tb7107fn TOSHIBA Semiconductor CORPORATION, tb7107fn Datasheet - Page 7

• Manufacturer Part Number: tb7107fn
• Description: Buck Dc-dc Converter Ic
• Manufacturer: TOSHIBA Semiconductor CORPORATION

Output Filter Capacitor Selection
sensitive to temperature, choose one with excellent temperature characteristics. The large capacitance improves
load response characteristics. As a rule of thumb, its capacitance should be 10 μF or greater for applications.
The capacitance should be set to an optimal value that meets the system’s ripple voltage requirement and
transient load response characteristics. Since the ceramic capacitor has a very low ESR value, it helps reduce
the output ripple voltage; however, because the ceramic capacitor provides less phase margin, it should be
thoroughly evaluated.
Rectifier Selection
GND pins. It is recommended that either CMS02 or CRS15, be used as the Schottky barrier diode. If a large
voltage overshoot is on the L
of R
Schottky barrier diode tends to increase due to an increased reverse current caused by the rise in ambient
temperature and self-heating due to a supplied current. The rated current should therefore be derated to allow
for such conditions in selecting an appropriate diode.
Soft-Start Feature
soft-start time can be calculated as follows:
power-up and when the voltage at the EN pin has changed from logic low to logic high.
Overcurrent Protection（OCP）
Undervoltage Lockout (UVLO)
voltage (V
the switch turns on, if V
I
reduced and output current will be restricted further if output voltage falls and the voltage of V
below the overcurrent pulse skip detection voltage V
LIM
Use a low-ESR electrolytic or ceramic capacitor as the output filter capacitor. Since a capacitor is generally
A Schottky barrier diode should be externally connected to the TB7107FN as a rectifier between the L
The TB7107FN has a soft-start feature.
If the SS pin is left open, the soft-start time, t
The soft-start time can be extended by adding an external capacitor (C
The soft-start feature is activated when the TB7107FN exits the undervoltage lockout (UVLO) state after
The TB7107FN has undervoltage lockout (UVLO) protection circuitry. The TB7107FN does not provide output
The TB7107FN has built-in overcurrent protection with pulse skip. When the peak current of L
S
=3.5A(typ.), the ON time of the high-side switch(internal) will be limited. Switching frequency will be
= 4.7 Ω and a capacitor of C
t
SS2
OUT
=
. 0
16
) until the input voltage has reached V
⋅
C
V
SS
GND
GND
V
OUT
IN2
·························· (5)
IN
drops below V
X
Figure 4 Undervoltage Lockout Operation
pin, it reduces the voltage to connect a series CR network consisting of a resistor
S
= 470 pF with the Schottky barrier diode in parallel. Power loss of the
Switching operation
detection voltage V
Undervoltage lockout
UV
stops
(3.2 V typ.), UVLO shuts off the switch at V
t
C
SS
SS2
SS
, for V
: Capacitor value (μF)
: Soft-start time (in seconds) when an external capacitor is
LOC
UVR
connected between SS and GND.
7
OUT
(0.3V typ.) during overcurrent protection .
recovery voltage V
UV
Undervoltage lockout
(3.5 V typ.). UVLO has hysteresis of 0.3 V (typ.). After
defaults to 1 ms (typ.) internally.
Soft start
Switching operation starts
SS
UVR
Hysteresis: ΔV
) between the SS and GND pins. The
UV
OUT
.
FB
TB7107FN
X
2010-03-23
pin drops
pin exceeds
X
and