Daattaasshheeeett
BD99010EFV-M, BD99011EFV-M
(5) Error amplifier
The error amplifier compares the output feedback voltage to the 1.2V internal reference voltage and outputs the
difference as current to the COMP pin, which voltage is used to determine the switching duty cycle. A t initial
startup when the soft start works, the COMP voltage is limited to the soft start voltage. Moreover, the external
resistor and capacitor are required to COMP pin as phase compensation circuit.
(6) PWM modulator.
The PWM modulator converts the voltage at the COMP terminal to a continuous variable duty cycle that controls
the output power transistors. At very low input voltages the duty cycle can become 1 indicating the high-side
power transistor continuously in on-state. At very high input voltages the duty cycle becomes very small but
limited at an on-time of about 200ns. It should be noted that at high oscillation frequency settings this could lead
to random pulse skipping. For instance at 500 kHz the duty cycle is limited to values larger than 200ns / 2µs =
10%. This means that for 3.3V output the input voltage is limited to 33 V when avoiding random pulse skips. In
case, a higher input voltage is required the switching frequency has to be chosen lower.
(7) Oscillator
The oscillation frequency is determined by the current going through the external resistor RT at constant voltage
of ca. 0.3V. The frequency can be set in the range between 200kHz to 500kHz. It should be noted that the
frequency increases ca. 10% when the input voltage VIN is lower than 4.5 V because in that condition the
internal supply voltage VREG is also lowered.
(8) VREGB pin and Low input voltage detection (LVIN)
VREGB is the supply voltage of the high-side driver and output power transistor. VREGB voltage is referenced
from PVIN at voltage with 7.2V (typ.). When VIN voltage becomes below 6V (typ.), the LVIN circuit is activated
and VREGB is shorted to GND. By doing so the output power transistor is driven with the full supply voltage at
cold cranking conditions.
An external capacitor is required between PVIN and VREGB pin. A ceramic capacitor with 0.1μF or low ESR type
is recommended.
(9) Overcurrent protection (OCP)
The overcurrent protection is activated when the SW current exceeds 3.3A (typ.). Once activated the ON duty
cycle will be limited and the output voltage lowered.
(10) Short circuit protection (SCP) and SCP counter
The short circuit protection is activated after the output voltage (FB voltage) drops below 67% of the nominal
voltage level and the overcurrent protection is activated (except during startup). This indicated an output short
and the short circuit protection will be activated.
When the short circuit protection is activated, for a period of 1024 cycles of oscillation frequency, switching will
be terminated by turning off the output transistors and the SS and COMP pins discharged. After this time out
period the switching will resume including soft start.
(11) Under voltage lockout circuit (UVLO)
If the VIN drops below 3.4V (typ.) the UVLO is activated and the BD99010 and BD99011 is turned off.
(12) Thermal shutdown (TSD)
If the chip temperature (Tj) reaches or exceeds ca. 175°C (typ.) the output is turned off. Switching will resume
with soft start when the temperature drops below ca. 150 °C (typ.)
(13) Over voltage protection(OVP)
The BD9901x is equipped with an integrated over voltage protection (OVP) for output voltages exceeding 10%
above nominal output voltage. The OVP terminates switching until the output voltage drops below nominal value
again before resuming normal operation. The OVP is intended as a last-resort protection mechanism and should
never trigger in well-designed applications. Essentially there are two main root causes for an OVP event in a
practical application:
Extremely fast and extreme input voltage variations, for instance a supply voltage step from a few volts to a
maximum of 36V in a few micro seconds. Normally, an appropriate input filter should prevent this from
occurring.
Extreme load current variations from maximum current to zero in very short time, for instance caused by a
mechanical fuse or relay to trip.
Also it should be noted that when the output load is zero for a longer time while the ambient temperature is
extremely high (above 105ºC) a small leakage current through the high-side switch inside the BD9901x can
cause the output voltage to be higher than the OVP level. In case this might happen in the application under
extraordinary conditions, it is advised to bleed a small output current exceeding this leakage. Naturally, this
current increases the ultra-low quiescent current of 22 µA of a typical BD9901x application.
www.rohm.com
© 2013 ROHM Co., Ltd. All rights reserved.
TSZ22111・15・001
TSZ02201-0W1W0AL00030-1-2
07.Jul.2014 Rev.003
4/28
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