
TB7101F(T5L1.2,F)/(T5L1.5,F)/(T5L1.8,F)/(T5L2.5,F)/(T5L3.3,F)
2009-10-26
11
IN
OUT
L
osc
OUT
IN
V
I
f
V
L
Δ
=
V
5
V
3.3
mA
300
MHz
1
V
3.3
V
5.0
=
(2)
= 3.7 μH
Figure 2 Inductor Current Waveform
Output Capacitor Selection
Use a ceramic capacitor as the output filter capacitor. Since a ceramic capacitor is generally sensitive to
temperature, choose one with excellent temperature characteristics (such as the JIS B characteristic). As a rule
of thumb, its capacitance should be 10
μF or greater for TB7101F (T5L3.3, F), TB7101F (T5L2.5, F), TB7101F
(T5L1.8, F), and 20
μF or greater for TB7101F (T5L1.5, F), TB7101F (T5L1.2, F). 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.
Component Values (@VIN = 5 V, Ta = 25°C)
These values are presented only as a guide.
The following values may need tuning depending on the TB7101F’s input/output conditions and the board
layout.
Inductance
Input Capacitance
Output Capacitance
Product
L
CIN
COUT
TB7101F (T5L1.2, F)
3.3
μH
10
μF
22
μF
TB7101F (T5L1.5, F)
3.3
μH
10
μF
22
μF
TB7101F (T5L1.8, F)
3.3
μH
10
μF
10
μF
TB7101F (T5L2.5, F)
3.3
μH
10
μF
10
μF
TB7101F (T5L3.3, F)
3.3
μH
10
μF
10
μF
Undervoltage Lockout (UVLO)
The TB7101F has undervoltage lockout (UVLO) protection circuitry. The TB7101F does not provide output
voltage (VOUT) until the input voltage has reached VUVR (2.5 V typ.). UVLO has hysteresis of 0.1 V (typ.). After
the switch turns on, if VIN drops below VUV (2.4 V typ.), UVLO shuts off the switch at VOUT.
Figure 4 Undervoltage Lockout Operation
Soft start
VIN
Hysteresis:
ΔVUV
Undervoltage lockout
detection voltage: VUV
Switching operation stops
GND
VOUT
GND
Undervoltage lockout
recovery voltage: VUVR
Switching operation starts
Δ
I L
IL
osc
f
1
T
=
IN
OUT
ON
V
Τ
T
=
0