cs51412g ON Semiconductor, cs51412g Datasheet - Page 12

• Manufacturer Part Number: cs51412g
• Description: 1.5a, 260 Khz And 520 Khz, Low Voltage Buck Regulators With External Bias Or Synchronization Capability
• Manufacturer: ON Semiconductor

where:
and conduction current contribute to the power loss of a
non-ideal switch. The power loss can be quantified as
where:
both high current and voltage during each switch transition.
This regulator has a 30 ns turn-off time and associated
power loss is equal to
not considered here.
ambient temperature, IC power dissipation and thermal
resistance of the package. The equation is shown as follows,
125°C to guarantee proper operation and avoid any damages
to the IC.
Using the BIAS Pin
notable at low load and high input voltage as will be
explained below.
when the BIAS pin is used. The circuitry shown is not the
actual implementation, but is useful in the explanation.
The power dissipated by the IC due to this current is
I
When the power switch turns on, the saturation voltage
V
The switching loss occurs when the switch experiences
The turn-on time is much shorter and thus turn-on loss is
The total power dissipated by the IC is sum of all the above
The IC junction temperature can be calculated from the
The maximum IC junction temperature shall not exceed
The efficiency savings in using the BIAS pin is most
Figure 17 will help to understand the increase in efficiency
BIAS
S
SAT
W IC + W Q ) W DRV ) W BASE ) W SAT ) W S
V
= DC switching current.
in
= saturation voltage of the power switch which is
shown in Figure 12.
W S +
W SAT +
T J + W IC
W BASE +
I S
Figure 17.
V IN
2
V O
V IN
V O 2
V IN
R qJA ) T A
I S
30 ns
CS51411, CS51412, CS51413, CS51414
P1
P2
V SAT
60
I S
f S
Internal
BIAS
http://onsemi.com
12
BIAS pin. When the BIAS pin is low, the logic turns P2 on
and current is routed to the internal bias circuitry from the
V
turns P1 on and current is routed to the internal bias circuitry
from the BIAS pin.
The input voltage range for V
voltage range for BIAS is 3.3 V to 6 V. The quiescent current
specification is 3 mA (min), 4 mA (typ), and 6.25 mA (max).
quiescent current number of 4 mA, the power would be:
regulator at 5 V instead of the output voltage. The BIAS pin
would normally be connected to the output voltage, but
adding an added switching regulator efficiency number here
would cloud this example. Now the internal BIAS circuitry
is being powered via 5 V. The resulting on chip power being
dissipated is:
maximum battery input voltage of 40 V, the maximum
quiescent current of 6.25 mA, and the lowest allowed BIAS
voltage for proper operation of 3.3 V;
Minimum Load Requirement
required for this regulator due to the predriver current
feeding the output. Placing a resistor equal to V
12 mA should prevent any voltage overshoot at light load
conditions. Alternatively, the feedback resistors can be
valued properly to consume 12 mA current.
Input Capacitor
current with an amplitude equal to the load current. This
pulsed current and the ESR of the input capacitors determine
the V
ripple, low ESR is a critical requirement for the input
capacitor selection. The pulsed input current possesses a
significant AC component, which is absorbed by the input
capacitors.
in
Internal bias to the IC can be supplied via the V
Here is an example of the power savings:
Using a typical battery voltage of 14 V and the typical
We'll assume the BIAS pin is connected to an external
The power savings is 35 mW.
Now, to demonstrate more notable savings using the
Powered from V
Powered from the BIAS pin:
The power savings is 229 mW.
As pointed out in the previous section, a minimum load is
In a buck converter, the input capacitor witnesses pulsed
pin. Conversely, when the BIAS pin is high, the logic
IN
ripple voltage, which is shown in Figure 18. For V
P + V
P + V
COMPONENT SELECTION
P + 40
P + 3.3
in
:
I + 14
I + 5
6.25e-3 + 250 mW
6.25e-3 + 21 mW
in
4e-3 + 21 mW
4e-3 + 56 mW
is 4.5 V to 40 V. The input
O
in
divided by
pin or the
IN