l6712a STMicroelectronics, l6712a Datasheet - Page 15

• Manufacturer Part Number: l6712a
• Description: Two-phase Interleaved Dc/dc Controller
• Manufacturer: STMicroelectronics

in the regulated output voltage, the "native" offset of the amplifier must be multiplied by the term
K
the offset.
If remote sense is not required, it is enough connecting R
comes not connected and still senses the output voltage through the remote amplifier. In this case the use
of the external resistors R1 and R2 becomes optional and the Remote Sense Amplifier can simply be con-
nected as a "buffer" to keep VSEN at the regulated voltage (See figure 7). Avoiding use of Remote Am-
plifier saves its offset in the accuracy calculation but doesn't allow remote sensing.
INTEGRATED DROOP FUNCTION (Optional)
Droop function realizes dependence between the regulated voltage and the delivered current (Load Reg-
ulation). In this way, a part of the drop due to the output capacitor ESR in the load transient is recovered.
As shown in Figure 8, the ESR drop is present in any case, but using the droop function the total deviation
of the output voltage is minimized.
Connecting DROOP pin and FB pin together, forces a current I
into the feedback resistor R
Amplifier gain, the Output Characteristic is then given by the following relationship (when droop enabled):
with a remote amplifier gain of 1/2, the regulated output voltage results in being doubled.
The Droop current is equal to 50 µ A at nominal full load and 70 µ A at the OC intervention threshold, so the
maximum output voltage deviation is equal to:
Droop function is provided only for positive load; if negative load is applied, and then I
is sunk from the FB pin. The device regulates at the voltage programmed by the VID.
If this effect is not desired, shorting DROOP pin to SGND, the device regulates as a Voltage Mode Buck
converter.
Figure 8. Load Transient response (Left) and DROOP pin connection (Right).
MONITOR AND PROTECTIONS
The device monitors through pin VSEN the regulated voltage in order to build the PGOOD signal and man-
age the OVP / UVP conditions.
I
V
V
V
OS
∆V
PGOOD. Power good output is forced low if the voltage sensed by VSEN is not within ±12% (Typ.) of
the programmed value (RA_Gain=1). It is an open drain output and it is enabled only after the soft start
MAX
NOM
MIN
= [1+(1/RA_Gain)] because a voltage generator insisting on the non-inverting input represents
FUL L PO S ITIVE
DROOP PIN = FB PIN
V
DROOP PIN = GND
–
OUT
=
------------------------ -
RA_Gain
ESR DROP
–
LO AD
1
=
–
FB
⋅
------------------------ - R
RA_Gain
(
VID R
implementing the load regulation dependence. If RA_Gain is the Remote
1
–
⋅
FB
F B
⋅
I
⋅
DROOP
50µA
)
=
R2
------------------------ -
RA_Gain
Remote
V
OUT
R1
FB
∆V
1
FBR
directly to the regulated voltage: VSEN be-
O C INTE RVENTIO N
DROOP
FBG
R1
Remote
Ground
–
⋅
§
©
VID R
R2
, proportional to the output current,
AMPLIFIER
REMOTE
–
Short to GND if DROOP function is not
implemented (Classic Voltage Mode).
VSEN
FB
R
FB
⋅
=
R
--------------------- - I
–
DROOP
SENSE
------------------------ - R
RA_Gain
Rg
I
DROOP
Reference
INFOx
1
L6712A L6712
FB
⋅
C
OUT
<0, no current
F
⋅
AMPLIFIER
FB
ERROR
R
·
¹
F
⋅
70µA
COMP
15/27