LM51031D HTC [HTC Korea TAEJIN Technology Co.], LM51031D Datasheet - Page 5

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

the PFET off. As V
oscillator capacitor (C
Timing capacitor(CS) charges via internal current
sources. C
IC and CS gets charged by the IT source
combination described by:
The internal Holdoff Comparator ensures that the
external PFET is off until V
GATE flip-flop (F2) from being set. This allows the
oscillator to reach its operating frequency before
enabling the drive output. Soft start is obtained by
clamping the V
to approximately 1/2 of the voltage at the CS pin
during startup, permitting the control loop and the
output voltage to slowly increase. Once the CS pin
charges above the Holdoff Comparator trip point of
0.7V, the low feedback to the V
the GATE flip-flop during COSC ’s charge cycle.
Once the GATE flip-flop is set, V
turns on the PFET. When V
charge sense comparator (A4) sets the V
comparator reference to 1.25V completing the startup
Fast PFET Buck Controller
cycle.
OSC
FB
gets charged by the current source
Figure 3. Voltage on Start Capacitor (V
comparator’s (A6) reference input
CC
Feedback Loop (V
and V
OSC
) and Soft start/Fault
CS
CS
C
> 0.7V, preventing the
continue to rise, the
exceeds 2.4V, the CS
FB
GATE
Comparator sets
goes low and
FB
FB
), During Startup, Normal and Fault Conditions
− 5 −
since there is no current sense resistor reguired.
capacitor voltage) reaches 2.5V during startup, the
LM51031 goes into a fast discharge mode. The fault
voltage is still below 1.15V when the CS pin reaches
2.4V, a valid fault condition has been detected. The
slow discharge comparator output goes high and
flop. The Vgate flip flop resets and the output switch is
turned off. The fault timing capacitor is slowly
discharged to 1.5V. The LM51031 then enters a normal
startup routine. If the fault is still present when the
slow discharge cycles repeat as shown in figure 2.
chance of erroneously detecting a load transient as a
Lossless Short Circuit Protection
The LM51031 has “lossless” short circuit protection
When the voltage at the CS pin (the fault timing
fault timing circuitry is enabled. During normal operation
the CS voltage is 2.6V. During a short circuit or a
transient condition, the output voltage moves lower and
the voltage at V
the output of the fault comparator goes high and the
timing capacitor, CS, discharges to 2.4V. If the V
enables gate G5 which sets the slow discharge flip
fault timing capacitor voltage reaches 2.5V, the fast and
If the V
2.4V a fault condition is not detected, normal operation
resumes and CS charges back to 2.6V. This reduces the
fault condition.
GS
), the Gate (V
FB
voltage is above 1.15V when CS reaches
FB
drops. If V
GATE
), and in the
FB
drops below 1.15V,
LM51031
FB
HTC