bd9842fv ROHM Co. Ltd., bd9842fv Datasheet - Page 9

• Manufacturer Part Number: bd9842fv
• Description: Dual-output High Voltage High-frequency Step-down Switching Regulator Controller Type
• Manufacturer: ROHM Co. Ltd.

7) STB (Standby/Master/Slave function)
Precaution here is as follows:
8) OUT 1/2 (Output: External FET gage drive)
9) Protection (other protection functions)
Standby mode, slave mode, and normal (master) mode can be switched by STB terminal (pin 15).
1. When STB<0.5V, standby mode is set.
2. When 2.4V<STB<2.6V, slave mode is set.
3. When STB>3.0V, normal operation mode is set.
When switching between standby mode and normal (master) mode, the current passes the area of slave mode.
When starting, if the time when 0.5V<STB<3.0V is long, the mode is switched with CT remaining unstable. Therefore
start within a time when UVLO is canceled (within 100 microseconds approx.) for activation time of STB.
When falling, once normal (master) mode is set, normal (master) mode is fixed until UVLO operates, and it does not
depend on falling speed of STB.
OUT terminal (pin 10 and 11) is capable of directly driving
the gate of external (PchMOS) FET. Amplitude of output is
restricted between Vcc and C5V (Vcc 5V), and is not
restricted by voltage resistance of gate by input voltage,
which allows broad selection of FET.
However, for precaution when selecting FET, there is a
restriction that input capacity of gate is determined by
current capability of C5V and permissible loss of IC,
therefore refer to the permissible range in the graph on the
right when determining FET.
This IC is equipped with low input malfunction prevention
circuit (UVLO) and abnormal temperature protection
circuit (TSD) in addition to overcurrent detection circuit
(OCP).
Low input malfunction prevention circuit is for preventing
unstable output when input voltage is low.
Three positions of Vcc (3.2V), VREF(2.35V), and C5V(Vcc-3V) are monitored, and output is made only when all are
canceled. (See the timing chart.)
Abnormal temperature protection circuit is for protecting IC chip from destruction for preventing runaway when abnormal
heating is caused on IC exceeding rated temperature. (It does not operate normally.)
Apply a design with full margin allowed for heating in consideration of permissible loss.
Output stops (OUT=H) and REG also stops. Circuit current is also Isc = 0 microA here.
Operation status is set, but OSC block alone is stopped, CT terminal is High-Z here, and triangular wave is not output.
(PWM circuit and protection circuit perform the same operation as usual.) Therefore, if the controller is used in this
mode without using master IC, triangular wave is not emitted, operation is unstable, and normal output cannot be
obtained. Be careful.
All circuits operate and triangular wave is output. Use the controller normally in this range.
9/15
1.E-07
1.E-08
1.E-09
1.E-10
100
Permissible range
Area below each line under each condition
Fig.35 OUT 端子外付け容量許容範囲
Switching f requency [kHz]
Fig.36
1000
Cout_max
Cout_max
(Vcc=10V)
Cout_max
(Vcc=20V)
Cout_max
(Vcc=30V)
10000