L6712QTR STMicroelectronics, L6712QTR Datasheet - Page 8

• Manufacturer Part Number: L6712QTR
• Description: IC CTRLR DC/DC 2PH SYNC 36VFQFPN
• Manufacturer: STMicroelectronics
• Type: Step-Down (Buck)r

Specifications of L6712QTR

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 2
• Voltage - Output: 0.9 ~ 3.3 V
• Current - Output: 2A
• Frequency - Switching: 150kHz
• Voltage - Input: 12V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 36-VFQFN, 36-VFQFPN
• Power - Output: 3.5W
• Operating Temperature Range: - 40 C to + 125 C
• Mounting Style: SMD/SMT
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 497-4219-2

L6712A L6712
3
The device is an integrated circuit realized in BCD technology. It provides complete control logic and pro-
tections for a high performance dual-phase step-down converter optimized for high current DC/DC appli-
cations. It is designed to drive N-Channel Mosfets in a two-phase synchronous-rectified buck topology. A
180 deg phase shift is provided between the two phases allowing reduction in the input capacitor current
ripple, reducing also the size and the losses. The output voltage of the converter can be precisely regu-
lated, programming the VID pins, from 0.900 to 3.300V with a maximum tolerance of ±0.9% over temper-
ature and line voltage variations. The programmable Remote Sense Amplifier avoids the use of external
resistor divider allowing recovering drops across distribution lines and also adjusting output voltage to dif-
ferent values from the available reference. The device provides an average current-mode control with fast
transient response. It includes a 150kHz free-running oscillator externally adjustable through a resistor.
The error amplifier features a 15V/µs slew rate that permits high converter bandwidth for fast transient per-
formances. Current information is read across the lower mosfets R
in series to the LS mos in fully differential mode. The current information corrects the PWM outputs in order
to equalize the average current carried by each phase. Current sharing between the two phases is then
limited at ±10% over static and dynamic conditions unless considering the sensing element spread. Droop
effect can be programmed in order to minimize output filter and load transient response: the function can
be disabled and the current information available on the pin can be used for other purposes. The device
protects against Over-Current, with an OC threshold for each phase, entering in constant current mode.
Since the current is read across the low side mosfets, the device keeps constant the bottom of the induc-
tors current triangular waveform. When an Under Voltage is detected the device resets with all mosfets
OFF and suddenly re-starts. The device also performs a crowbar Over-Voltage protection that immediate-
ly latches the operations turning ON the lower driver and driving high the FAULT pin.
3.1 OSCILLATOR
The switching frequency is internally fixed at 150kHz. Each phase works at the frequency fixed by the os-
cillator so that the resulting switching frequency at the load side results in being doubled.
The internal oscillator generates the triangular waveform for the PWM charging and discharging with a
constant current an internal capacitor. The current delivered to the oscillator is typically 25µA
(Fsw=150kHz) and may be varied using an external resistor (R
SGND or Vcc. Since the OSC pin is maintained at fixed voltage (Typ. 1.237V), the frequency is varied
proportionally to the current sunk (forced) from (into) the pin considering the internal gain of 6KHz/µA.
In particular connecting it to SGND the frequency is increased (current is sunk from the pin), while con-
necting R
ing relationships:
Forcing 25µA into this pin, the device stops switching because no current is delivered to the oscillator
8/29
Device Description
R
R
OSC
OSC
OSC
to Vcc=12V the frequency is reduced (current is forced into the pin), according to the follow-
vs. 12V:
vs. GND:
F
SW
F
SW
=
=
150 KHz
150 KHz
[
[
] 12 1.237
–
]
------------------------ -
+
R
--------------- 6
R
–
1.237
OSC
OSC
⋅
⋅
6
kHz
---------- -
µA
kHz
---------- -
µA
=
=
150 kHz
OSC
150 kHz
dsON
[
) connected between OSC pin and
[
or across a sense resistor placed
]
]
+
–
----------------------------- - kHz
R
7.422 10
----------------------------- - kHz
R
6.457 10
OSC
OSC
[
⋅
[
KΩ
⋅
KΩ
6
]
7
]
[
[
]
]