CS5212GD14 ONSEMI [ON Semiconductor], CS5212GD14 Datasheet - Page 10

• Manufacturer Part Number: CS5212GD14
• Description: Low Voltage Synchronous Buck Controller
• Manufacturer: ONSEMI [ON Semiconductor]

copper clad circuit boards will have approximate thermal
resistances (q
be performed to insure the design will dissipate the required
power under worst case operating conditions. Variables
considered during testing should include maximum ambient
temperature, minimum airflow, maximum input voltage,
maximum loading, and component variations (i.e. worst case
MOSFET R
the MOSFET’s heatsinks and will add heat and raise the
temperature of the circuit board and MOSFET. For any new
design, its advisable to have as much heatsink area as possible
– all too often new designs are found to be too hot and require
re−design to add heatsinking.
Compensation Capacitor Selection
30 mA. This current charging the capacitor on the COMP pin
is used as soft−start for the converter. The COMP pin is
going to ramp up to a voltage level that is within 70 mV of
what V
voltage that will determine the soft−start. Therefore, the
COMP capacitor can be established by the following
relationship:
where:
and will affect the ramp−up time. The value of the capacitor
on the COMP pin will have an effect on the loop response
and the transient response of the converter. Transient
response can be enhanced by the addition of a parallel
combination of a resistor and capacitor between the COMP
pin and the comp capacitor.
q
T
T
For TO−220 and TO−263 packages, standard FR−4
As with any power design, proper laboratory testing should
The nominal output current capability of the error amp is
soft−start = output ramp−up time
V
30 mA = COMP output current, typ.
The COMP output current range is given in the data sheet
SA
A
J
FFB(REG)
heatsink assuming direct mounting of the MOSFET (no
thermal “pad” is used).
temperature.
is the worst case ambient operating temperature.
is the specified maximum allowed junction
is the sink−to−ambient thermal impedance of the
FFB
DS(on)
is going to be when in regulation. This is the
SA
= V
) as shown below:
(in
Pad Size
0.75/484
2.0/1290
2.5/1612
C + 30 mA
0.5/323
1.0/645
1.5/968
FFB
). Also, the inductors and capacitors share
2
/mm
voltage when in regulation
2
)
V FFB(REG)
Single−Sided
1 oz. Copper
soft start
60−65°C/W
55−60°C/W
50−55°C/W
45−50°C/W
38−42°C/W
33−37°C/W
http://onsemi.com
10
R
resistor connected between the R
The grounded side of this resistor should be directly
connected to the SGND pin, without any other currents
flowing between the bottom of the resistor and the pin. Also,
avoid running any noisy signals under the resistor, since
injected noise could cause frequency jitter. The graph in
Figure 6 shows the required resistance to program the
frequency. Below 500 kHz, the following formula is
accurate:
where f
Differential Remote Sense Operation
provided by the CS5212. The positive remote sense is
implemented by bringing the output remote sense
connection to the positive load connection. A low value
resistor is connected from Vout to the feedback point at the
regulator to provide feedback in the instance when the
remote sense point is not connected.
connecting the SGND of the CS5212 to the negative of the
load return. Again, a low value resistor should be connected
between SGND and LGND at the regulator to provide
feedback in the instance when the remote sense point is not
connected. The maximum voltage differential between the
three grounds for this part is 200 mV.
Feedback Divider Selection
regulation will be 1.0 V. This voltage is compared to an
internal 1.0 V reference and is used to regulate the output
voltage. The bias current into the error amplifier is 1.0 mA
max, so select the resistor values so that this current does not
add an excessive offset voltage.
OSC
The switching frequency is programmed by selecting the
The ability to implement fully differential remote sense is
The negative remote sense connection is provided by
The feedback voltage measured at V
140
120
100
80
60
40
20
0
Selection
0
SW
is the switching frequency in kHz.
100
Figure 6. Frequency vs. R
R + 17544 f SW * 4 kW
200
300
Frequency (kHz)
400
OSC
500
pin and SGND (pin 7).
FB
OSC
600
during normal
700
800