LM51031D HTC [HTC Korea TAEJIN Technology Co.], LM51031D Datasheet - Page 6

• Manufacturer Part Number: LM51031D
• Description: Fast PFET Buck Controller
• Manufacturer: HTC [HTC Korea TAEJIN Technology Co.]

A block diagram of a typical buck regulator is shown
in Figure 4. If we assume that the output transistor is
initially off, and the system is in discontinuous
operation, the inductor current IL is zero and the
output voltage is at its nominal value. The current
drawn by the load is supplied by the output
capacitor C
below the threshold established by the feedback
Specications 12 V to 5.0 V, 3.0 A Buck Controller
1) Duty Cycle Estimates
is limited to 80% min, it is necessary to estimate the
duty cycle for the various input condidtions over the
complete operating range.
Fast PFET Buck Controller
Buck Regulator Operation
The duty cycle for a buck regulator operating in a
Since the maximum duty cycle D, of the LM51031
Vin = 12 V ±20% (i.e. 14.4 V max, 121 V nom,
9.6 V min)
Vout = 5.0 V±2%
Iout = 0.3 A to 3.0 A
Output ripple voltage < 50 mV max
Efficiency > 80%
f
SW
LM51031 Design Example
= 200 kHz
O
. When the voltage across C
Figure 4. Buck Regulator Block Diagram
APPLICATIONS INFORMATION
O
drops
− 6 −
the power transistor Q1 switches on and current flows
through the inductor to the output. The inductor current
rises at a rate determined by (V
The duty cycle (or “on” time) for the LM51031 is limited
to 80%. If output voltage remains to 80%. If output voltag
change time, the Q1 does not turn on, skipping the pulse
resistors R1 and R2 and he reference voltage V
remains higher than nominal during the entire C
continuous conduction mode is given by:
where:
TJ 100°C.
becomes:
V
If VF = 0.60 V and VSAT = 0.60 V then the above equati
SAT
= R
DS
(ON) × I
OUT
max and R
IN
− V
DS
OUT
(
ON
LM51031
)/L.
) is the value at
OSC
HTC
REF
,