage is used as reference of the switching regulator and the output voltage of the
converter follows the ramp of the SS voltage. When the SS pin voltage is higher than 0.8 V,
the error amplifier uses the internal 0.8 V ±1% reference to regulate the output voltage.
Figure 31. SW regulator programmable soft-start
During the soft-start period the current limit is set to the nominal value.
The dV/dt slope is set by charging the external capacitor with a 10 µA current. The
capacitance values has to be of the order of magnitude of 10 nF for a 1 msec soft-start
duration, as pointed out by the following formula:
Equation 6
During the soft-start the output under voltage management is not enabled, whereas the
output over voltage, the current limit and the thermal overheat are always monitored.
When the first switching regulator is turned on the output soft-start begins after an additional
delay of about 180 µs, due to PM6641 initializing and fuses reading.
SS_1Sx
C
Doc ID 13510 Rev 3
=
I
Δ
Δ ⋅
Iss
V
SS DO
t
=
10
μ
0
A
8 .
⋅
V
1
ms
VREF
=
12
5 .
nF
Regulator
SW
PM6641