Product Specification
IXD3235/36/37
Error Amplifier
The Error Amplifier monitors output voltage through resistive divider connected to VOUT (FB) 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 and respectively longer ON time for switching
transistor to increase output voltage. The gain and frequency characteristics of the error amplifier output are fixed
internally to optimize IC performance.
Current Limiter
The Current Limiter circuit monitors current flowing through the P-channel transistor connected to the Lx pin, and
combines function of the current limit and operation suspension.
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.
The IC waits for end of the over current state repeating above steps (t1 on figure below). If an over-current state
continues for a few ms with IC repeatedly performing above steps, the Current Limiter latches the P-channel
transistor in OFF state, and IC suspends operations (t2 on figure below). To restart IC operation after this condition,
either EN pin should be toggled H – L – H, or VIN pin voltage should be set below UVLO to resume operations from
soft start.
The suspension mode is not a standby mode. In the suspension mode, pulse output is suspended; however,
internal circuitries remain in operation mode consuming power.
Short-Circuit Protection
The short-circuit protection monitors the RFB1/RFB2 divider voltage (FB point in the block diagram). If output is
accidentally shorted to the ground, FB voltage starts falling. When this voltage becomes less than half of the
reference voltage (VREF) and P-channel switching transistor’s current is more than the ILIM threshold, the Short-
Circuit Protection turns off and latches quickly the P-channel transistor.
At D/E/F/G series, Short Circuit Protection starts once FB voltage becomes less than 0.25 of reference voltage
(VREF), disregard to transistor’s current.
To restart IC operation after this condition, either EN pin should be toggled H – L – H, or VIN pin voltage should be
set below UVLO to resume operations from soft start.
The sharp load transients creating a voltage drop at the VOUT, propagate to the FB point through CFB, that may
result in Short Circuit protection operating at voltages higher than 1/2 VREF voltage.
UVLO Circuit
When the VIN pin voltage becomes 1.4V or lower, the P-channel transistor is forced OFF to prevent false pulse
output caused by unstable operation of the internal circuitry. When the VIN pin voltage becomes 1.8 V or higher,
switching operations resume with the soft start. The soft start function operates even when the VIN voltage falls
PS034201-0515
PRELIMINARY
10
ZILOG [ ZILOG, INC. ]
