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TEA1738T

GreenChip SMPS control IC

NXP Semiconductors. 

NXP Semiconductors

TEA1738T; TEA1738LT

GreenChip SMPS control IC

7. Functional description

7.1 General control

The TEA1738(L) contains a flyback circuit controller, a typical configuration of which is

shown in Figure 3.

D1

R3

C1

R1

C2

R2

R4

Θ

O1

VINSENSE 5

4 ISENSE

PROTECT

CTRL

OPTIMER

6 TEA1738T 3 DRIVER

7 TEA1738LT 2 GND

8

1 VCC

C4 R8

C5

Fig 3. Typical configuration

T1

S1

R10

R6

C6

D3

C7

Z1

O1

R9

D2

001aan169

7.2 Start-up and UnderVoltage LockOut (UVLO)

Initially, the capacitor on the VCC pin is charged from the high voltage mains via resistor

R3.

If VCC is lower than Vstartup, the IC current consumption is low (10 μA typical). When VCC

reaches Vstartup the IC first waits for pin VINSENSE to reach the Vstart(VINSENSE) voltage

and for pin PROTECT to reach the Vdet(L)(PROTECT) voltage. When both levels are

reached, the IC charges the ISENSE pin to the Vstart(soft) level and starts switching. In a

typical application the supply voltage is taken over by the auxiliary winding of the

transformer.

If a protection is triggered the controller stops switching. Depending on the protection

triggered it either causes a restart or latches the converter to an off-state.

A restart caused by a protection rapidly charges the OPTIMER pin to 4.5 V (typical). The

TEA1738(L) enters Power-down mode until the OPTIMER pin discharges down to

1.2 V (typical). In Power-down mode, the IC consumes a very low supply current

(10 μA typical) and the VCC pin is clamped at 22 V (typical) by an internal clamp circuit.

When the voltage on pin OPTIMER drops below 1.2 V (typical) and the VCC pin voltage is

above the VCC start-up voltage (see Figure 4), the IC restarts.

When a latched protection is triggered, the TEA1738(L) immediately enters Power-down

mode. The VCC pin is clamped to a voltage just above the latch protection reset voltage

(Vrst(latch) + 1 V).

TEA1738T_TEA1738LT

Product data sheet

All information provided in this document is subject to legal disclaimers.

Rev. 2 — 14 January 2011

© NXP B.V. 2011. All rights reserved.

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