Datasheet

TPS62420-Q1
www.ti.com SLVSA56 –DECEMBER 2009
In case the operation mode will be changed from forced PWM mode (MODE/DATA = high) to Power Save Mode
Enable (MODE/DATA = 0) the Power Save Mode will be enabled after a delay time of typically t
timeout
, which is a
maximum of 520μs.
The forced PWM Mode operation is enabled immediately with Pin MODE/DATA set to 1.
ENABLE
The device has for each converter a separate EN pin to start up each converter independently. If EN1, EN2 are
set to high, the corresponding converter starts up with soft start as previously described.
Pulling EN1 and EN2 pin low forces the device into shutdown, with a shutdown quiescent current of typically
1.2μA. 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.
DEF_1 PIN FUNCTION
The DEF_1 pin is dedicated to converter 1 and works as an analog input for adjustable output voltage setting.
Connecting an external resistor network to this pin adjusts the default output voltage to any value starting from
0.6V to V
IN
.
180° OUT OF PHASE OPERATION
In PWM Mode the converters operate with a 180° turn-on 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.
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.
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.
EasyScale™: One Pin Serial Interface for Dynamic Output Voltage Adjustment
General
EasyScale is a simple but very flexible one pin interface to configure the output voltage of both DC/DC
converters. The interface is based on a master – slave structure, where the master is typically a μController or
Application processor. Figure 28 and Table 2 give an overview of the protocol. The protocol consists of a device
specific address byte and a data byte. The device specific address byte is fixed to 4E hex. The data byte
consists of five bit for information, two address bits and the RFA bit. RFA bit set to high indicates the Request
For Acknowledge condition. The Acknowledge condition is only applied if the protocol was received correctly.
The advantage of EasyScale compared to other one-pin interfaces is that its bit detection is, to a large extent,
independent from the bit transmission rate. It can automatically detect bit rates between 1.7kBit/sec and up to
160kBit/sec. Furthermore, the interface is shared with the Mode/Data Pin and requires therefore no additional
pin.
Protocol
All bits are transmitted MSB first and LSB last. Figure 29 shows the protocol without acknowledge request (bit
RFA = 0), Figure 30 with acknowledge (bit RFA = 1) request.
Prior to both bytes, device address byte and data byte, a start condition needs to be applied. For this, the
Mode/Data pin needs to be pulled high for at least t
Start
before the bit transmission starts with the falling edge. In
case the Mode/Data line was already at high level (forced PWM Mode selection) no start condition need be
applied prior the device address byte.
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