PM6685 STMicroelectronics, PM6685 Datasheet - Page 24

• Manufacturer Part Number: PM6685
• Description: IC CTLR DUAL SYNC STDN 5X5VFQFPN
• Manufacturer: STMicroelectronics

Specifications of PM6685

• Applications: Controller, Notebook Power System
• Voltage - Input: 6 ~ 28 V
• Number Of Outputs: 2
• Voltage - Output: -3.3V, 5V
• Operating Temperature: 0°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 32-VFQFN, 32-VFQFPN
• Output Voltage: 5 V, 3.3 V
• Output Current: 0.1 A
• Input Voltage: 5.5 V to 28 V
• Mounting Style: SMD/SMT
• Maximum Operating Temperature: + 125 C
• Minimum Operating Temperature: - 10 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Device description
7.4
24/52
Figure 30. Circuitry for output ripple compensation
The integrator amplifier generates a current, proportional to the DC errors, which decreases
the output voltage in order to compensate the total static error, including the voltage drop on
PCB traces. In addition, C
voltage on COMP5/COMP3 pin is the sum of the reference voltage V
(see
and the output increases.
For example, we consider V
C
an AC path for the output voltage ripple. Then the COMP pin ripple is a replica of the output
ripple, with a DC value of Vr+25mV=925mV.
For more details about the output ripple compensation network, see the paragraph “ Closing
the integrator loop ” in the Design guidelines .
Pulse skip mode
If the SKIP pin is tied to ground, the device works in skip mode.
At light loads a zero-crossing comparator truncates the low-side switch on-time when the
inductor current becomes negative. In this condition the section works in discontinuous
conduction mode. The threshold between continuous and discontinuous conduction mode
is:
Equation 4
INT
>>C
Vr
Vr
Figure 30
COMP PIN
COMP PIN
VOLTAGE
VOLTAGE
OUTPUT VOLTAGE
OUTPUT VOLTAGE
FILT
, the C
). In fact when the voltage on the COMP pin reaches V
t
t
t
t
INT
D
D
D
D
∆V
∆V
∆V
∆V
DC voltage drop V
INT
L
L
L
L
OUT
provides an AC path for the output ripple. In steady state, the
ILOAD
=5V with an output ripple of ∆ V=50mV. Considering
CFILT
CFILT
CFILT
CFILT
CINT
CINT
RINT
RINT
CINT
CINT
RINT
RINT
(
SKIP
ROUT
ROUT
ROUT
ROUT
CINT
COMP
COMP
COMP
COMP
COUT
COUT
COUT
COUT
)
OUT
OUT
OUT
OUT
=
VCINT
VCINT
VCINT
VCINT
is about 5V-Vr+25mV=4.125V. C
V
IN
2
−
×
V
L
OUT
I=gm(V1-Vr)
I=gm(V1-Vr)
×
T
ON
RFb2
RFb2
RFb2
RFb2
Vr
Vr
Vr
Vr
gm
gm
gm
gm
V1
V1
V1
V1
+
+
RFb1
RFb1
RFb1
RFb1
Vr
Vr
Vr
Vr
r
r
, a fixed Ton begins
and the output ripple
+
+
-
-
Comparator
Comparator
Comparator
Comparator
PWM
PWM
PWM
PWM
INT
ensures
PM6685