PM6685 STMicroelectronics, PM6685 Datasheet - Page 22

• 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
22/48
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+25 mV =925 mV.
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
For higher loads the inductor current doesn’t cross the zero and the device works in the
same way as in PWM mode and the frequency is fixed to the nominal value.
INT
>>C
Figure
Vr
Vr
FILT
COMP PIN
COMP PIN
VOL TA GE
VOL TA GE
OU TPU T VOLTAGE
OU TPU T VOLTAGE
30). In fact when the voltage on the COMP pin reaches V
, the C
t
t
t
t
INT
D
D
D
D
? V
? V
DC voltage drop V
? V
? V
INT
L
L
L
L
OUT
provides an AC path for the output ripple. In steady state, the
ILOAD
Doc ID 11674 Rev 8
=5 V with an output ripple of ΔV=50m V. Considering
CF ILT
CF ILT
CF ILT
CF ILT
C INT
C INT
R INT
R INT
CINT
CINT
RINT
RINT
(
SKIP
CINT
R OU T
R OU T
ROUT
ROUT
COMP
COMP
COMP
COMP
COUT
COUT
COUT
COUT
)
=
OUT
OU T
OUT
OU T
VCINT
VC INT
VCINT
VC INT
is about 5 V-Vr+25 mV=4.125 V. 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
g m
gm
g m
gm
V1
V1
V1
V1
+
+
R Fb 1
R Fb 1
RF b1
RF b1
Vr
Vr
Vr
Vr
r
r
, a fixed Ton begins
and the output ripple
+
+
-
-
C om pa rator
C om pa rator
Co mp arator
Co mp arator
PWM
PWM
PWM
PWM
INT
ensures
PM6685