TPS62420_15 Datasheet, PDF (11/38 Pages) Texas Instruments – TPS6242x 2.25-MHz 600-mA and 1000-mA Dual Step-Down Converter in Small 3-mm × 3-mm VSON Package

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TPS62420, TPS62421
SLVS676D – JUNE 2006 – REVISED JULY 2015
Feature Description (continued)
8.3.4 Enable
The device has for each converter a separate EN pin to start up each converter independently. If EN1 and EN2
are set to high, the corresponding converter starts up with soft-start.
Pulling EN1 and EN2 pin low forces the device into shutdown, with a shutdown quiescent current of typically 1.2
μA. In this mode, the P- and N-channel MOSFETs are turned-off and the entire internal control circuitry is
switched off. For proper operation the EN1 and EN2 pins must be terminated and must not be left floating.
8.3.5 DEF_1 Pin Function
The DEF_1 pin is dedicated to converter 1 and makes the output voltage selection very flexible to support
dynamic voltage management. Depending on the device version, this pin works either as:
1. Analog input for adjustable output voltage setting (TPS62420): Connecting an external resistor network to this
pin adjusts the default output voltage to any value starting from 0.6 V to V_IN.
2. Digital input for fixed default output voltage selection (TPS62421): In case this pin is tied to low level, the
output voltage is set according to the value in register REG_DEF_1_Low. The default voltage will be 1.2 V. If tied
to high level, the output voltage is set according to the value in register REG_DEF_1_High. The default value in
this case is 1.8 V. Depending on the level of pin DEF_1, it selects between the two registers REG_DEF_1_Low
and REG_DEF_1_High for output voltage setting. Each register content (and therefore output voltage) can be
changed individually through the EasyScale™ interface. This makes the device very flexible in terms of output
voltage setting; see Table 4.
8.3.6 180° Out-of-Phase Operation
In PWM mode the converters operate with a 180° turnon phase shift of the PMOS (high side) transistors. It
prevents the high-side switches of both converters to be turned on simultaneously, and therefore smooths the
input current. This feature reduces the surge current drawn from the supply.
8.3.7 Thermal Shutdown
As soon as the junction temperature, T_J, exceeds typically 150°C the device goes into thermal shutdown. In this
mode, the P- and N-channel MOSFETs are turned off. The device continues its operation when the junction
temperature falls below the thermal shutdown hysteresis again.
8.3.8 Short Circuit Protection
Both outputs are short circuit protected with maximum output current = I_LIMF (P-MOS and N-MOS). Once the
PMOS switch reaches its current limit, it will be turned off and the NMOS turned on. The PMOS only turns on
again, once the current in the NMOS decreases below the NMOS current limit.
8.4 Device Functional Modes
8.4.1 Soft-Start
The two converters have an internal soft-start circuit that limits the inrush current during start-up. During soft-
start, the output voltage ramp up is controlled as shown in Figure 7.
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