TS3300 Datasheet, PDF (10/12 Pages) Touchstone Semiconductor Inc – 0.6-4.5VIN, 1.8-5.25VOUT, 3.5-uA, Low Input Voltage, High-Efficiency Boost + LDO

TS3300
Boost Input Anti-Crush^TM Feature
The TS3300 includes an anti-crush^TM feature to
prevent the collapse of the input voltage to the boost
regulator when the input is a weak (high impedance)
source. If the input voltage drops below a determined
voltage threshold (settable by a resistor divider), the
boost regulator switching cycles are paused,
effectively limiting the minimum input voltage.
Anti-crush^TM is useful in applications where a buffer
capacitor at the boost’s output can service burst
loads, and the input source exhibits substantial
source impedance (such as with an old battery, or at
cold temperatures).
To set the anti-crush^TM voltage, a feedback pin
(BI FB) in conjunction with a voltage divider circuit
can be implemented as shown in Figure 4. The
feedback pin voltage is 392mV. It is recommended to
use large resistor values to minimize additional
current draw at the input.
Figure 4. Setting the Anti-Crush^TM Voltage with
a Voltage Divider
Using the following equation to solve for R5 for a
given R6 value, the output voltage can be set:
R3= ^{VANTI-CRUSHTM - 0.392 R4}
0.392
To set a 0.9V VANTI-CRUSHTM voltage with R4=1.37MΩ,
R3 is calculated to be 1.78MΩ. The anti-crush^TM
voltage is to be set above the minimum input voltage
specification of the TS3300.
Figure 5 shows a scope capture of the load step
response. The measurement was performed with the
anti-crush^TM voltage set to 0.9V. The output of the
Boost Regulator is pulsed with a 100mA load every
100ms for 1ms as shown by the pink curve, the input
voltage after a battery impedance of 10Ω drops from
1.2V to 0.9V as shown by the blue curve and the
boost output voltage drops by only 160mV as shown
by the yellow curve. The TS3300 quickly replenishes
the 500µF capacitor and the output of the boost
regulator returns to 3V.
Boost Load Step Response with V_Anti-CrushTM=0.9V
R_IN=10Ω, V_BI=1.2V, V_BO= 3V, C_BO=500µF, I_BO=100mA
Figure 5. Using Anti-Crush^TM Feature to Maintain Output
Regulation with Load Step Response
Figure 6 shows a scope capture of the anti-crush^TM
feature in action at start-up under a heavy capacitive
load of 500µF and an input source impedance of
10Ω. A high source impedance is typical of a weak
battery source. The measurement was performed
with the anti-crush^TM voltage set to 0.9V. The purple
and blue traces represent the input current and boost
output voltage respectively. At start-up, the current
rises up to 50mA and drops to approximately 30mA
for approximately 40ms in order to charge the output
capacitor. At this point, the voltage to the input of the
TS3300 is 0.9V until the boost output achieves
regulation.
Large Output Capacitor Start-up with V_Anti-CrushTM=0.9V
R_IN=10Ω, V_BI=1.2V, V_BO= 3V, C_BO=500µF
Figure 6. Using Anti-Crush^TM Feature at Start-up with Large
Output Capacitor and a 10Ω Input Impedance.
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TS3300 Rev. 1.0