S-8341A30AFT-T2-G Seiko Instruments, S-8341A30AFT-T2-G Datasheet - Page 19

• Manufacturer Part Number: S-8341A30AFT-T2-G
• Description: IC REG SW 600KHZ 3.0V 8-TSSOP
• Manufacturer: Seiko Instruments
• Type: Step-Up (Boost)r

Specifications of S-8341A30AFT-T2-G

• Internal Switch(s): No
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 3V
• Frequency - Switching: 600kHz
• Voltage - Input: 0.9 ~ 6 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-TSSOP
• Power - Output: 300mW
• Output Voltage: 3 V
• Operating Temperature Range: - 40 C to + 85 C
• Mounting Style: SMD/SMT
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Output: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

STEP-UP, 600 kHz, PWM CONTROL OR PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER
Rev.4.0
4. Current Limit Circuit
Figure 12 IL
The current limit circuit of the S-8340/8341 Series protects the external transistors from being damaged by heat due
to an overload or magnetic saturation of coils. Inserting a SENSE resistor (R
source or external NPN bipolar transistor emitter and Vss and entering a connection point with a sensor resistor into
the SENSE pin enables the current limit to function. Refer to “ Standard Circuit”.
A current limiting comparator in the IC monitors the SENSE pin for reaching the current limit detection voltage
(V
oscillator so that the current flowing in the external transistor is limited. At the ON signal of the next clock, the
external transistor is turned on and the current limit detection function is resumed.
However, this current limit circuit contains a CR filter with a time constant (τ = 220 ns (typ.)) between the SENSE
pin and the current limiting comparator in the IC to prevent detection errors caused by the spike voltage generated
at the SENSE pin. If the time (pulse width t
until the current limit circuit operates is short, the current value that is actually limited becomes higher than the
current limit setting value determined by V
expressed by the following equation :
Remark
Caution Therefore, this current limit function does not guarantee full protection of external parts by I
For example, usage when the current value that the current limit circuit actually functions to raise the current limit
set value decided by V
the output voltage or situations when the output voltage falls due to the activation of the current limit circuit and
become close to the input voltage.
Figure 12 shows an example of the actually measured increase of the peak current flowing through the coil when
the current limit circuit functions while the input voltage is nearing the output voltage.
Figure 13 shows an example of the actually measured increase of the peak current flowing through the coil when
the output voltage drops and approaches the input voltage by increasing the output current after the current limit
circuit functions.
Input Voltage (V
If the current limit circuit is not used, remove R
the SENSE pin to V
SENSE
_00
I
LIMIT
3
2
1
0
4
= 120 mV (typ.)). Upon detection of the voltage, the external transistor is held off for one clock of the
1
PEAK
S-8340A50 (R
CR in the equation is determined by the internal CR filter and varies in the range 116 to 470 ns (220 ns
(typ.).)
V
devices.
SENSE
=
Measured at Activation of Current Limit
R
V
(V
SENSE
SENSE
IN
/R
OUT
2
) vs. Coil Peak Current (IL
SENSE
SS
Starts to Fall)
.
SENSE
SENSE
÷
⎛
⎜
⎝
under all operating conditions. Perform a thorough evaluation using the actual
V
1 e
= 51 mΩ)
IN
/R
3
−
(V)
SENSE
V
−
SENSE
ton 0.5
CR
×
that includes usage under the conditions that the input voltage become close to
/ R
4
SENSE
⎞
⎟
⎠
SENSE
Seiko Instruments Inc.
ON
PEAK
SENSE
5
: “H” level time at the EXT pin) after the external transistor turns on
/R
)
SENSE
and connect the external transistor source or the emitter and
as a side effect. The actual limit current value (I
Output Current (I
Figure 13 Measuring Coil Peak Current (IL
5
4
3
2
1
0
0
S-8340A50 (V
Current limit circuit
is activated
OUT
SENSE
) vs. Coil Peak Current (IL
1
IN
Influence of CR filter
= 3V, R
S-8340/8341 Series
) between the external FET
I
OUT
(A)
SENSE
V
SENSE
2
= 51 mΩ)
/ R
SENSE
PEAK
LIMIT
3
PEAK
LIMIT
)
) is
19
)
=