Sharp IQ-9B01 Bedienungsanleitung PDF herunterladen (Seite 5)

IXD9213/14

Doc. No. IXD9213_DS, Rev. N0

Characteristics subject to change without notice

The Current Feedback circuit monitors current of the P-channel transistor at each switching cycle, and modulates

output signal from the Error Amplifier to provide additional feedback. This guarantees a stable converter operation

even with low ESR ceramic load capacitor.

Reference Voltage Source

The Reference Voltage Source provides the reference voltage to ensure stable output voltage of the DC/DC

converter. After CE pin activates IC, reference voltage connected to the error amp increases linearly during the

soft-start interval. This allows the output voltage rise in proportion to the reference voltage. This operation prevents

inrush current and allows the output voltage rise smoothly.

If the output voltage does not reach nominal output voltage within the soft start time due heavy load, or a large

output capacitor, the current restriction function activates and prevents an excessive increase of the input current,

allowing the output voltage to rise smoothly.

Minimum On-time Generator

The Minimum On-time Generator produces signal needed for PWM operation, and signals to synchronize all the

internal circuits. The on time is set as function of the input and output voltages as t

= V

OUT

x 333 (ns).

Error Amplifier

The Error Amplifier monitors output voltage through resistive divider connected to V

OUT

pin. If output voltage falls

below preset value and Error Amplifier’s input signal becomes less than internal reference voltage, the Error

Amplifier/s output signal increases. That results in wider PWM pulse for switching transistor to increase output

voltage. The gain and frequency characteristics of the error amplifier output are fixed internally to optimize IC

performance.

Switching Frequency

The switching frequency is a function of the on time (t

), which is determined by the input voltage and output

voltage, as given by the equation below.

OSC

(MHz) = V

OUT

/ (V

×t

(ns))

100% Duty Cycle Mode

When the load current is heavy and the voltage difference between input and output voltage is small, 100% duty

cycle mode activates and it keeps the P-channel MOSFET in on-state. 100% duty cycle mode attains high output

voltage stability and high-speed response under all load conditions, from light to heavy, even in conditions where

the dropout voltage is low.

Current Limiter

The Current Limiter circuit monitors current flowing through the P-channel transistor connected to the Lx pin. When

transistor’s current is greater than a specified level, the Current Limiter turns off P-channel transistor immediately.

After that, the Current Limiter turns off too, returning to monitoring mode.

The driver transistor turns on at the next cycle, but the Current Limiter will turn it off immediately, if an over- current

exists. When the over current state is eliminated, the IC resumes its normal operation.

PWM/PFM Selection Circuit

PWM is a continuous conduction mode operation, and utilizes a stable switching frequency determined by on-time

generator.

PWM/PFM auto switching mode allows utilize a discontinuous conduction mode at light loads, decreasing the

switching frequency to reduce switching losses and improve efficiency, while returns to PWM mode and stable

frequency at high load.

The IXD9213 series operate in PWM mode only, while the IXD9214 series operate in PWM/PFM auto switching

mode.

UVLO Circuit

When the V

pin voltage becomes 2.0 V or lower, the P-channel transistor is forced OFF to prevent false pulse

output caused by unstable operation of the internal circuitry. When the V

pin voltage becomes 2.10 V or higher,

switching operations resume with the soft start. The soft start function operates even when the V

voltage falls

below the UVLO threshold for a very short time. The UVLO circuit does not cause a complete shutdown of the IC,

but causes pulse output to be suspended; therefore, the internal circuitry remains in operation.

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