PM6670ASTR STMicroelectronics, PM6670ASTR Datasheet - Page 34

• Manufacturer Part Number: PM6670ASTR
• Description: IC CTLR DDR2/3 MEM PS 24VFQFPN
• Manufacturer: STMicroelectronics

Specifications of PM6670ASTR

• Applications: Memory, DDR2/DDR3 Regulator
• Current - Supply: 800µA
• Voltage - Supply: 4.5 V ~ 36 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 24-VFQFN, 24-VFQFPN
• For Use With: 497-8412 - BOARD EVAL PM6670AS DDR2/3497-8411 - BOARD EVAL PM6670S DDR2/3
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 497-6305-2; PM6670ATR

Device description
7.1.9
7.1.10
34/53
Figure 38. Fast discharge and soft discharge options
Gate drivers
The integrated high-current gate drivers allow using different power MOSFETs. The high-
side driver uses a bootstrap circuit which is supplied by the +5 V rail. The BOOT and
PHASE pins work respectively as supply and return path for the high-side driver, while the
low-side driver is directly fed through VCC and PGND pins.
An important feature of the PM6670AS gate drivers is the adaptive anti-cross-conduction
circuitry, which prevents high-side and low-side MOSFETs from being turned on at the same
time. When the high-side MOSFET is turned off, the voltage at the PHASE node begins to
fall. The low-side MOSFET is turned on only when the voltage at the PHASE node reaches
an internal threshold (2.5 V typ.). Similarly, when the low-side MOSFET is turned off, the
high-side one remains off until the LGATE pin voltage is above 1 V.
The power dissipation of the drivers is a function of the total gate charge of the external
power MOSFETs and the switching frequency, as shown in the following equation:
Equation 23
The low-side driver has been designed to have a low-resistance pull-down transistor
(0.6 Ω typ.) in order to prevent undesired ignition of the low-side MOSFET due to the Miller
effect.
Reference voltage and bandgap
The 1.237 V internal bandgap reference has a granted accuracy of ±1% over the
0 °C to 85 °C temperature range. The VREF pin is a buffered replica of the bandgap voltage.
It can supply up to ±100 μA and is suitable to set the intermediate level of MODE, DDRSEL
and DSCG multifunction pins. A 100 nF (min.) bypass capacitor toward SGND is required to
enhance noise rejection. If VREF falls below 0.87 V (typ.), the system detects a fault
condition and all the circuitry is turned OFF.
An internal divider derives a 0.9 V±1% voltage (Vr) from the bandgap. This voltage is used
as a reference by the switching regulator output. The over-voltage protection, the under-
voltage protection and the Power-Good signal are also referred to Vr.
400mV
400mV
VTT
VTT
VDDQ
VDDQ
Fast discharge
Fast discharge
Doc ID 14436 Rev 2
P
Soft discharge
Soft discharge
D
(
driver
)
=
V
DRV
⋅
Q
VTT
VTT
VDDQ
VDDQ
g
⋅
f
SW
Soft discharge
Soft discharge
PM6670AS