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NCP3064B

Inverting Converter, Switching Regulator - Buck Boost, ON/OFF Function 1.5 A

ON Semiconductor 

NCP3064, NCP3064B, NCV3064

Peak Current Sense Comparator

With a voltage ripple gated converter operating under

normal conditions, output switch conduction is initiated by

the Voltage Feedback comparator and terminated by the

oscillator. Abnormal operating conditions occur when the

converter output is overloaded or when feedback voltage

sensing is lost. Under these conditions, the Ipk Current

Sense comparator will protect the Darlington output Switch.

The switch current is converted to a voltage by inserting a

fractional W resistor, RSC, in series with VCC and the

Darlington output switch. The voltage drop across RSC is

monitored by the Current Sense comparator. If the voltage

drop exceeds 200 mV with respect to VCC, the comparator

will set the latch and terminate output switch conduction on

a cycle−by−cycle basis. This Comparator/Latch

configuration ensures that the Output Switch has only a

single on−time during a given oscillator cycle.

Real

Vturn−off on

Rs Resistor

Vipk(sense)

I1

di/dt slope

Io

t_delay

I through the

Darlington

Switch

Figure 14. Current Sense Waveform

The VIPK(Sense) Current Limit Sense Voltage threshold is

specified at static conditions. In dynamic operation the

sensed current turn−off value depends on comparator

response time and di/dt current slope.

Real Vturn−off on Rsc resistor

Vturn_off = Vipk(sense) + Rs*(tdelay*di/dt)

Typical Ipk comparator response time tdelay is 350 ns. The

di/dt current slope is growing with voltage difference on the

inductor pins and with decreasing inductor value. It is

recommended to check the real max peak current in the

application at worst conditions to be sure that the maximum

peak current will never get over the 1.5 A Darlington Switch

Current maximum rating.

Thermal Shutdown

Internal thermal shutdown circuitry is provided to protect

the IC in the event that the maximum junction temperature

is exceeded. When activated, typically at 160°C, the Output

Switch is disabled. The temperature sensing circuit is

designed with 10°C hysteresis. The Switch is enabled again

when the chip temperature decreases to at least 150°C

threshold. This feature is provided to prevent catastrophic

failures from accidental device overheating. It is not

intended to be used as a replacement for proper

heat−sinking.

Output Switch

The output switch is designed in a Darlington

configuration. This allows the application designer to

operate at all conditions at high switching speed and low

voltage drop. The Darlington Output Switch is designed to

switch a maximum of 40 V collector to emitter voltage and

current up to 1.5 A

ON/OFF Function

The ON/OFF function disables switching and puts the part

into a low power consumption mode. A PWM signal up to

1 kHz can be used to pulse the ON/OFF and control the

output. Pulling this pin below the threshold voltage (~1.4 V)

or leaving it open turns the regulator off and has a standby

current <100 mA. Pulling this pin above 1.4 V (up to 25 V

max) allows the regulator to run in normal operation. If the

ON/OFF feature is not needed, the ON/OFF pin can be

connected to the input voltage VCC, provided that this

voltage does not exceed 25 V.

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