Datasheet
R4
43k
R3
59k
V1
Output of external
DC DC converter
V2
1.5V/3A
Vin
2.5V to 6V
PVIN
PVIN
EN FB
C1
10 Fm
L1
470nH
C2
22 Fm
R1
140k
SW
TPS62090
SW
Power Good
AVIN
R2
160k
SS
R3
500k
AGND
PG
VOS
FREQ
CP
CN
C3
10nF
1
2
3
4
5
6
PGND PGND
7
8
9
10
11
12
13
14 15
16
R3 R1
= x 1.56
R4 R2
1.25V
R4 =
300μA
TPS62090, TPS62091
TPS62092, TPS62093
www.ti.com
SLVSAW2A –MARCH 2012–REVISED MARCH 2012
Start-up Tracking (SS)
The softstart pin can also be used to implement output voltage tracking with other supply rails. The internal
reference voltage follows the voltage at the softstart pin with a fraction of 1.56 until the internal reference voltage
of 0.8 V is reached. The softstart pin can be used to implement output voltage tracking as shown in Figure 28.
Figure 28. Output Voltage Tracking
In Figure 28, the output V2 will track the voltage applied to V1. The voltage will track simultaneously when
following conditions are met:
(5)
As the fraction of R3/R4 becomes larger the voltage V1 will ramp up faster than V2 and if it gets smaller than the
ramp will be slower than V2. R4 needs to be determined first using Equation 6.
(6)
In the calculation of R4, 300 µA current is used to achieve sufficient accuracy by taking into account the typical
7.5 µA soft-start current. After determining R4, R3 can be calculated using Equation 5.
Short Circuit Protection (Hiccup-Mode)
The device is protected against hard short circuits to GND and over-current events. This is implemented by a two
level short circuit protection. During start-up and when the output is shorted to GND the switch current limit is
reduced to 1/3 of its typical current limit of 4.6 A. Once the output voltage exceeds typically 0.6 V the current limit
is released to its nominal value. The full current limit is implemented as a hiccup current limit. Once the internal
current limits is triggered 32 times the device stops switching and starts a new start-up sequence after a typical
delay time of 66 µS passed by. The device will go through these cycles until the high current condition is
released.
Output Discharge Function
To make sure the device starts up under defined conditions, the output gets discharged via the VOS pin with a
typical discharge resistor of 200 Ω whenever the device shuts down. This happens when the device is disabled
or if thermal shutdown, undervoltage lockout or short circuit hiccup-mode is triggered.
Power Good Output (PG)
The power good output is low when the output voltage is below its nominal value. The power good will become
high impedance once the output is within 5% of regulation. The PG pin is an open drain output and is specified to
typically sink up to 1 mA. This output requires a pull-up resistor to be monitored properly. The pull-up resistor
cannot be connected to any voltage higher than the input voltage of the device.
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