cs5157h ON Semiconductor, cs5157h Datasheet - Page 10

• Manufacturer Part Number: cs5157h
• Description: Cpu 5-bit Synchronous Buck Controller
• Manufacturer: ON Semiconductor

Short Circuit Protection
provided, requiring only the Soft−Start capacitor to
implement. If a short circuit condition occurs (V
the V
the MOSFET to shut off, disconnecting the regulator from it’s
input voltage. The Soft−Start capacitor is then slowly
discharged by a 2.0 mA current source until it reaches it’s
lower 0.7 V threshold. The regulator will then attempt to
restart normally, operating in it’s extended off time mode with
a 50% duty cycle, while the Soft−Start capacitor is charged
with a 60 mA charge current.
will not achieve the 1.0 V low V
before the Soft−Start capacitor is charged to it’s upper 2.5 V
threshold. If this happens the cycle will repeat itself until the
short is removed. The Soft−Start charge/discharge current
ratio sets the duty cycle for the pulses (2.0 mA/60 mA = 3.3%),
while actual duty cycle is half that due to the extended off time
mode (1.65%).
regulator components, input power supply, and PC board
traces than occurs with constant current limit protection (see
Figures 12 and 13).
will rise above the 1.0 V level, preventing the FAULT latch
from being set, allowing normal operation to resume.
Delivered While the Soft−Start Capacitor Charges, and
A lossless hiccup mode short circuit protection feature is
If the short circuit condition persists, the regulator output
This protection feature results in less stress to the
If the short circuit condition is removed, output voltage
Figure 12. CS5157H Demonstration Board Hiccup
Trace 4− 5.0 V Supply Voltage (2.0 V/div.)
Trace 3− Soft−Start Timing Capacitor (1.0 V/div.)
Trace 2− Inductor Switching Node (2.0 V/div.)
Mode Short Circuit Protection. Gate Pulses are
FFB
low comparator sets the FAULT latch. This causes
Cease During Discharge
M 25.0 ms
FFB
comparator threshold
FFB
< 1.0 V),
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CS5157H
10
Overvoltage Protection
normal operation of the V
additional external components. The control loop responds
to an overvoltage condition within 100 ns, causing the top
MOSFET to shut off, disconnecting the regulator from it’s
input voltage. The bottom MOSFET is then activated,
resulting in a “crowbar” action to clamp the output voltage
and prevent damage to the load (see Figures 14 and 15 ). The
regulator will remain in this state until the overvoltage
condition ceases or the input voltage is pulled low. The
bottom FET and board trace must be properly designed to
implement the OVP function.
Overvoltage protection (OVP) is provided as result of the
Trace 4− 5.0 V from PC Power Supply (2.0 V/div.)
Trace 2− Inductor Switching Node (2.0 V/div.)
Figure 13. Startup with Regulator Output Shorted
Trace 4− 5.0 V from PC Power Supply (5.0 V/div.)
Trace 1− Regulator Output Voltage (1.0 V/div.)
Trace 2− Inductor Switching Node (5.0 V/div.)
Cycle, Crow−Barring the Input Voltage to Ground
Figure 14. OVP Response to an Input−to−Output
Short Circuit by Immediately Providing 0% Duty
M 10.0 ms
M 50.0 ms
2
control topology and requires no